IL NUOVO SAGGIATORE Numero: BOLLETTINO DELLA SOCIETÀ ITALIANA DI FISICA G

Home , Arthur Ashkin, Franco Bassani, Orso Mario Corbino

Hanno collaborato a questo IL NUOVO SAGGIATORE numero: BOLLETTINO DELLA SOCIETÀ ITALIANA DI FISICA G. F. Bassani, G. Benedek, A. Bettini, M. Cardona, L. Cordone Nuova Serie Anno 24 • N. 5 settembre-ottobre 2008 • N. 6 novembre-dicembre 2008 G. Chiarotti, L. Cifarelli, R. Colella, A. Cresti, A. De Bortoli, Direttore Responsabile Vicedirettori Comitato scientifico E. Di Fabrizio, S. Focardi, Luisa Cifarelli Sergio Focardi G. Benedek, A. Bettini, P. Fortini, V. Grasso, G. Grosso, Giuseppe Grosso E. De Sanctis, E. Iarocci, G. La Rocca, G. Marchesini, I. Ortalli, R. Petronzio, W. Marx, I. Ortalli, E. Predazzi, P. Picchi, B. Preziosi D. Wiersma, A. Zichichi

sommario

3 In memoria di / In memory of Giuseppe Franco Bassani G. La Rocca, G. Grosso

5 EDITORIALE / EDITORIAL

SCIENZA IN PRIMO PIANO 7 Photons, dust, and honeybees D. Wiersma

77 The 40th anniversary of EPS: Gilberto Bernardini’s contributions to the Physics of the XX century A. Zichichi 98 Premio Nobel per la fisica 2008 A. Bettini 103 ESOF 2010 E. Predazzi, A. De Bortoli 105 Premio Sergio Fubini 2008 G. Marchesini 16 Electronic and transport properties 105 Progetto Lauree scientifiche: of pristine graphene nanoribbons borse SIF A. Cresti V. Grasso 106 In ricordo di: FISICA E... Frederick Seitz 27 Optical tweezers and their G. F. Bassani, G. Chiarotti applications Venzo De Sabbata E. Di Fabrizio P. Fortini Beatrice Palma-Vittorelli PERCORSI L. Cordone 39 Max Planck - A conservative revolutionary 108 opinioni M. Cardona, W. Marx 55 Fresnel, the prince of the opticians 109 RECENSIONI R. Colella 110 SCELTI PER VOI IL NOSTRO MONDO 62 Cerimonia Inaugurale 111 INDICE VOLUME 24 XCIV Congresso Nazionale della Società Italiana di Fisica Il Nuovo Saggiatore - Bollettino della Società Italiana di Fisica viene inviato gratuitamente ai Soci

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• Online by credit card through direct connection with the bank (BNL). This service can be accessed through the Members Area of the SIF website. We remind you that the Members Area is secured and can be accessed only through the username and password supplied to Members. • By cheque or credit card filling the payment form published on the web at the address: http://www.sif.it/SIF/en/portal/association . In case you wish to use the credit card also in this case, make sure to fill in the form in all its parts. • It is also possible to renew the association to the European Physical Society through the respective national societies. Members who wish to pay the EPS association fee through SIF can do so according to the instructions above. The EPS association fees are available on the SIF website at the above-indicated address. In memoria di Giuseppe Franco Bassani

La Società Italiana di Fisica per commemorare Giuseppe Franco Bassani, Presidente Onorario e Presidente nel periodo 1999-2007, curerà l’edizione di un volume in Suo onore e l’organizzazione di uno speciale evento celebrativo al prossimo Congresso Nazionale.

Franco Bassani, uno dei pionieri della moderna teoria dei è stato Direttore della Scuola Normale Superiore di Pisa dal solidi, è scomparso a Pisa il 25 settembre 2008, dopo una 1995 al 1999. è stato Presidente della Società Italiana di Fisica lunga malattia. dal 1999 al 2007. Nato a Milano nel 1929, studiò fisica all’Università di Pavia, I suoi maggiori risultati riguardano la teoria della struttura dove si laureò nel 1952, diventando poi ricercatore associato elettronica a bande dei semiconduttori, la fotofisica dei al gruppo dei Professori P. Caldirola e F. Fumi a Milano. centri di colore nei cristalli ionici, le proprietà ottiche Dal 1954 al 1956 lavorò accanto al Professor Seitz lineari e non lineari dei semiconduttori e dei materiali all’Università dell’Illinois, al suo ritorno in Italia ebbe il isolanti, la teoria degli eccitoni e polaritoni in sistemi di ruolo di assistente (Palermo: 1956-57, Pavia: 1957-59) e semiconduttori a bassa dimensionalità, comprese le strutture successivamente, dal 1959 al 1964, fu di nuovo negli Stati ibride organiche-inorganiche. Ha sviluppato un approccio Uniti come “associate physicist” presso l’Argonne National moderno al calcolo della risposta ottica di un cristallo basato Laboratory. Dal 1964 ha ricoperto il ruolo di professore di sull’introduzione dello pseudopotenziale per la struttura fisica teorica e di fisica dello stato solido in diverse Università elettronica a bande e sull’analisi della simmetria nel punto italiane (Messina: 1964-66, Pisa: 1966-69, critico. Il suo libro “Electronic States Roma: 1969-80) e dal 1980 al 2004 alla and Optical Transitions in Solids” (1975) Scuola Normale Superiore di Pisa. è scritto in collaborazione con G. Pastori stato “invited professor” presso l’Ecole Parravicini è considerato il testo di Polytechnique Fédérale di Losanna e riferimento classico per quel settore. l’Università dell’Illinois. Dal 2005 era Il suo primato internazionale non si professore emerito alla Scuola Normale limitava al solo settore teorico, poiché Superiore. egli si dedicava a tutti gli aspetti della Franco Bassani era “fellow” dell’ Institute ricerca scientifica; per esempio, fu lui la of Physics, dell’American Physical Society forza trainante che portò alla costruzione e dell’European Physical Society. Dal in Italia di macchine di radiazione di 1990 era membro dell’Accademia sincrotrone. Nazionale dei Lincei. Nel corso della sua lunga carriera, Franco Gli sono state conferite lauree honoris Bassani ha formato numerosi studenti causa dall’Università di Toulouse, che si sono fatti strada presso diverse dall’Ecole Polytechnique Fédérale di Istituzioni in Italia e all’estero ma che nel Losanna e dalla Purdue University. tempo hanno continuato a considerarlo Tra le tante onorificenze che ricevette guida e fonte di ispirazione. Ai suoi allievi ricordiamo Il Premio Somaini per la Fisica, il Premio Italgas per e ai suoi colleghi in tutto il mondo mancherà profondamente le Scienze dei Materiali e la Medaglia d’Oro di Benemerito della la sua presenza ma resterà sempre vivo in loro il suo ricordo Scienza e della Cultura del Presidente della Repubblica Italiana. di maestro, scienziato e amico. Franco Bassani è stato membro nell’Editorial Board di diverse riviste internazionali, in particolare di “Solid State Giuseppe La Rocca Communications” dal 1972 al 1986 e di “Europhysics Letters” Scuola Normale Superiore, Pisa dal 1986 al 1992. è stato presidente della Divisione Materia Giuseppe Grosso Condensata dell’European Physical Society dal 1986 al 1992. Università di Pisa In memory of Giuseppe Franco Bassani

To honor the memory of Giuseppe Franco Bassani, Honorary President and President in the years 1999-2007, the Italian Physical Society will publish a dedicated volume and organize a special celebration event on the occasion of the next National Congress.

Franco Bassani, one of the pioneers of the modern theory of 1992. He was Director of Scuola Normale Superiore from 1995 solids, died on 25 September 2008 in Pisa, after a long illness. to 1999. He was President of the Italian Physical Society from Born in 1929, he studied physics at the University of Pavia, 1999 to 2007. graduated in 1952, and became research associate in Milan His seminal scientific achievements concern the theory in the group of prof. P. Caldirola and prof. F. Fumi. From 1954 of the electronic band structure of semiconductors, the to 1956 he worked with prof. Seitz at the University of Illinois, photophysics of colour centers in ionic crystals, the linear then he was assistant professor in Italy (Palermo: 1956-57, and nonlinear optical properties of semiconductors and Pavia: 1957-59) and from 1959 to 1964 associate physicist insulators, the theory of excitons and polaritons in low at the Argonne National Laboratory. Since 1964 he was dimensional semiconductor systems, including hybrid professor of theoretical physics and of solid state physics in organic-inorganic structures. He has developed the modern several Universities in Italy (Messina: 1964-66, Pisa: 1966-1969, approach to the calculation of the optical response of a Rome: 1969-1980) and from 1980 to 2004 at Scuola Normale crystal based on the pseudopotential electronic band Superiore in Pisa. He had been on leave as invited professor structure and the critical point symmetry analysis. His book at the Ecole Polytechnique Fédérale in Lausanne (1972-73) “Electronic States and Optical Transitions in Solids” (1975) and at the University of Illinois (1979-80). Since 2005, he was coauthored with Giuseppe Pastori Parravicini has become the professor emeritus at Scuola Normale Superiore. classical reference in the field. His international leadership Franco Bassani had been a fellow of the Institute of Physics, of was not confined only to theory, as he devoted his attention the American Physical Society and of the European Physical to all aspects and implications of the scientific endeavour; for Society. He had been a national member of the Accademia instance, he has been the driving force in the establishment dei Lincei since 1990. He received honorary degrees from the of synchrotron radiation facilities in Italy. University of Toulouse, from the Ecole Polytechnique Fédérale During his long career, Franco Bassani tutored a very large in Lausanne and from Purdue University. Among many other number of pupils who have moved to many different honors, he received the Somaini Prize for Physics, the Italgas Institutions in Italy and abroad and have looked upon him for Prize in Material Sciences and the Gold Medal of the President inspiration and guidance over the years. He is deeply missed of the Republic of Italy for achievements in science and by former students and colleagues all over the world who will culture. always remember the teacher, the scientist and the friend. Franco Bassani served on the editorial board of many journals, and in particular was editor of Solid State Communications Giuseppe La Rocca from 1972 to 1986 and editor of Europhysics Letters from Scuola Normale Superiore, Pisa, Italy 1986 to 1990. He was Chairman of the Condensed Matter Giuseppe Grosso Division Board of the European Physical Society from 1986 to University of Pisa, Italy

Canneto Pavese editoriale / editorial

Giunge a termine il mio primo anno di proceedings dei corsi della Scuola Internazionale di Chimici, già dotata di un Ordine Professionale mandato alla guida della Società Italiana di Fisica “Enrico Fermi” di Varenna. ben consolidato che verrebbe ridenominato Fisica. Permettetemi di riassumere brevemente le A partire dal 2009 particolare attenzione sarà e suddiviso in più sezioni permettendo così azioni intraprese. rivolta al reclutamento in qualità di “Soci Invitati” un ingresso paritetico dei Fisici. Sono in fase È stato pubblicato all’inizio del 2008 e presentato dei giovani neolaureati (triennali) in Fisica. A loro di definizione, insieme alla Società Chimica con successo il rapporto SIF sull’energia in Italia, sarà concessa l’associazione gratuita alla SIF per Italiana (SCI) e al Consiglio Nazionale dei Chimici dapprima in un workshop internazionale a 2 anni allo scopo di promuovere e far conoscere (CNC), i passi formali della procedura. Con ogni Varenna (in aprile) e poi al Congresso Nazionale di le nostre attività. L’iniziativa mira a renderli probabilità, l’impresa si concluderà felicemente Genova (in settembre). Il rapporto è stato inviato maggiormente partecipi e consapevoli del nel 2009. ai rappresentanti delle istituzioni, degli organi proprio ruolo scientifico e professionale, e magari Anche quest’anno è stata dovutamente espletata di stampa, delle università, degli enti di ricerca e anche ad accendere in loro un briciolo di spirito dalla SIF la selezione dei migliori studenti delle imprese. Tradotto in Inglese, è stato anche di appartenenza a un’eletta Società come la SIF. per il “Progetto Lauree Scientifiche”. È anche distribuito nell’ambito della European Physical Nel 2009 sarà inoltre leggermente ridotta la quota risultata ancora una volta interessante e proficua Society (EPS) e delle maggiori Società europee. associativa dei giovani Soci con età inferiore ai 30 l’interazione della SIF con il Consiglio Universitaro Nel 2009 ulteriori studi in materia di energia anni. Nazionale (CUN) nel corso di un incontro allargato verranno intrapresi insieme alla Società Chimica È in corso un serio rentativo di rilancio delle (a Bologna, all’inizio di dicembre), volto a favorire Italiana (SCI). pubblicazioni propriamente SIF: Il Nuovo Cimento lo scambio di opinioni e la discussione all’interno È stata compiuto un importante sforzo di B/C, La Rivista del Nuovo Cimento e il Giornale di della comunità dei Fisici su questioni universitarie outreach, con il miglioramento e l’arricchimento Fisica (con i suoi Quaderni di Storia della Fisica). e di ricerca, alla luce delle nuove norme in vigore. del sito web della SIF, con un colorato (e Calorosamente rinnovo l’invito a pubblicare Altre iniziative, come la crezione di un gruppo apprezzato) rinnovamento della veste editoriale articoli su questi giornali i cui contenuti e di lavoro SIF per la scuola e l’università, sono in de Il Nuovo Saggiatore la cui distribuzione è stata obiettivi sono stati recentemente ridefiniti e il cui programma per il 2009. inoltre notevolmente allargata: adesso il bollettino impact factor, sia pure di poco, sta cominciando Infine è inevitabile il triste bilancio dei Soci che è inviato a migliaia di destinatari, cultori della a risalire. Da segnalare invece, anche grazie a sono venuti a mancare nel corso di quest’anno. materia e non solo. È stato finalmente completato voi, il crescente successo delle pubblicazioni a Molti di loro saranno ricordati su queste pagine. il database elettronico dei Soci SIF tramite il quale partenariato europeo cui la SIF contribuisce in Primo fra tutti, il nostro Presidente Onorario sono state attivate nuove procedure telematiche maniera sempre più efficace e significativa: EPJ Giuseppe Franco Bassani cui questo numero de Il di associazione, di iscrizione al Congresso e di (The European Physical Journal) e, in particolare, Nuovo Saggiatore è dedicato. accesso privilegiato online alla cosiddetta “Area EPL (EuroPhysics Letters). Grazie a tutti voi per il supporto e la Soci”. Nell’Area Soci è già possibile consultare Il traguardo di un Ordine Professionale per i Fisici collaborazione. I miei migliori auguri per un felice gratuitamente l’intero archivio storico de Il sembra ormai vicino grazie all’iniziativa della 2009, Nuovo Cimento. Nel 2009 il servizio sarà esteso ai SIF e alla reazione positiva della comunità dei Luisa Cifarelli

My first year of mandate as President of the Italian International School of Physics of Varenna. would be renamed and split into sections, in order Physical Society (Società Italiana di Fisica, SIF) is Starting from 2009 special attention will be to admit also physicists on equal terms. The formal now coming to an end. Let me briefly summarize devoted to enlisting the junior graduates in actions to achieve this merging are being defined the undertaken initiatives. Physics (with three-years course degree) as by the Chemists National Council (Consiglio At the beginning of 2008 the SIF report on energy “Invited Members”. They will be granted a free Nazionale dei Chimici, CNC), together with the in Italy has been published and successfully membership for the first 2 years with the aim to Italian Chemical Society (SCI). In all likeliness the presented, first at an international workshop promote our Society and make them know our whole operation could be successfully finalized by in Varenna (April) and then at the SIF National activities. With this intiative we wish to make them the end of 2009. Congress in Genoa (September). The report has more concerned and more self-conscious of their This year too SIF has contributed to the “Progetto been sent to representatives of institutions, specific scientific role, and hopefully to little revive Lauree Scientifiche” (to promote hard-sciences press media, university, research organizations their sense of belonging to a learned Society such degrees) by selecting the best students. Also and industry. In its English version it has also as SIF. Moreover in 2009 membership dues for the relationship between SIF and the National been distributed within the European Physical members under 30 years of age will be slightly University Council (Consiglio Universitario Society (EPS) and the major physical Societies in reduced. Nazionale, CUN) has newly shown to be fruitful in Europe. In 2009 we foresee to further investigate A serious attempt to relaunch our own the occasion of an enlarged meeting (in Bologna, energy problems in collaboration with the Italian publications, namely Il Nuovo Cimento B/C, beginning of December) to exchange opinions Chemical Society (Società Chimica Italiana, SCI). La Rivista del Nuovo Cimento, Giornale di Fisica and discuss within the physicists community, A remarkable effort has been made for outreach (with its Quaderni di Storia della Fisica), is being about university- and research-related matters purposes. The SIF web site has been upgraded undertaken. I warmly invite you to consider with reference to the new rules in force. Other and enriched with new information and facilities, publishing papers in these journals, whose aims initiatives are foreseen for 2009, such as the our bullettin Il Nuovo Saggatore changed to a and scopes have been recently redefined, and creation of a SIF working group dedicated to newer (much appreciated) all in colours graphic whose impact factor has shown an improvement, school and university problems. presentation and, more important, it is now although to a tiny degree. Worthy of note is the And last, unavoidable and sad is the balance of distributed to a wider audience of thousands increasingly successful performance, also thanks all members that passed away in the course of readers also outside the physicists community. to you all, of the journals published in cooperation the year. Many of them will be remembered on The electronic database of SIF Members has with European partners to which SIF contributes this journal pages. First among all, our Honorary been finally completed, thus allowing new online more and more effectively and proficuously: EPJ President Giuseppe Franco Bassani whom this procedures for membership renewal, registration (European Physical Journal) and, in particular, EPL issue of Il Nuovo Saggiatore is dedicated to. at the Congress, and priviledged access to the (EuroPhysics Letters). Thanks to you all for the continuous support and so-called “Members Area”. Through this area the The goal of a Professional Roll for Physicists has collaboration. With my best wishes for a joyful free consultation of the complete electronic now good chances to be reached thanks to the SIF 2009, archive of Il Nuovo Cimento is already enabled. In initiative that has been welcomed by the Chemists Luisa Cifarelli 2009 we expect to extend this service also to the community. This community is already endowed proceedings of the courses of the “Enrico Fermi” with a well-established Professional Roll which

vol24 / no5-6 / anno2008 > scienza in primo piano

Photons, dust, and honeybees

Diederik Wiersma* European Laboratory for Non-linear Spectroscopy (LENS), Florence and INFM-CNR BEC, Trento, Italy

People working with optics and lasers usually try to avoid dust on their equipment as much as possible. Dust particles scatter light randomly in all directions and this is often detrimental to the performance of optical devices and lasers. In this articles we will see that it is possible to turn this situation upside down and actually make use of multiple light scattering to study interesting physical phenomena. In particular, we will discuss optical Lévy flights and super diffusion, and various interference effects like weak and strong localization of light waves.

A Lévy flight is an often used term to indicate random walk 1 Beyond Gaussian disorder processes. Imagine you are walking in downtown Manhattan In our understanding of transport processes we usually and at every street crossing you randomly decide if you go assume that the distance covered at every step of the random left or right (or forward or backwards). The trajectory that you walker is not varying very much. This simplification seems follow this way is called a random walk and the distance that reasonable at first sight, since it allows to consider only the you cover between crossings is its step length. Random walks average value of this step length, the so-called mean free lie at the basis of many statistical processes in economics, path. Physicists use this simplification, which is based on the biology, and physics. Einstein already applied this concept central-limit theorem, very often, sometimes even without to describe the transport of a small particle in a fluid, called being aware of it. Brownian motion. Many transport processes, ranging from In a Lévy flight the step length of the random walk is far from electrical conduction, to heat and sound diffusion, are based constant and this means that in some occasions very large upon random walks. steps can occur [2-4]. These large steps not only mean that Light diffusion has been a power tool to study random walk the random walker can cover a much vaster area, but they processes, thanks to the analogies that exist between light also lead to the counter-intuitive property that the average diffusion and diffusion of particles in other fields of research, step length diverges. Or in other words, the central-limit like solid-state physics, acoustics, and atomic physics [1]. theorem cannot be applied anymore and it is not possible to Light has the advantage that it allows for high-precision define an average step length of a Lévy flight. experiments with relatively simple tools. From such optical While this sounds exotic at first sight, it turns out that many experiments it is possible to learn important concepts that processes in nature are actually based on Lévy flights. An then can be applied to other fields in physics as well. important example is that of the search pattern that animals follow in search for food. Honeybees that are placed in a new environment will perform a Lévy flight to scan the area [5]. By * e-mail: [email protected] performing a Lévy flight they can cover a much vaster region URL: www.lens.unifi.it/cs/ or www.complexphotonics.org then by performing a normal random walk. At the same

vol24 / no5-6 / anno2008 > scienza in primo piano time they manage to gather detailed local 1 information in their search. Other examples of Lévy processes are the trend of the stock market, the distribution of human travels, and the diffusion of liquids in the Earth’s crust. The latter is, of course, extremely relevant for the understanding of how pollution spreads from a local source. Based on a regular-diffusion process it can take millions of years before a certain contaminant reaches a drinking water area, while with a Lévy flight this can take only months.

2 Light transport Given the vast amount of literature on optical random walks and light diffusion, one might wonder if it is possible to find or realize an optical material in which light waves perform a Lévy flight. In such aLévy glass the photons would perform a random walk with a step length distribution given by Lévy statistics. The result would be an optical super diffuser. The idea is visualized in fig. .1 To realize an optical Lévy flight, one might be inclined to develop scattering materials with self-similar (fractal) structure. This approach turns out not to work, in practice, due to the dependence of the scattering cross-section on size. In, for instance, a fractal-shaped colloidal suspension, the larger particles would be subject to resonant (Mie) scattering, while the smaller particles would hardly scatter at all (Rayleigh limit). The solution is to find a way to modifiy the density of scatterers, instead of their size. This way one can locally obtain a scattering mean free path that strongly Fig. 1 Visualization of the concept of a Lévy flight of light. The step depends on the position inside the sample [6]. length distribution of the random A relatively easy, but so far unexplored walk is heavy-tailed, meaning possibility to do this, is by using high refractive that a small number of large steps index scattering particles (titanium dioxide in dominate the transport process. (Photo by Leonardo and Diederik our case) in a glass matrix. The local density of Wiersma.) scattering particles is modified by including glass microspheres of a well-chosen (and highly non-trivial) size distribution. These glass microspheres do not scatter since they are incorporated in a glass host with the same refractive index. Their sole purpose is to modify locally the density of scattering elements. This concept is illustrated in fig. .2 The random walk in regular diffusive materials has a Gaussian step length distribution with

< il nuovo saggiatore D. wiersma: photons, dust, and honeybees

average step length given by the mean free 2 path l:

(1) , with s the scattering cross-section and N the density of scattering elements. The angular brackets indicate an average over the sample volume. To obtain a Lévy flight, the material should give rise to a step length distribution with a heavy tail, decaying as

(2) , with P (z) the probability of a step of length z and a a parameter that determines the type of Lévy flight. Such a step length distribution leads to superdiffusion: the average squared displacement 〈x 2〉 increases faster than linearly with time,

(3) , where g is a parameter that characterizes the superdiffusion andD a generalized diffusion constant. For g > 1 we have superdiffusion while for g = 1 we recover regular diffusive behavior. Normal diffusion is therefore a limiting case of a Lévy flight. The parameter a can be shown to be related to the superdiffusion exponentg as: g = 3 - a for this method it is possible to obtain a Lévy 1 ≤ a < 2. The moments of this distribution flight with any value ofa . For simplicity it is Fig. 2 Comparison of a regular diverge for a < 2, which means that the convenient to consider the case a =1, since it random walk with Gaussian disorder (top panel) to a Lévy average in eq. (1) cannot be taken anymore is one of the few Lévy distributions that has flight in which the step length over the entire sample. One can still interpret a simple analytical expression, namely the distribution has heavy (power law) Ns, however, as the local scattering strength of Cauchy distribution. tails (bottom panel). the material. Our samples were made, in practice, by suspending titanium dioxide (TiO2) 3 Ohm’s law of conductance nanoparticles in sodium silicate, together A simple but effective way to analyze a with a precisely chosen distribution Ps (d) of diffusion process is by considering Ohm’s law glass microspheres of different diameterd . of conductance. Ohm’s law for electrons in a

The total concentration of TiO2 nanoparticles resistor tells us that the total resistance of a was chosen such that, on average, about series of components equals the sum of the one scattering event takes place in the, resistance of each individual component. This

TiO2-filled, space between adjecent glass linear sum rule exists also for diffuse light. microspheres. The step length distribution Consider a vertical slab of disordered optical is then determined by the density variations material on which light is incident from the induced by the distribution Ps (d) of the glass left. This light will be diffusely scattered inside microspheres. To obtain a Lévy flight with this material and the total amount of (diffuse) coefficienta , one can derive that a diameter light that comes through the material on the 2+a distribution Ps (d) = 1/d is required. With right side is the total transmission. This total

vol24 / no5-6 / anno2008 > scienza in primo piano é 3 4 a) é a)

1 T = 1 + AL α/2

b) é b) é

Fig. 3 Total transmission (angular integrated) versus thickness through a block of Lévy glass (points). In a regular diffusion process the transmission decays linear with thickness (blue solid line), whereas in a Lévy process the decay of the transmission with thickness is much slower (red solid line).

Fig. 4 Spatial distribution of the intensity on the output surface (backside) of a transmission depends linearly on the is superdiffusive. Thea coefficient in block of Lévy glass which is excited on the front surface with a point source. thickness of the slab, so that the optical this case is a = 0.948 ± 0.09, which is The average transmission on the output “resistance” of the material depends very close to the design value of 1.0 of surface is plotted versus radial distance linearly on its thickness. The reason the Cauchy-type Lévy flight. from the center. The spatial profile in the for this analogy between photons Lévy case shows a characteristic sharp cusp and slowly decaying wings, whereas and electrons is that in both cases the a diffusive sample presents a profile close physics can be described by a diffusion 4 Superdiffusion to a Gaussian lineshape. equation. The power law step size distribution a) Experimental data. b) Result of Monte Carlo simulations. The difference in For superdiffusion, Ohm’s law can be of a Lévy flight is expected to give rise absolute widths between experiment and generalised in the following form: to strong fluctuations in the transport simulation can be explained by internal properties of individual samples. In the reflections at the boundary of the sample, (4) , total transmission profile one should which were not taken in account in the simulations. therefore observe large differences where L is the thickness. For the from one disorder realization to Fig. 5 Spatial intensity distribution of diffusive casea = 2, we recover Ohm’s another. In comparison, a common the light that is multiply scattered by a law of conductance. diffusive sample would show nearly random system. The strongly fluctuating In fig. 3 the experimentally recorded no fluctuations. If one compares the intensity is due to interference and is characteristic for speckle patterns. Note transmission through Lévy glass is transmission of a Lévy glass with that of that in between the spikes the intensity compared with theory. We can see that a regular diffusive system of the same become really zero. they decay much slower than linearly, thickness, one can indeed observe showing that transport in these samples huge differences while the result for the

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diffusive sytem is nearly constant. influence of internal reflections at the interference effects can, in principle, The characteristics of the Lévy flight interface at the sample, which were not survive. If we shine a laser beam on also survive if we perform an average taken into account in the Monte Carlo a white material like a piece of paper over a large number of observations. simulations. we see a grainy pattern of intensity The resulting profiles of the transmitted The most important feature of these maxima and minima. This is due to intensity on the output surface are curves lies in their slowly decaying interference between waves that have plotted in fig. 4and compared with wings. This means that the Lévy been scattered randomly inside the the results of Monte Carlo simulations. flight spreads the light much more paper and is called laser speckle [7]. Both experimental and simulation efficiently than the regular Gaussian (See fig. .)5 Speckle is present also inside results show the same features. For the system. This is a direct consequence a random system in the form of local diffusive system we observe that the of the superdiffusive transport in Lévy maxima and minima. Speckle occurs in profile has, as expected, a bell-shape systems. any disordered material, no matter what profile, which is very close to a Gaussian its specific microscopic structure or curve. For the Lévy sample, on the other level of disorder. hand, the profile presents a well-marked 5 Interference effects cusp and has tails that decay much An important property of light waves more slowly than in the diffusive case. that we have not considered so far, 6 Weak localization The agreement between experimental is the fact that they can interfere. Another interference effect that is not and simulated profiles is very good. The The scattering that occurs in random well known, yet relatively simple and small discrepancy in the overall width materials and Lévy glasses is very fundamental, is that of coherent of the profile can be explained by the completely elastic, which means that backscattering, or weak localization [8].

vol24 / no5-6 / anno2008 > 11 scienza in primo piano 6 Consider a broad laser beam that is impingent on any random optical material, be it a white- painted wall, a block of marble stone, or a cup of sugar. The light rays will penetrate such material and perform their random walk. Most light will in the end come out of this random material again in the form of diffuse light. The effect of coherent backscattering occurs in the light that is backscattered from such a structure. Any random walk path can be followed either in the clockwise direction or counterclockwise. The crucial element that allows interference effects to occur is that the scattering along such a path is completely elastic. That means that the phase of the light waves will be complicated but precisely defined. It also means that the system is reciprocal: one follows the same path in either the clockwise or counterclockwise direction, the total accumulated phase will be the same. The outcoming rays that have followed the same path in opposite directions can therefore interfere with each other, and this interference 7 will be constructive in the exact backscattering direction. The result after summing over all paths is a cone of coherent backscattering which has a top that is twice as high as the intensity expected without interference. (See fig. .)6 Coherent backscattering is therefore a large effect. Moreover it occurs on any diffusively scattering material, so anything around us that looks white exhibits coherent backscattering. The full width at half maximum of such a coherent backscattering cone is a measure for the scattering strength of a random structure. In particular it depends linearly on the inverse of the mean free path times the wavelength of the light. This means that by measuring a coherent backscattering cone from a block of material it is possible to obtain a measure for the amount of structural disorder (see fig. ,7 Fig. 6 Reciprocal light paths Fig. 7 Examples of coherent where the coherent backscattering is reported in random systems lead to backscattering cones as observed from two materials of different scattering interference patterns in the from strongly scattering backscattered light. The materials. The broadest cone strength). This technique can be applied (and

sum of these interference has been recorded from TiO2 has been tested successfully) for determination patterns gives rise to a cone powders which are very close to of the level of caries in teeth. of enhance backscattering. Anderson localization. The onset This phenomenon also called of localization is manifest in the coherent backscattering or weak backscattering cone as a small localization is extremely robust reduction of the enhancement 7 Strong localization and occurs from any diffusive factor to values below 2.0. In fig. 7, one can also observe that the material. enhancement of the signal is close to two, due

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to interference. For the very strongly scattering material this enhancement drops slightly. 8 Although the effect is small, the reason behind this drop is quite fundamental. In very strongly scattering materials interference effects can lead to a strong version of localization, also called Anderson localization [9], being the optical counterpart of localization of electrons in strongly disordered conductors [10]. Anderson localization inhibits the free propagation of waves and the optical diffusion process thereby comes practically to a halt [11]. Although the detailed mechanism behind localization is quite complex, one can visualize the effect as being due to the formation of randomly shaped but closed modes with an overall exponentially decaying amplitude. (See fig. .)8 The average spatial extend of these localized modes defines a length scale called the localization length. The connection between weak and strong localization is then also immediately clear. While in the case of weak localization the interference occurs outside the sample between light waves that have travelled along half-closed loops, in strong localization the same interference occurs inside the sample along closed-loop paths. Localization is expected to occur when the disorder is so strong that the mean free especially photonic crystals, intrinsically suffer path l becomes smaller than the reciprocal from structural order. It is simply impossible wave vector, so that: k l ≤ 1. The product to make a perfect photonic crystal without k l is therefore often used as parameter to some level of randomness. This made it ever so characterize the amount of optical disorder, important to understand how disorder affects with the disorder increasing for decreasing the propagation of light and what the physics k l. Most optical materials in daily life have k l is behind disorder-related optical phenomena. values that are much bigger than one and are It also became clear, however, that disorder therefore only weakly to modestly scattering. is not necessarily a disadvantage. It was Even for very dense clouds we have k l values found, for instance, that disorder in photonic that are bigger than 106, so that light is crystals can lead to a very efficient trapping diffusively transported instead of trapped. This mechanism for optical waves [12]. This is very is also the reason why sunlight can penetrate promising for optical memory applications clouds diffusively. If clouds were to Anderson- and slow light devices and the disorder can be localize light, the incident sunlight would actually used as an advantage. be mostly reflected back, leaving the Earth Another fascinating application of diffusive completely dark on a cloudy day. materials is that of random lasing [13]. The multiple-scattering process is capable of Fig. 8 Typical intensity distribution trapping light very efficiently and, combined of Anderson-localized modes. The 8 Applications with an appropriate gain medium, this can be envelope of the modes decays The research on light diffusion and disordered used to create a laser source. Such a random exponentially and the limited spatial overlap between the photonic structures in general has seen an laser uses multiple scattering as confinement modes leads to a halt of transport. enormous boost in recent years. One of the mechanism and requires no mirrors or other The sharper features within the reasons is that most photonic materials, and form of cavity. (See fig. .)9 The output of such modes are due to residual speckle.

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a disordered amplifying material is, be, it had not been observed so far in understand each other. To understand of course, spread out over a broad any material, neither for sound wave better how light behaves in disordered angular range, but has otherwise propagation, nor for light, electrons, or optical materials, concepts come in several properties that are similar to heat transport. Studying food search from mathematics, statistical and the emission from a regular laser. Apart patterns of birds is of course fascinating, solid-state physics. To understand Lévy from having a narrow spectrum, the but not that easy to do on a large scale. glasses even means having optical output of a random laser can have a You cannot possibly follow the same engineers discussing with biologists surprisingly high level of coherence, amount of birds as you can collect and geophysicists. in the sense that the photon statistics photons in an optical experiment. This is, however, also the beauty of doing have the typical characteristics of the In addition, this material has a very new scientific research and is the key to coherent state as produced by a laser optical appearance which could make making significant progress in the future. [14]. A typical random laser spectrum is it interesting for jewelry or art objects. plotted in fig. 10. There exists a common Another property which can make it acnowledgements misconception that a laser requires interesting for applications is its very The results discussed in this paper a cavity to produce such coherent efficient diffusive power. This can help and many more on light in photonic emission. The key mechanism that leads the distribution of environmental light crystals and random systems have been to coherent emission is gain saturation, in lighting applications. It would also be obtained by the members of the micro which suppresses intensity fluctuations. interesting to try to implement optical and nano photonics group at the LENS Such gain saturation can be easily gain in these Lévy glasses to obtain a laboratory in Florence, being Pierre obtained also in random laser sources random laser based on superdiffusion. Barthelemy, Jacopo Bertolotti, Costanza when operating far enough above Toninelli, Silvia Vignolini, Francesca threshold. Intonti, Francesco Riboli, and the former Coming back to Lévy glass, one would 9 Future challenges members Stefano Gottardo, Riccardo like to use this material first of all to The interdisciplinary character of this Sapienza, Sushil Mujumdar, Matteo study the physics of Lévy transport research makes it both fascinating Burresi, and Paola Costantino. Pierre processes in an easy and controlled from one side but it also leads to the Barthelemy and Jacopo Bertolotti in way in the laboratory. No matter how enormous challenge to make research particular have realized the Lévy glass general this phenomenon seems to from very different communities experiments.

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10 Fig. 9 Concept of a random laser. Fig. 10 Typical shot-to-shot In a regular laser system light is spectral emission from a random trapped by a cavity. In a random laser slightly above threshold. laser this role is taken over by Strong mode competition leads the multiple scattering process. to a chaotic behaviour of the No physical cavity is required to spectrum. This is associated to obtain coherent laser emission, heavy fluctuations of the intensity since the gain saturation in a that follow Lévy statistics. random laser assures second-order coherence.

References

[1] See, for instance, P. Sheng, “Introduction to Wave Scattering, [8] D. S. Wiersma, M. P. van Albada, B. A. van Tiggelen, and Localization, and Mesoscopic Phenomena” (Academic Press, San A. Lagendijk, “Experimental Evidence for Recurrent Multiple Diego) 1995. Scattering Events of Light in Disordered Media”, Phys. Rev. Lett., 74 [2] B. Mandelbrot, “The Fractal Geometry of Nature” (V.H. Freeman and (1995) 4193. co.) 1977. [9] S. John, “Electromagnetic Absorption in a Disordered Medium near a [3] R. Metzler, A. Chechkin, V. Gonchar and J. Klafter, “Some Photon Mobility Edge”, Phys. Rev. Lett., 53 (1984) 2169. fundamental aspects of lévy flights”, Chaos, Solitons and Fractals, 34 [10] P. W. Anderson, “The question of classical localization: a theory of (2007) 129. white paint?”, Philos. Mag. B, 52 (1985) 505. [4] R. N. Mantegna and H. E. Stanley, “Stochastic process with ultraslow [11] D. S. Wiersma, P. Bartolini, A. Lagendijk, R. Righini, “Localization of convergence to a Gaussian: The truncated Lévy flight”, Phys. Rev. Lett., light in a disordered medium”, Nature, 390 (1997) 671. 73 (1994) 2946. [12] C. Toninelli, E. Vekris, G. A. Ozin, S. John, and D. S. Wiersma, [5] A. M. Reynolds, A. D. Smith, R. Menzel, U. Greggers, D. R. Reynolds, “Exceptional Reduction of the Diffusion Constant in Partially and J. R. Riley, “Displaced Honey Bees Perform Optimal Scale-free Disordered Photonic Crystals”, Phys. Rev. Lett., 101 (2008) 123901. Search Flights”, Ecology, 88, no. 8 (2007) 1955. [13] D. S. Wiersma, “The Physics and Applications of Random Lasers”, [6] P. Barthelemy, J. Bertolotti, and D. S. Wiersma, “A Lévy flight for Nature Phys., 4 (2008) 359. light”, Nature, 453 (2008) 427. [14] L. Florescu, S. John, “Photon statistics and coherence in light [7] S. Feng, C. Kane, P. A. Lee, and A. D. Stone, “Correlations and emission from a random laser”, Phys. Rev. Lett., 93 (2004) 013602. Fluctuations of Coherent Wave Transmission through Disordered Media”, Phys. Rev. Lett., 61 (1988) 834.

Diederik Wiersma He is researcher at the European Laboratory for Non-linear Spectroscopy (LENS), Università di Firenze, and of the Istituto Nazionale di Fisica della Materia (INFM-CNR), in Italy. He is leading a research group that deals with photonic materials on micro and nano meter length scales. His group has played a leading role in the understanding of light transport in periodic, quasi-crystalline, and disordered structures, including the observation of phenomena like light localization, Bloch oscillations of light, and random lasers. The group has also developed a patented technology to realize re-writable photonic circuits with a unique liquid infiltration technique. Recently the group was the first to observe the optical analogy of Lévy flights and super diffusion of photons in a newly developed material called Lévy glass.

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Electronic and transport properties of pristine graphene nanoribbons

Alessandro Cresti* CEA, LETI-Minatec and Institute for Nanoscience and Cryogenics, INAC/SPSMS/GT Grenoble, France

After its experimental discovery in 2004, graphene has emerged as a novel and promising material for future microelectronics. Its unusual electronic and transport properties make it an extremely interesting object from both a fundamental perspective and an applicative perspective.

1 Graphene: a wonderland in a pencil tip viewpoint of production of plane graphene monolayers, this constitutes the foremost drawback of the technique. Graphene is a monolayer of carbon atoms packed into a Geim and co-workers [1] first succeed in producing and two-dimensional honeycomb lattice and can be considered isolating single layers of graphene in 2004. Their technique as the mother of other carbon materials with different consists in rubbing the surface bulk graphite, thus generating dimensionalities. In fact, by packing graphene sheets we a certain amount of flakes, among which monolayers of obtain the three-dimensional bulk graphite, by cutting a graphene. These sheets are almost invisible under an optical layer into one-dimensional strips we have nanoribbons microscope. To solve this problem, it is necessary to deposit and if we roll them we build nanotubes, by cutting out the flakes on a silicon wafer with a 300–350 nm thick silicon zero-dimensional structures and alternating pentagons oxide substrate. This critical value of the thickness allows one and hexagons, we obtain fullerenes, see fig. .1 As in the to observe the sheets thanks to the interference-like contrast case of fullerenes, dirty graphene multilayers are produced with respect to the empty wafer. A further selection of the spontaneously in natural processes, as combustion, or simply monolayers can be performed by atomic force microscopy by writing on a paper with a pencil. However, due to the or Raman spectroscopy. The latter has proved to be an difficulties in its identification, only recently experimentalists extremely efficient method to investigate the thickness of have isolated graphene monolayers and have developed the graphene sheets and allows one to identity monolayer, efficient techniques to obtain and pick them out in a bilayer and up to five layers. This mechanical cleavage laboratory. technique is widely employed by experimentalists thanks to its low cost and relative simplicity. However, it is not suitable 1.1 Fabrication techniques for mass production in view of industrial applications. The first attempts to produce graphene from bulk graphite The idea of growing graphene directly on a substrate is were based on chemical exfoliation. After the intercalation interesting for the potential applications in microelectronics. Epitaxial graphene is obtained, for example, by chemical of potassium graphite (KC8) into highly oriented pyrolytic bulk graphite, the intercalated compounds are removed vapor deposition of hydrocarbons on metal surfaces, but chemically. This mechanism leads to exfoliation of graphene quality and continuity of these layers are still unknown. sheets, which soon scroll thus giving rise to carbon Another technique is the thermal decomposition of nanoscrolls rather than planar graphene sheets. From the silicon carbide [2]. A silicon carbide crystal is heated to a temperature between 1250 and 1450 celsius degrees. Consequently, silicon desorbs and ultrathin epitaxial * e-mail: [email protected] graphene layers develop. The growing process is monitored

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by the low-energy electron diffraction technique and the result is analyzed by AFM and STM microscopy. The main benefit of this method is that the produced material can be patterned by standard nanolithography, thus paving the way for microelectronic integration. More recently, an innovative chemical technique developed by Dai and co-workers [3] allowed to obtain long and narrow graphene nanoribbons.

1.2 Properties of two-dimensional graphene As shown below, two-dimensional graphene turns out to be a semimetal with linear dispersion around the Fermi energy. From an applicative perspective, the most important feature of graphene is the high mobility of carriers, which allows, in principle, the realization of high-frequency electronic Fig. 1 From the two-dimensional honeycomb graphene lattice, we can obtain devices. From the viewpoint of physics, the carbon materials of other dimensionalities, such as 3D bulk graphite, 1D most intriguing peculiarities of graphene are nanotubes and nanoribbons, or 0D fullerenes. due to its band structure, whose properties are strictly related to the well-known electronic structure of bulk graphite [4]. The geometry of the graphene lattice can be described by_ two translation vectors_ R1= a(1/2, √3/2) and R2= a(–1/2, √3/2), where a = 2.46 Å, and two basis vectors d = (0, 0) and _ 1 d2= (0, a/√3), which identify the A-sublattice and the B-sublattice, see fig. 2(a). The first Brillouin zone is hexagonal and only two of

the six points at the corners (indicated as K+ and K–) are non-equivalent, in the sense that all the other points can be connected to one of these two by means of reciprocal translation vectors. To evaluate the energy bands, we adopt a single-orbital–per–atom tight-binding Hamiltonian. In fact, in a graphene sheet, the s, 2 px and py orbitals of the carbon atoms are sp hybridized and form strong σ and σ* bonds in the plane of the layer. The bands generated by these hybridized orbitals are far from the Fermi energy and are not involved in low-energy

charge transport. The remaining pz orbitals give rise to the π valence and π* conduction Fig. 2 (a) The graphene honeycomb lattice can be described by two translation bands. In the low-energy transport, only the vectors R1 and R2 and two basis vectors d1 and d2, which identify the A and B sublattices. (b) The energy bands touch at the corners of the hexagonal first electronic states arising from these pz orbitals Brillouin zone, where the energy dispersion is linear and assumes the shape of are important. We can thus consider a single- electron-like and hole-like cones (c). orbital tight-binding Hamiltonian with zero site energy and t = –2.7 eV hopping energy.

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Fig. 3 Veselago lens: when passing from electron-like particles to hole-like particles, the opposite mutual orientation of group velocity and wave vector in the two regions entails a negative refractive index and allows focusing of electron beams.

Fig. 4 (a) Armchair graphene nanoribbon made up of N dimer lines. The primitive cell contains 2N atoms, N belonging to the A-sublattice and N belonging to the B-sublattice. (b) Coupled chains equivalent to the Hamiltonian of the system when expressed on the Bloch sums basis. (c) Energy bands of a W ≈ 75 nm wide ribbon in the absence of magnetic field. (d) Enlargement of the band structure around k = 0 for a 611-aGNR. The system is gapless and the energy dispersion is linear close to the CNP. (e) Enlargement of the band structure around k = 0 for a 610-aGNR. In this case, we observe an energy gap, whose value is inversely proportional to W. (f) Energy bands of a W ≈ 75 nm wide ribbon in the presence of B = 10 T magnetic field. (g) Enlargement of the band structure aroundk = 0. The sequence of Landau levels as well as the bending of the bands in correspondence of the edge states is clearly visible. (h) Semiclassical picture of the formation of bulk Landau levels and edge states.

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Because of this choice, the Fermi energy is now set to zero. 2 Electronic properties of nanoribbons We can evaluate the eigenvalues of the Hamiltonian corresponding to the wave vector k, by making use of the A graphene nanoribbon (GNR) is a stripe of graphene with Φ Φ Bloch sums A(k) and B(k) on the two sublattices. The width W along the y-axis and infinitely extended along the result is x-axis. Two possible edge terminations identify armchair nanoribbons (aGNRs) and zigzag nanoribbons (zGNRs), as reported in fig. 4(a) and fig. 5(a). An aGNR can be considered (1) . as composed of a certain number N of dimer lines; we denote it as N-aGNR. The corresponding width_ is W=(N – 1) a/2 and As clearly visible in fig. 2(b), the valence and conduction the length of the primitive cell is b =√3a/2. In a similar way, a bands touch at the corners of the first Brillouin zone, in zGNR constituted of N zigzag_ lines is denoted as N-zGNR, its correspondence of the Fermi energy at the charge neutrality width is W=(3N – 2) a/(2√3) and the length of the primitive point (CNP). The electrons with positive energy are classified cell is a. Depending on the experimental conditions, many as electron-like particles, the electrons with negative energy different chemical groups can passivate the dangling bonds as hole-like particles. Around the CNP, the energy dispersion of the carbon atoms at the edges. Usually, the samples is linear and forms energy cones as for massless relativistic undergo a heating process at high temperature and low particles, see fig. 2(c). This analogy is further strengthened by pressure followed by hydrogen exposure. Therefore, we can expanding the k-dependent Hamiltonian_ around the assume hydrogen passivation at the edges. This allows us to π π K+= (2 /a) (2/3, 0) and K–= (2 /a) (1/3, √3/3) points. In fact, adopt a single-orbital Hamiltonian with a reasonable degree if we consider, for example, the K+ point and introduce of accuracy. Φ+ [Φ Φ the vector (k) = A(K++k), B(K++k)], the linearly approximated Hamiltonian turns out to be 2.1 Armchair nanoribbons Let us start by evaluating the energy bands of an aGNR. Since (2) σ , the ribbon is periodic along the x-direction, we can make _ use of the 2N Bloch sums corresponding to the N atoms σ σ σ σ γ 3/(2 where = ( x, y, z) are the Pauli matrices and =a|t|√ ħ). belonging to the A-sublattice and the N atoms belonging to This Hamiltonian is exactly the Dirac Hamiltonian for massless the B-sublattice, see fig. 4(a). If we order the basis as particles with spin ½, where the light velocity is replaced by (A1, B2, A3,…, AN–1, BN, B1, A2, B3,…, BN–1, AN), the resulting γ and the two components of Φ+(k) correspond to the so- k-dependent Hamiltonian turns out to be called pseudospin degrees of freedom. From this perspective, electron-like and hole-like particles can be seen as particles and antiparticles. Far away from the Dirac points, the dispersion is no more linear and the so-called trigonal warping takes place. In order to account for this effect, higher-order (3) , terms must be included in the Hamiltonian (2). The deep analogy with the Dirac Hamiltonian has given hope to observe relativistic quantum electrodynamics phenomena at the extremely low energies of a typical semiconductor material. Among them, we mention the Klein paradox: due to the gap absence and the linear dispersion particles can where exp [(–1)n–1ikb/2]. The Hamiltonian is made up of four easily tunnel very high potential barriers. In fact, once inside N × N blocks: the two diagonal blocks are tridiagonal matrices the barrier region, electrons turn into hole-like particles thus with 0 diagonal elements and t off-diagonal elements, the enabling tunneling. Another very interesting prediction, with off-diagonal blocks are diagonal matrices with alternating possible technological applications, is the electron focusing t exp (± ikb/2) elements. Formally, H is equivalent to the effect of Veselago lenses [5], seefig. 3. When an electron- Hamiltonian of two coupled chains with N orbitals and first like carrier turns into a hole-like carrier, for example in the neighbor interactions, see fig. 4(b) . The onsite energy is zero, presence of a potential barrier, the relative directions of group the intrachain hopping parameter is t and the interchain velocity and wave vector become opposite. As a consequence, hopping parameters are t exp (± ikb/2). By diagonalizing this the velocity component parallel to the barrier changes its sign, Hamiltonian, we obtain the energy bands reported in fig. 4(c). thus entailing a negative refractive index. By designing the Notice that the Dirac points of 2D graphene are now folded shape of the potential barrier properly, it is possible to focus into k = 0. This is due to the armchair termination and can electrons in the same way optical lenses focus light beams. be understood by projecting the graphene band structure

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Fig. 5 (a) Zigzag graphene nanoribbon made up of N zigzag lines. The primitive cell contains 2N atoms, N belonging to the A-sublattice and N belonging to the B-sublattice. (b) Chain equivalent to the Hamiltonian of the system when expressed on the Bloch sums basis. (c) Energy bands of a 353-zGNR (W ≈ 75 nm) in the absence of magnetic field. (d) Enlargement of the band structure around the Dirac point. The system is gapless and a double-degenerate almost flat band extends from the Dirac points atk = 2π/(3a) to the boundaries of the Brillouin zone. (f) Energy bands of the same ribbon in the presence of B = 10 T magnetic field. (g) Enlargement of the band structure close to the Dirac point. The sequence of Landau levels as well as the bending of the bands in correspondence of the edge states are clearly visible.

(1) on the armchair orientation axis of the Brillouin zone. More sophisticated ab initio calculations have shown that N-aGNRs are metallic if N = 3m + 2, where m is an integer actually an energy gap is always present and thus metallic number, see fig. 4(d), while in the other cases the ribbons are aGNRs do not exist. Moreover, the hierarchy of the energy semiconductor with a gap inversely proportional to the width gaps (4) is changed. From the tight-binding point of view, W, see fig. 4(e). We can explain this behavior by considering a variation in the edge hopping parameter due to edge that, at k = 0, the coupled chains turn into a two leg ladder distorsion and a three-nearest neighbors model can mimic with N rungs and hopping parameters all equal to t. The the shape of the energy bands around the CNP quite eigenvalues of this system are analytically known and give accurately. a gap We can take into account the presence of a homogeneous and perpendicular magnetic fieldB by means of the Peierls factors, i.e. by assigning the hopping elements of the ribbon (4) Hamiltonian a phase that is proportional to the magnetic flux Φ B through each hexagonal plaquette of the honeycomb lattice. By choosing a proper gauge for the vector potential, ∆ ∆ ∆ with N=3m > N=3m+1 > N=3m+2 = 0. The same results can the Hamiltonian preserves its invariance under translations be obtained by solving the Dirac equation with the proper along the x-axis. Hence, we can still adopt the k-dependent boundary conditions to describe the presence of the edges. Bloch sums as a convenient basis for the diagonalization.

20 < il nuovo saggiatore A. cresti: electronic and transport properties of pristine graphene nanoribbons

Because of that, the interchain hopping parameters of the we easily obtain the energy bands, as reported in fig. 5(c) equivalent two coupled chains acquire an n-dependent for a 75 nm wide 353-zGNR. It is worth highlighting some phase: peculiar features of the band structure: i) there are two valleys with almost linear dispersion close to the CNP, they (5) are located around k = ± 2π/(3a), where the Dirac points of two-dimensional graphene are folded; ii) at k = ± 2π/(3a) α πΦ Φ where = 2 B / 0 is proportional the ratio between the the levels are equispaced, with a separation inversely Φ Φ magnetic flux B and the elementary magnetic flux 0= hc/e. proportional to the width of the ribbon; iii) there is high The effect of the magnetic field on the electronic structure is degeneracy at the borders of the Brillouin zone, where E = ± t; quite considerable, as evident in fig. 4(f, g) for a 75 nm wide iv) there is a double degenerate almost flat band that extends 611-aGNR with B = 10 T. First of all, we observe the formation from the borders of the Brillouin zone to the Dirac points. of flat Landau levels (LLs). As predicted by the Dirac equation It is possible to understand all these features by analyzing with mimimal substitution for the magnetic_ field,_ LLs are the equivalent system of fig. 5(b) in detail. For example, at π/ double degenerate and distributed as En~ √B √n. In contrast the borders of the Brillouin zone, we have cn(k = ± a)=0, to the case of ordinary two-dimensional electron gases, i.e. the linear chain splits into two isolated sites at the edges LLs are not equispaced and do not depend linearly on the and N – 1 couples of dimers. All the dimers have eigenvalues magnetic field. Moreover, there is a double degenerateE = 0 E = ± t, and this explains the high degeneracy at k = ± π/a. level, which is shared by electon-like and hole-like particles. The two isolated sites correspond to a double degenerate This peculiar feature leads to the experimentally observed E = 0 state which is located exactly at the edges of the ribbon, half-integer quantum Hall effect [6],i.e. the quantization of and gives rise to the two almost flat bands. As predicted by the magnetoconductance as the Dirac equation, the wave function of these states decays exponentially from the edges to the bulk, with an exponent (6) . that depends on k linearly. At the Dirac points we have c (k = ± 2π/(3a)) = 1/2, i.e. all the We also observe that the energy bands bend as we move hopping parameters of the equivalent linear chain are now away from k = 0. This phenomenon is due to the finite equal to t. From the literature, we know the eigenvalues of transverse extention of the ribbon. In fact, the average such a Hamiltonian. For large ribbons and close to the CNP, position of the eigenstates is stricly related to their the relation wave vector, and it turns out that states at the edges of the Brillouin zone are also located at the edges of the (8) nanoribbon. As a consequence, their energy increases since, in a semiclassical picture, the cyclotron orbits cannot be holds, where n = 0, ±1, ±2, ... .Therefore, as numerically completed due to the presence of the walls (skipping orbits), observed, the first levels around the CNP are equispaced and as schematically shown in fig. 4(h). This also explains why, to the spacing ∆ ≈ |t|π/(N+1/2) is inversely proportional to the observe LLs, it is necessary to consider ribbons broader than zGNR width. the magnetic length, that is some tens of nm for reasonable As for aGNRs, ab initio calculations predict some changes magnetic fields. in the band structure. In particular, the almost flat bands become more dispersive; this can be reproduced by 2.2 Zigzag nanoribbons considering third-neighbors interactions in the tight-binding In the case of zGNRs, we can proceed in an analogous way. By Hamiltonian. Moreover, due to the spin polarizability, a small ordering the Bloch sums basis as (A1, B1, A2, B2, A3,…, AN, BN), gap opens. we obtain the tridiagonal k-dependent Hamiltonian In the presence of a homogeneous perpendicular magnetic field, the alternating hopping parameters acquire a phase factor

(7) (9) .

As clearly visible in figs. 5(e, f), a strong magnetic field with cn(k) = c(k) = cos (ka/2). This Hamiltonian corresponds induces LLs and magnetic edge states in correspondence of to an equivalent system composed of a linear chain with 2N the two valleys and all the considerations regarding aGNRs sites and first-neighbor interactions, which are given byt are still valid. Notice that the double-degenerate almost and 2tc(k) alternately, see fig. 5(b). By direct diagonalization, flat levelE = 0 now corresponds to magnetic bulk states, or,

vol24 / no5-6 / anno2008 > 21 scienza in primo piano depending on the strength of the magnetic field, to a mixture Thus, in spite of its ballistic nature, the system displays an σ 2 π of magnetic bulk states and non-magnetic edge states. In ohmic behavior with minimum conductivity min = 4e /(h ) contrast to the case B = 0, at the borders of the Brillouin zone and Fano factor 1/3, as in the case of a diffusive conductor. c (k = ± π/a) ≠ 0, thus we do not recover the high degeneracy That is why we talk about “pseudodiffusive” regime. Let us of the energy levels. now consider an equivalent system consisting of a zGNR with a superimposed potential barrier of height V, length L and width W, as reported in fig. 6(a). Experimentally, one can 3 Transport phenomena in pristine nanoribbons induce such a potential barrier, for example, by means of a In this section, we investigate some peculiar aspects top gate. If we fix the energy of the injected electronsE just of electronic transport in clean GNRs. Namely, the above V, many bands, i.e. conductive channels, are active “pseudodiffusive” regime, the switching effect due to GNR in the leads, while the gated region is very close to the CNP. specific geometry and the possibility of manipulating Consequently, the electronic transmission is mainly sustained currents in the presence of high magnetic fields. These by tunneling through evanescent modes. In fig. 6(b) and fig. phenomena originate from different intrinsic properties of 6(d), we report conductance and Fano factor as a function graphene, as the Dirac-like energy dispersion, the spatial of the length L, in the case of N-zGNRs with N = 280, 290,…, symmetry of the GNRs and the electron/hole-like character 470 (corresponding to W ≈ 60–100 nm), V = 0.5 eV and of the charges. We interpret them with the help of the E = 0.501 eV. All the conductance curves have a similar Green’s function formalism, which allows us to obtain global behavior and, for very long L, they reach the limit value G transport and electronic properties, as conductance, Fano =2e2/h. In this situation, it is the single active band in the factor and density-of-states, as well as local quantities, as gated region that sustains transport, while tunneling through microscopic current distribution and local density-of-states. evanescent states is fully quenched. For what concerns the Fano factor, in certain ranges of L and for all the considered 3.1 “Pseudodiffusive” transport regime Ws, it keeps the predicted value around 1/3. The conductivity Experimental and theoretical works agree on the existence σ = GL/W and the Fano factor F as a function of the ratio of a finite minimum conductivity of graphene, measured L/W are shown in fig. 6(c) and fig. 6(e), respectively. All the at the CNP. However, the universality of its value is still curves almost collapse into a single one, thus indicating L/W heatedly debated in the literature. Several factors, as the as the proper scaling parameter. Moreover, the conductivity σ 2 π short- or long-range nature of the disorder and the electron- assumes the expected value min= 4e /(h ) when 0.1 < L/W electron interaction, play a crucial role in this issue. Here, < 0.4. This confirms that for clean, short and wide GNRs we we illustrate the case of clean graphene, which, under expect to observe the “pseudodiffussive” transport regime. particular conditions, exhibits a minimum conductivity equal Similar results have also been confirmed by other tight- to 4e2/(hπ). Consider an L-long and W-wide GNR at the CNP, binding calculations and, as long as we are close to the CNP, between two ohmic contacts constituted of highly doped they have been proven to be independent of the specific graphene leads. The transmission properties of this system geometry and nature of the leads. Some recent experimental were investigated in the case of short and wide GNRs (L < W), works seem to validate the theoretical predictions in the with a large number M of active conductive modes in the case of exfoliated graphene samples. In particular, minimum σ 2 π leads. By making use of the Dirac equation with hardwall conductivity min= 4e /(h ) and Fano factor F = 1/3 were confining potential for the description of the ribbon edges, observed in very wide and short GNRs, where the effect of the the transmission coefficients of the different conduction (rough) edges can be neglected. channels turn out to be [7] 3.2 Even-odd effect (10) In the presence of a low potential step and close to the charge neutrality point, the transmission properties of an with n = 0, ±1, ±2, ... .Analogous results hold for smooth N-zGNR depend on the even or odd number N of chains confining potentials. In the limitM >>W/L → ∞, the composing the ribbon. Before describing and analyzing conductance G and the Fano factor F (the ratio between shot- this phenomenon, let us note that N-zGNRs with even N noise and Poissonian noise) are are invariant under a mirror reflection with respect to a plane perpendicular to the zGNR and passing along its axis, see fig. 7(a). If N is odd, zGNRs are invariant under a glide symmetry operation, which consists of the mirror reflection (11) plus a fractional translation along the ribbon axis, see . fig. 7(b). We can thus classify the eigenfunctions of the tight-

22 < il nuovo saggiatore A. cresti: electronic and transport properties of pristine graphene nanoribbons

binding Hamiltonian according to their even or odd parity with respect to the symmetry operation that corresponds to the zGNR under investigation. By simple considerations, we can see that all the eigenfunctions that correspond to the same energy bands in the zGNR electronic structure, have the same parity. Moreover, the parity of adjacent energy bands is opposite thus constituting a sequence of alternate parity modes, as represented in fig. 7(c) with different colors (magenta and green). In particular, the two electron-like and hole-like bands close to the CNP have opposite parities. Let us now consider the effects of a superimposed (sharp or smooth) potential step with height V, as reported in fig. 7(c). If the potential rises along the ribbon axis direction x and is independent of y, the (mirror) symmetry invariance is preserved by the step for even N, while the (glide plane) symmetry invariance is not preserved for odd N. In this latter case, if we inject an electron from the right side along electron conductive modes, it will be transmitted to the left side of the GNR as a hole-like particle. In fact, though the parity of the bands involved in transport is different on the two sides, transmission is allowed because the potential step mixes states with different parity. In fig. 7(d), we can see the conductance of a 71-zGNR as a function of the energy for V = 0.05|t| and for the smooth (blue) and sharp (red) potential profile. The conductance displays a typical step-like behavior which can be easily understood by considering the number of active energy bands on the two sides of the system at different energies (see the colored regions in fig. 7(d) and the corresponding energy ranges in fig. 7(c)). It is worth noting that, in the (magenta) region Fig. 6 (a) Configuration of the system for the study of the pseudodiffusive 0 < E < V, G is perfectly quantized in the case transport regime: a very short and broad barrier of length L and width W is of the smooth potential, while it shows a dip superimposed to the zGNR. The barrier height V is very high and the electrons when the potential is sharp. To understand are injected with energy E ≈ V. The region of the barrier is thus close to the charge neutrality point and many incoming and outcoming conductive this behavior, consider an electron injected channels are active. (b) Conductance for V = 500 meV, E = 501 meV, in the range from the right with energy 0 < E < V. It enters W ≈ 60–100 nm (from bottom to top), as a function of L. (c) Conductivity σ the system on a mode belonging to the first as a function of the ratio L/W for the same data. All the curves collapse into a electronic band on the left valley, where single one and for 0.1 < L/W < 0.4 the conductivity assumes the predicted value σ = 4e/(hπ). (d) Fano factor as a function of L. (e) Fano factor as a function of the slope of the energy band is negative, i.e. L/W. For short and broad ribbons, the Fano factor assumes the predicted the group velocity is directed from right to value 1/3. left. When the electron crosses the barrier and enters the left region, the transmission takes place along a mode on the right

vol24 / no5-6 / anno2008 > 23 scienza in primo piano valley, where the slope of the first hole-like band is negative. Thus, in this energy range, transmission requires scattering from the left to the right valley. In the case of the smooth potential step the scattering process takes place adiabatically, i.e. with variations in k of the order of 1/∆, where ∆ is the length along which the potential rises (in our case ∆ = 6 nm). Consequently, when crossing the barrier, electrons move from the left valley to the right valley smoothly, without backscattering. On the contrary, in the case of sharp potentials, the backscattering process is not quenched since the Fourier transform of the potential contains a wide range of frequencies. In the case of even indexed zGNRs, the conductance shows a gap in the region 0 < E < V, independently of the smoothness of the potential, as reported in fig. 7(e) for a 72-zGNR. In this case, the potential preserves the mirror symmetry of the ribbon, thus forbidding any scattering between states with opposite parity. This even/odd or valley-valve effect was first observed and explained in terms of edges states and Dirac equation. Here, we illustrate a symmetry-based explanation, which is completely general and independent of the Dirac-like behavior of the electrons. The interest in this effect is testified by the publication of several papers on the subject, with the hope of realizing controllable gaps in GNRs. However, instability of zigzag ribbons and extreme sensitivity to the number of chains N make an experimental realization of such a system rather hard to achieve.

3.3 Current manipulation As seen in sect. 2, a high magnetic field in large enough GNRs gives rise to the formation Fig. 7 (a) N-zGRNs with N even are invariant under reflection with respect to a of Landau levels and magnetic edge states. plane perpendicular to the ribbon and passing through its axis (mirror symmetry). In the case of zGNRs, we already noted that (b) In the case of odd N, the symmetry operation consists of the mirror reflection followed by a fractional translation of half lattice constant along the ribbon axis electronic-like edge states on the right side of (glide plane symmetry). (c) Energy bands in the presence of a (sharp or smooth) the valleys are located along the upper edge of potential step with height V. The bands have even or odd parity with respect to the ribbon, while states on the left side of the the symmetry operation of the corresponding ribbon. The alternating parity of the eigenstates corresponding to the two bands is indicated with different colors valley are located along the lower edge. The (green and magenta). If the potential step varies only along the x-direction, then opposite occurs for the hole-like bands. On it is invariant under the mirror symmetry operation, while it does not preserve the the two sides of the valley, however, also the glide plane symmetry. (d) Conductance of a 71-zGNR in the presence of a sharp slope of the energy bands with respect to k is (red) / smooth (blue) step with V = 0.05|t|. The different colored energy regions correspond to those reported in (c). (e) The same for a 72-zGNR. In this case, we opposite, i.e. the group velocity has different observe a gap with width V. directions, see fig. 8(a). Consequently, electron- like particles injected from the right to the left can only flow along the lower edge, while

24 < il nuovo saggiatore A. cresti: electronic and transport properties of pristine graphene nanoribbons

Fig. 8 (a) Band structure of a 353-zGNR in the presence of a 10 T magnetic field. If we inject electrons from the right side of the ribbon with energy E = 125 meV, they will propagate as electron-like particles along the three conductive modes indicated by blue circles. If electrons are injected at E = –125 meV, they will propagate as hole-like particles along the three conductive modes indicated by red circles. (b) Profile of transport spectral currents along a transverse section of the ribbon in the case E = 125 meV (blue line) and E = –125 meV (red line). Due to the different spatial chirality, particles flow along opposite edges when injected from the right. (c) Scheme of the energy bands and spatial spectral current distribution in the case E = 50 meV and V = 25 meV. The step is at x = 0, in correspondence of the black dashed line. Since they keep their electron-like nature, particles are transmitted along the lower edge. Due to the low height of the potential step, no backscattering takes place in this case. (d) The same for E = 50 meV and V = 100 meV. When crossing the potential step electrons turn into hole-like particles. Therefore, they are transmitted along the upper edge and partially backscattered along the upper edge. Injected, transmitted and backscattered currents and corresponding involved modes are indicated by black, blue and magenta arrows, respectively.

vol24 / no5-6 / anno2008 > 25 scienza in primo piano electron-like particles injected from the left to the right can reasonable Ion/Ioff ratios, it is necessary to control and engineer only flow along the upper edge. We call this spatial separation a gap in the conductance of ribbons. This experimentally of the currents flowing in opposite direction “spatial chirality”. challenging goal is complicated by another inescapable factor In the case of hole-like particles, electrons can only flow that is disorder. Ribbons are subject to several possible sources from the right to the left along the upper edge and from the of disorder: charged impurities in the substrate, ripples on the left to the right along the lower edge. Therefore, electron- surface, functionalization of the edges, chemisorptions and like and hole-like particles have opposite spatial chiralities roughness at the edges. [8]. In fig. 8(b), we report the spatial distribution of spectral For a thorough bibliography on graphene and for a general transport currents along a transverse section of a 353-zGNR review of disorder effects, not considered in the present paper, for electron-like and hole-like particles injected from the we address the reader to refs. [9-12]. right side to the left side of the ribbon at E = ± 125 meV. The distribution of the currents along different edges confirms our prediction regarding their opposite spatial chirality and References suggests the possibility to manipulate currents by means of [1] S. Novoselov, A. K. Geim, S. V. Morozov, Jiang, Y. Zhang, an external gate. In fact, if we inject electrons from the right S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Science, with a positive energy, they will enter the system as electron- 306 (2004) 666. like particles and the corresponding current will flow along [2] C. Berger, Z. Song, T. Li, X. Li, A. Y. Ogbazghi, R. Feng, Z. Dai, the lower edge. If now we superimpose a potential step high A. N. Marchenkov, E. H. Conrad, P. N. First and W. A. de Heer, J. Phys. Chem. B, 108 (2004) 19912. enough to convert the electrons into hole-like particles, they [3] X. L. Li, X. R.Wang, L. Zhang, S. Lee and H. J. Dai, Science, 319 will be partially backscattered along the upper edge and (2008) 1229. partially transmitted along the upper edge. In practice, we [4] F. Bassani and G. Pastori Parravicini, Il Nuovo Cimento B, 50 (1967) 95. can realize a switch that directs the current along the upper [5] V. V. Cheianov, V. I. Fal’ko and B. L. Altshuler, Science, 315 (2007) or the lower edge of the ribbon selectively, by means of an 1252; J. B. Pendry, Science, 315 (2007) 1226. external gate that induces the potential step and a high [6] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, magnetic field. As an example, in figs. 8(c, d) we report the M. D. Katsnelson, I. V. Grigorieva, S. V. Dubonos and A. A. Firsov, Nature, 438 (2005) 197; Y. Zhang, Y. –W. Tan, H. L. Stormer and microscopic spectral current distribution in a 353-zGNR when P. Kim, Nature, 438 (2005) 201. the energy of the injected electrons is E = 50 meV and the [7] J. Tworzydło, B. Trauzettel, M. Titov, A. Rycerz and height of the potential step is V = 25 meV or 100 meV. In the C. W. J. Beenakker, Phys. Rev. Lett., 96 (2006) 246802. case V = 25 meV, the electrons keep their electron-like nature [8] A. Cresti, G. Grosso and G. Pastori Parravicini, Phys. Rev. B, 77 (2008) 115408. throughout the whole system. Therefore they are injected [9] A.K. Geim and K.S. Novoselov, Nature Mater., 6 (2007) 183. and transmitted along the lower edge and backscattered [10] M. I. Katsnelson, Mater. Today, 10 (2007) 20. along the upper edge. In the case V = 100 meV, electron- [11] A. Cresti, N. Nemec, B. Biel, G. Niebler, F. Triozon, G. Cuniberti and S. Roche, Nano Research 1 (2008) 361. like particles turn into hole-like particles when entering [12] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov and the left region of the ribbon and the current is transmitted A. K. Geim, Rev. Mod. Phys. in press, arXiv:0709.1163. along the upper edge. Due to the large separation between Landau levels at relatively small magnetic fields, this effect should also be visible at room temperature and might be exploited in the realization of a current switch with possible applications in quantum electronics. Alessandro Cresti After graduating (2001) and earning a PhD (2006) in physics in 4 An eye to the future the theoretical solid-state group at the Physics Department of We have illustrated some interesting electronic and transport Pisa University, the author spent two further years in the same group with the support of National Enterprise for nanoScience and properties of clean graphene nanoribbons. The Dirac-like nanotechnology (NEST), and Scuola Normale Superiore. In 2008 he nature of particle around the charge neutrality point, the moved to Grenoble, where he is currently working as a post-doc at specific spatial symmetry of the ribbons and the spatial the Commisariat à l’Énergie Atomique (LETI-MINATEC and INAC) in the group of Professor Roche. The main subject of his research is chirality in the presence of high magnetic fields determine the simulation of electronic transport in graphene-based devices by many peculiar aspects that might have several applications means of the Green’s function formalism adapted to a tight-binding under both a fundamental and an applicative perspective. framework. Besides graphene nanoribbons, his interests include From the technological point of view, the efforts aim at transport in two-dimensional gas-based devices, effects of dephasing, analysis of shot-noise in cavities. the realization of graphene-based transistors with features suitable for microelectronics applications. In order to obtain

26 < il nuovo saggiatore fisica e...

Optical tweezers and their applications

Enzo Di Fabrizio BIONEM Laboratory, University of Magna Graecia, Campus “Salvatore Venuta”, Catanzaro, Italy

An overview of the “optical tweezers” and of some of their applications is given. The physics phenomenon that gives origin to the optical trap is described and some applications to biology and the ultrasound field are presented. The importance of optical tweezers, already demonstrated in biology, biophysics and materials science can be extended to phenomena involving single molecules. Further developments can be expected in the near future when this technique will be combined with the various spectroscopies.

Introduction

In 1970 a paper titled “acceleration and trapping of particles by Radiation Pressure,” written by Arthur Ashkin [1], started the experimental activity on optical trapping. The possibility of exerting mechanical forces by photon, through radiation pressure and angular-momentum exchange, was well recognized theoretically and experimentally since the beginning of modern optics and the discovery of Maxwell equations. Nevertheless, the interest around this phenomenon remained limited because of the weakness of such forces when their effect is considered on macroscopic objects. It was the experimental skill and the scientific awareness of A. Ashkin that brought the optical trapping from a phenomenon of unpractical interest to the realm of mature and relevant cross disciplinary research field, at board of biology, physics and material science. Since 1970 a strong activity was developed worldwide whose wideness and importance can be appreciated by reading the review paper by A. Ashkin [2]. In this article we report the basic of optical tweezers, and will give few examples extracted by the research activity of different collaborating authors and groups. The intent is to try to show to the readers, eventually working in other fields, the potential of this experimental technique in several research domain.

1 Optical tweezers: physical principles

Optical forces generated by electromagnetic radiation on microscopic particles can be described in terms of momentum exchange between light and matter. By assuming light as a flow of photons carrying momentum, and considering for Fig. 1 Direction of the optical force simplicity the case of geometrical optics, when the particle size is are much bigger on the sphere as a consequence than the radiation wavelength, it is possible to explain by vector composition the of momentum conservation in ray action of optical forces on a dielectric spherical particle with a refractive index refraction. higher than the surrounding medium (fig. )1 [3]. As an effect of refraction at an

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Fig. 2 Restoring forces acting on the spherical particle for small displacements from the trap equilibrium point.

interface between two media of different refractive index, be derived according to different regimes determined by the momentum carried by a ray changes direction. Since the the ratio between the spherical object diameter, d, and the total momentum is conserved, the difference between the radiation wavelength λ. Depending on this ratio, there are initial and the final momentum is transferred to the particle. three different regimes: Rayleigh d( << λ) [4], Mie regime Figure 1 illustrates how refraction and reflection of a single (d >> λ) [3] and resonance regime (λ~ d) [5-8]. optical ray induces forces on a spherical object. Let vector p For the sake of completeness we give quantitative formulas represents the momentum of the incident light and p’, that in the ray optics regime referring to particles of µm-scale. The of the emergent light. The momentum ∆p transferred to ray optics also works in the Rayleigh limit with particles of the sphere is obtained from: p = p’ + ∆p. The difference∆ p nm-scale as described afterwards. Light can be described as between p and p’ provides the direction of the force F acting the flux of photons with momentum and energy: on the sphere by the transmitted laser beam, being F parallel to ∆p. Considering a focused laser beam, formed by a set of different rays, the total force is obtained by adding up forces exerted

by each of the rays. Optical forces generated by refraction So we can write E = pcm, where cm = c/n is the speed of light and reflections on a particle are usually decomposed on in a material with index of refraction n. If we introduce the “scattering forces” and “gradient forces”, depending on the Poynting Vector S = E × H that represents the energy flux direction parallel or perpendicular, respectively, with respect density we can write to the incoming rays’ directions [3]. Generally speaking, scattering forces contribute to push the particle in the direction of beam propagation, whereas gradient forces contribute to push the particle in the direction of the beam

intensity gradient. In particular, the relative refractive index where dA is an element of area and s is a vector of direction of the object compared to the surrounding medium, n = of S. So if we want to know the force F of light on an object O

nobject /nmedium, affects the direction of the gradient force: if we have to integrate: the relative refractive index is greater than unity, the gradient force attracts the particle towards the region of highest beam intensity, whereas in the opposite situation, the particle is pushed out of the beam.

In the case of laser beams focalized by high–Numerical– where {Sin − Sout} is the net energy flux density of the Aperture (N.A.) lenses, gradient forces are strong enough to incoming and outgoing rays. A ray of power Sin dA that hits counterbalance the action of scattering forces, so that an a dielectric object O at an angle of incidence θ causes an equilibrium point will be created in space where the particle infinite number of refracted rays of decreasing power. If will be trapped (fig. ).2 you sum the forces of all refracted rays by using the above Detailed expressions for gradient and scattering forces can equation, in the limit of Mie scattering (the size of the object

28 < il nuovo saggiatore E. Di fabrizio: optical tweezers and their applications

Fig. 3 Decomposition of optical forces into gradient and intensity force (parallel) components.

O >> λ) we obtain the total force that can be written in two components:

where θ is the angle of incidence and r the angle of refraction inside of the object. The quantities R and T are the Fresnel reflection and transmission coefficients at the surface.

Fs the scattering force points into the direction of the incident light, Fg the gradient force perpendicular to it (fig. ).3 Summing over all incident rays for example of a TEM00-mode laser beam gives the total force on the sphere. Qualitatively you find that you have two kinds of force: a resulting scattering force that tries to push away the sphere and a resulting gradient force that pulls the sphere back to the focus along the gradient of intensity. So the sphere is kept in the focus of the laser beam in all the three dimensions if the gradient force overcomes the scattering one. Practically we also have to overcome the random thermodynamic forces to hold a particle and the frictional forces to move it. It can be shown that the ratio of the q radius of the TEM00 beam and the aperture and the angle are important parameters for the gradient forces. So filling the aperture and having a big angleq cause a major force . We can find also for very small particles similar forces. For a sphere of radiusd and dielectric constant l εs we can describe the force on it in the Rayleigh limit where d << by: F = F∇ + Fs with

F∇ is a gradient force that pulls the sphere to the point of highest intensity along the gradient of |S|. Fs is a scattering force that tries to push the sphere along S (fig. 3). The other quantities ε ε p l are: the dielectric constant of the particle, 0 the dielectric constant of the medium, k = 2 / the wave number. However, in most situations this force is so much smaller than other forces acting on macroscopic objects that there is no noticeable effect. For example, we can calculate the force due to the change in momentum of light reflecting off of a mirror. In this case,S out = – Sin so

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Fig. 4 Optical setup including a ytterbium fiber laser (red line) and a helium-neon laser (green line), an expander (lens L1 and L2), LC-SLM, a telescope after the SLM (lens L3 and L4), a dichroic mirror, DM, a microscope objective, a specimen stage, a condenser, a Hg lamp, a CCD camera and a computer (PC). The tube lens, TL, is used for infinite correction.

potential well U of the gradient force is much larger than the F = 2 (n / c) ∫∫ (Sin) dA. The integral represents the total power of the light, which is usually expressed in watts. In the simple kinetic energy of the Brownian motion of the particle, that is << case of 100% reflection, the force is thusF = 2 (n / c) W , where exp (U/kBT) 1 that implies W is the intensity of the light in Watts. If all of the intensity of a 60 W light bulb were focused onto a mirror, the force due to radiation pressure would be 4 × 10−7 N. If a 1 kg mirror exerts a force on a scale of 9.8 N, the additional weight due to radiation pressure is clearly negligible. Objects for which This inequality allows to estimate the trap stability knowing this radiation pressure would be significant would have to the size a of the particle, its relative refractive index m,

weight less than 1 µg. In optical-tweezers experiments, the the laser power P and its focus size (w0) and the liquid radiation pressure is provided by laser light, while the objects temperature. to be manipulated are generally very small. Micron-sized In practical conditions a power of few mW is enough to have polystyrene spheres of uniform diameter are easily obtained a stable trap of polistirene bead of few microns size. and can be trapped using the forces described above. In the intermediate regime, where neither Mie, nor Rayleigh 1.2 Optical-tweezers setup regime can be fulfilled, a numerical analysis is necessary in The most basic optical-tweezers setup includes a laser beam order to effectively take into account the specific geometry. and a high-N.A. microscope objective. A dielectric particle In any case trapping is still possible and no substantial new near the focus will experience a force due to the transfer of phenomena occurs. momentum from the scattering of incident photons and will be pushed towards the center of the beam, if the particle’s 1.1 Trap stability index of refraction is higher than that of the surrounding Another important consideration that remains is the stability medium [3]. of the trap. Due to thermal motion, the Brownian motion, The optical trap results from the fact that the objects that are a stable trap is obtained when the trapping force is bigger trapped in the focus of the laser beam experience a restoring than that due to thermal motion. A necessary condition for force towards the center of the trap if they try to leave the ≥ high-intensity volume. stability is Fgrad / Fscatt 1. A necessary and sufficient condition for stability is that the In our optical-tweezers setup (see fig. )4 at the BioNEM (Bio-

30 < il nuovo saggiatore E. Di fabrizio: optical tweezers and their applications

Nanotechnology & Engineering for Medicine) laboratory, PCI-6133). The board has a maximum sampling rate of 2.5 M Catanzaro, Italy, we use an inverted microscope, with infinity- samples/second per channel and 14 bit resolution. Signal corrected optics, Nikon ECLIPSE TE 2000-U. The laser source acquisition is controlled via a software interface written in (red line in fig. 4) is a single-mode CW ytterbium fiber laser LabVIEW. (YLM-5 from IPG Photonics) emitting at 1064 nm, linear polarized and collimated. The output beam diameter is 1.3 Optical-tweezers calibration and force approximately 10 mm, then it is expanded (2 ×) by the lenses measurement

L1 and L2 with focal lengths f1 = −100 mm and f2 = 200 mm, Optical tweezers can be converted into a sensitive and is subsequently sent onto a LC-SLM (Liquid Crystals- micromechanical force transducer that is capable of exerting Spatial Light Modulator) (Hamamatsu X8267-15). and/or measuring forces in the pN range. This requires The SLM is an electrically addressed phase modulator using monitoring of the trapped object position with high spatial an optical-image transmitting element to couple an optically (nm range) and temporal (ms range) resolution. addressed PAL-SLM (Parallel Aligned Nematic Liquid Crystal- The starting point for this application is indeed that, in a small Spatial Light Modulator) with an intensity modulator. The region around the trapping point, optical forces (the gradient SLM exhibits high efficiency (40%) and a maximum phase forces) can be considered linearly varying with the trapped shift higher than 2π is provided at 1064 nm, over an active particle displacement, like Hook law F = − k ⋅ x, where k is trap area of 20 mm × 20 mm (768 × 768 pixels). We control it stiffness andx is the displacement. To calculate the applied with a computer (PC) sending different Diffractive Optical forces it is then necessary a precise measurement of the Elements (DOEs) which are calculated in real time with the trapped object displacement from the equilibrium position in help of a software we developed using LabVIEW (National the optical trap. Instruments). For calculation of the phases we used an One of the simplest position detection scheme is the back approach based on the spherical waves propagation and focal plane (BFP) detection method, which relies on the superposition approach. The same computer is used also for interference between forward-scattered light from the image acquisition, using a 2 Mpix CCD camera from Nikon. trapped object and unscattered light [9]. The interference A telescope with 0.5 × magnification, made of two plano- signal can be monitored using QPD positioned at a plane convex lenses (L3 and L4) with focal lentghs f3 = 400 mm and conjugate with the BFP of the microscope condenser. This f4 = 200 mm, is used to image the calculated DOE on the back scheme requires precise calibration of the QPD response to focal plane (BFP) of the microscope objective. the trapped particle displacement and this is usually done The beam is finally directed (reflected) into the objective exploiting the statistical analysis of the Brownian motion of (Nikon Plan Apochromat 60 ×, 1.4 N.A., oil immersion, or the particle in the optical trap. Nikon Plan Apochromat 100 ×, 1.3 N.A., oil immersion) with When a bead of known radius is trapped, the physics of an IR dichroic mirror, DM. The mirror allows the visible light Brownian motion in a harmonic potential is described by a used for illumination to pass through. known power spectrum sx. For the thermal fluctuations of a The particle movements in the optical trap can be monitored trapped object is given by by the back focal plane interferometry method. A low power laser beam generated by a 633 nm He–Ne (JDSU 1125/P) (1) is sent to the sample collinear with the trapping beam. The microscope condenser (N.A. = 0.5) collects the rays emerging which is a Lorentzian, where kB is the Boltzmann constant, T is from the sample plane and, if there are source scatterers the absolute temperature and fc is a roll-off frequency given in or near the focus, scattered light interferes with the by non-scattered light. As a result, an interference pattern is registered in the condenser BFP which is strongly dependent (2) on the relative position of the trapped object and the laser focus. To track particle movements, the BFP interference where k is the trap stiffness andγ is the drag coefficient: pattern is imaged, using a plano-convex lens (L6) with focal length f = 50 mm, onto a four-quadrant photodiode (QPD) (3) (Hamamatsu PD C5460SPL) connected to a high-speed amplifier giving a 850 kHz detection bandwidth. with η the medium viscosity and r the particle radius. A short pass dichroic filter (F2) is used to prevent the trapping This power spectrum can be fit [10,11] and the trap stiffness laser to reach the QPD. (k) can be calculated if the drag coefficient of the particle is The analog signals are digitized employing an analog- known. to-digital acquisition board (DAQ) (National Instruments, As an example, a polystyrene bead with 1 µm diameter was

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Fig. 5 A plot of the position-sensitive detector voltage output Fig. 6 Power spectral density of the trapped bead movements due to corresponding to the amplitude of displacement (in one dimension i.e. thermal motion is displayed as the dotted line. The line represents the x-axis) of a trapped bead relative to the centre of the trap. Lorentzian fit.

trapped and the QPD output signal, representing the agitation due to the Brownian motion of the trapped bead, was acquired. Figure 5 shows a plot of a measured signal amplitude. Each particle tracking was acquired for two seconds with a sampling rate of 200 kHz and this measurement was repeated at least five times for the same trapped bead. This acquisition sequence was then performed at different laser power. Each of the data sets were Fourier transformed (DFT). The squared amplitudes of the various transformed data were averaged to obtain a power spectrum for each of the different laser power. Figure 6 shows the power spectra corresponding to the measurement of fig. 5. The corner frequency was then determined by fitting the power spectrum to a Lorentzian curve

as fc=851 Hz and this value was used to obtain the trap stiffness at the selected power of the trapping laser beam (in this case, 16 mW at the sample). Using expressions (2) and (3):

where the dynamic viscosity is that of water at 300 K, η = 8.9 × 10−4 Pa·s and r = 0.5 µm. As an alternative to the power spectrum method for the trap stiffness calibration, the autocorrelation method can be used [12]. Considering the Brownian motion of a particle in the harmonic potential of the optical trap, the autocorrelation function for displacement in the x-direction g (t) = 〈x (τ + t) x (τ)〉 is determined as

(4)

where ω is the exponential decay factor given by

Therefore, the trap stiffnessk can be retrieved starting from the same set of particle displacement measurements acquired for the power spectrum method. Indeed, after calculation of autocorrelation function for the measured data (see fig. )7 and fitting with eq. (4) we can retrieve the exponential decay factor (ω = 4926 rad/s in this case) and finally we

32 < il nuovo saggiatore E. Di fabrizio: optical tweezers and their applications

Fig. 7 Semilog-plot of the position-versus-time autocorrelation for the Fig. 8 Measurement of the stiffness of the optical trap along thex -axis at same sample as being used in fig. .3 The black line represents the fit different laser powers. according to eq. (4).

obtain k = 41.3 pN/µm. DNA linkage is slightly modified from Perkins [15]. Twoµ m Then the stiffness of the optical trap for increasing laser streptavidin-coated polystyrene beads (Polysciences ltd.) powers (from 8 to 80 mW) is retrieved and a linear fit of the are linked to a lambda DNA with biotin modified ′5 -ends to stiffness values along thex -axis is shown in fig. .8 It can be obtain one DNA molecule for each bead. The protocol starts observed, as expected from theory, a linear dependence with the modification at one end (sticky end) of the lambda between the stiffness and laser power. Several papers can DNA with a complementary synthetic oligonucleotide be found in the literature, where force measurements are carrying a biotin and a phosphate on each end (5′-P- applied to extract quantitative information on internal GGGCGGGCGACCT-bio-3′). Ten µl of 17 nM lambda DNA structure of cells [13] and biochemistry of single-molecule solution are incubated with 10 µl of 1 µM oligonucleotide reactions[14]. solution in a suitable buffer and heated at 65 °C for 5 min to denature lambda DNA sticky ends. The solution is left to reach room temperature in the heating block and the ligating 2 Interdisciplinar applications enzyme, T4 DNA ligase, is added. Ligation occurs overnight at 16 °C. Purification by desalting spin columns follows to 2.1 Fluorescence microscopy in beads and DNA optical eliminate excess oligonucleotides that could compromise manipulation beads linkage step. Electrophoresis in agarose gel 0.7% at Recently DNA has not only been regarded as a biological 30 mA is carried out overnight to assess the integrity of the molecule but also as an engineering material. In fact due to DNA chain (a polymer of such a length is prone to rupture its nanometric structure (2 nm diameter) and its “intelligent” and/or entanglement) and for quantification of recovered building ability, thanks to base pairing, DNA is of considerable material after desalting. In the next step, beads are incubated interest to nanotechnology. Laser trapping of particles linked overnight at 1:10 bead/DNA molecule in phosphate buffer to long DNA molecules (e.g., lambda DNA) is quite often used pH 7.4 with gentle shaking. We found this ratio proper to link as manipulating tool in microscope imaging [15]. only one DNA each bead. After three hours settlement and Phage Lambda DNA (GenBank/EMBL accession numbers further precipitation in microcentrifuge at 1000xg for 20 min, J02459, M17233, M24325, V00636, X00906) is a linear double- the bead/DNA complex is suspended again in a phosphate stranded (48502 nucleotides) chain with 12 base pairs (bp) buffer solution containing 8% (w/w) glycerol at different NaCl single-stranded complementary 5′-ends isolated from the molarity depending on polymer contour length desired [16]. temperate Escherichia coli bacteriophage lambda. A wide-field fluorescence system using a Hg lamp for A very reliable method to link nucleic-acid molecules to many excitation is combined to our optical-tweezers setup, as substrates is the non-covalent streptavidin/biotin affinity shown in fig. .9 The excitation band can be selected, using linkage. In our laboratory the current protocol for bead- interchangeable filter sets.

vol24 / no5-6 / anno2008 > 33 Fig. 9 Schematic of optical manipulation setup combined Fig. 10 Lambda DNA linked to beads. (a-i) Represent fluorescence with fluorescence microscopy. OBJ: microscope objective, microscopy images. Arrows indicate lambda DNA filaments. DM: dichroic mirror, FF: fluorescence filter, HL: halogen lamp.

Fig. 11 Schematic figure of the confocal and trapping combination setups. Red beam is the trapping laser, the green line is the laser used for imaging. DM: dichroic mirror, OBJ: microscope objective, SLM: spatial light modulator.

Images of fig. 10a-f show an experiment where the optical 2.2 Confocal microscopy combined with OT trap is used to manipulate a lambda DNA (indicated with A confocal imaging system is also combined with our optical arrows) linked to a bead which is attached to the coverglass manipulation setup as shown in fig. 11. Integrating confocal surface. The sequence shows that the laser traps the DNA imaging and optical trapping requires specific measures to and elongates a portion of the chain till the laser beam is avoid axial translation of the trapped object following the no longer able to trap the DNA because the elastic force is microscope objective axial scan in 3D imaging. This is done stronger than the maximum optical force. In fig. 10f, it can in our set-up by changing the trap position using different be observed that lambda DNA escapes from the trap. In phase maps on the spatial light modulator while maintaining this experiment, the lambda DNA is stained with propidium the same plane (dashed line in fig. 11) for the confocal image iodide, an intercalating dye which binding stoichiometry was acquisition. A specific software which permits suitable determined to be one dye molecule per four-to-five DNA synchronization between the confocal imaging system and base pairs[17]. the SLM has been developed. An example of 3D imaging of Notice in fig. 10g-ithat some entangled DNA segments, not a suspended and optically trapped cell is shown in fig. 12. trapped by the laser beam, maintain a linear configuration. Imaging is performed using a two-photon microscopy system

34 < il nuovo saggiatore E. Di fabrizio: optical tweezers and their applications

Fig. 12 Selective section imaging of different planes of a DHL-4 lymphoma B suspended cell using a combination of holographic optical tweezers and two-photon microscopy. FITC conjugate antibodies stain the MHC class I membrane glycoproteins of the cell.

Fig. 13 (a–b) A lamellipodium growing and pushing a trapped bead. The red cross indicates the equilibrium position inside the

optical trap. Scale bar, 2 µm. (c) The neuron force, Fneu , in the (x, y)-plane obtained from a QPD recording. Trap stiffness was 0.009 pN nm−1. (d) The force exerted by a lamellipodium showing step-like jumps. Red lines, drawn by sight, indicate presumed discrete levels. The QPD recording was subsampled and filtered at 50 Hz. After low-pass filtering, the value ofs was reduced to 0.05 pN. Trap stiffness was 0.01 pN nm−1. (e) Histogram of forces measured during collisions between lamellipodia and trapped beads. Data reflect 65 experiments, each lasting 2 min. (f) Scatter plot of force duration for the collisions shown in (e). based on a Tsunami Spectra-Physics laser source and a Nikon results show that actin polymerization is necessary for force C1 scanning head. In the image, FITC conjugate antibodies production and demonstrate that not only do neurons stain the MHC class I membrane glycoproteins of a DHL-4 process information, but they also act on their environment lymphoma B cell. exerting forces varying from tenths of pN to tens of pN. The results are reported in fig. 13a-f. 2.3 Force measurement on neurons growth In this study [13], optical tweezers were used to measure the 2.4 Optical trapping for hydrodynamic fundamental force exerted by filopodia and lamellipodia with a millisecond studies temporal resolution. It was found that a single filopodium In this study [18], it is reported the use of optical tweezers for exerts a force not exceeding 3 pN, whereas lamellipodia UCA (Ultrasound Contrast Agent) microbubble manipulation, can exert a force up to 20 pN. Using metabolic inhibitors, enabling the study of bubble dynamics with controlled it was shown that no force is produced in the absence of boundary conditions. A quantification of the acoustical and actin polymerization and that the development of forces fluid dynamical forces for the very same bubble when it is larger than 3 pN requires microtubule polymerization. These freely floating and when it is close to a boundary is therefore

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Fig. 14 (a) R-t curves of the two bubbles trapped at 8 mm distance from each other and positioned 50 mm away from the wall. The dashed curve 1 corresponds to bubble 1, the solid line 2a corresponds to bubble 2. In (b), the dashed line 2b represents the R-t curve of bubble 2 oscillating after bubble 1 has been released. The R-t curve a) is also plotted for comparison. White scalebar in pictures: 5 mm.

Fig. 15 The sample is held in a capillary (SC), attached to the OT stage (red box), is illuminated by the WL source and observed by the IM, which are attached to the SAXS stage (black box). The X-ray beam is microfocused by X-ray focusing optics (XFO) inside the SC and the scattered light is recorded by the CCD. The IR laser beam is directed onto the spatial light modulator (SLM) and its wave front shaped by diffractive optical elements (DOEs) (blue inset) to control the focus and the splitting of the beam which is then reflected to the microscope objective (MO) by the dichroic mirror DM. The laser beam is focused by the MO into the SC to form the trap. The OT stage can be moved along the three axes, as indicated by the red arrows.

feasible, provided that the initial bubble properties remain ultrasound frequency of a double- and single-bubble system unchanged in consecutive experiments. The experimental is reported. Radius-time curves are taken at 15 Mfps for two results were compared with the behavior of the very same interacting bubbles. UCA microbubble under different boundary conditions by a well-controlled positioning of individual bubble using 2.5 Microdiffraction and optical manipulation of Laguerre-Gaussian optical tweezers and by recording their liposomes ultrasound-driven oscillations with an ultrahigh-speed In this study [19] an optical-tweezers manipulation of camera. With this approach, one introduced a powerful individual micron-sized liposome samples combined with the tool for investigating how the bubble dynamics, hence study of their inner nanostructure by synchrotron diffraction the acoustical signature, changes with varying distance to experiments is shown. The validity of this technique is neighboring objects. In fig. 14a-b the dynamical response at demonstrated for clusters of multilamellar liposomes trapped

36 < il nuovo saggiatore E. Di fabrizio: optical tweezers and their applications

Fig. 16 (a-b) Multiple trapping was demonstrated in view of future more complex experiments, e.g., to investigate the reactions between different colloidal microsystems. Multiple trapping of DOPE clusters with an inverse hexagonal inner nanostructure. (a) Microscope image of the capillary with the IR-laser switched on, two laser traps are visible; (b) X-ray diffraction image of the two DOPE clusters (multilamellar vesicles), viewed in thex -direction.

Fig. 17 Sequence of six images showing a polystyrene particle trapped by the TOFT. The images are magnified through a microscope with a 10 × objective and recorded by a CCD camera. The trapped sphere scatters the light coming from the fiber probe in the infrared range, which is then captured by the CCD. The trapped particle is moved below the microscope objective: it is first moved to the right (top row), and it is subsequently moved up and to the left (bottom row). Thanks to the use of a low-magnification objective, the TOFT end can be clearly seen. The particle appears as a bright point because it strongly scatters the incoming infrared radiation used for trapping.

in single and multiple positions in the optical path of a assemblies with micron- and submicron-sized SR beams, microfocused X-ray beam and analyzed in a microscanning which will find multiple applications in third and in particular mode. In fig. 15 the experimental setup where SAXS (Small- future fourth generation SR sources. Angle-X-ray-Scattering) and OT are combined is reported. Single and multiple optical traps created by means of DOEs 2.6 Fiber optics tweezers are demonstrated for fixing the samples in scanning micro- In this study [20] one presents the design and the realization SAXS experiments with multilamellar liposomes. The high of a miniaturized single-fibre optical tweezer that is able to signal-peak–to–background ratio (> 450) for ten liposomes create a purely optical three-dimensional trap. The tweezer shows that single-liposome measurements are feasible. uses engineered fibre structures with microstructured end The results presented here have given insight into the very surfaces, and its effectiveness is demonstrated by trapping fascinating gamble field to look at single supramolecular 10 mm diameter polystyrene beads. The optical tweezer

vol24 / no5-6 / anno2008 > 37 is able to provide optical manipulation and analysis of [4] Y. Harada, T. asakura, “Radiation forces on a dielectric sphere in the microscale specimens and could be the fundamental building rayleigh scattering regime”, Optics Commun., 124 (1996) 529. [5] T. Tlusty, A. Meller and R. Bar-Ziv, “Optical gradient forces of strongly block in future integrated fibre-based devices. In fig. 17 localized fields”, Phys. Rev. Lett., 81 (1998) 1738. a sequence of six images showing a polystyrene particle [6] A. Rohrbach, E. H. K. Stelzer, ”Optical trapping of dielectric trapped by the fiber tweezer is reported. The images are particles in arbitrary fields”,J. Opt. Soc. Am.,18 (2001) 839. Calculation of the radiation trapping force for the laser magnified through a microscope with a 10× objective and [7] J. A. Lock, “ tweezers by use of generalized Lorenz-Mie theory. I. Localized model recorded by a CCD camera. In this work the trapping was description of an on-axis tightly focused laser beam with spherical combined also with fluorescence microscopy. aberration”, Appl. Optics, 43 (2004) 2532. [8] M. Mansuripur, A. R. Zakharian, J. Moloney, “Radiation pressure and the distribution of electromagnetic force in dielectric media”, Optics Express, 13 (2005) 2336. 3 Summary [9] M. W. Allersma, F. Gittes, C. F. Schmidt, “Two-Dimensional Tracking of ncd Motility by Back Focal Plane Interferometry”, Biophysics. J., 74 Since its discovery, optical-tweezers microscopy moved (1998) 1074. [10] K. Svoboda and S. M. Block, “Biological applications of optical from its infancy to an important interdisciplinary technique. forces”, Ann. Rev. Biophys. Biomol. Struct., 23 (1994) 247. The very small interaction of light with sample make this [11] F. Gittes, B. Schnurr, P. D. Olmsted et al., “Microscopic viscoelasticity: technique particularly useful for soft matter and biological shear moduli of soft materials determined from thermal fluctuations”, studies, where very weak forces, below 10−12 Nw, can be Phys. Rev. Lett., 79 (1997) 3286. [12] A. Meller, R. Bar-Ziv, T. Tlusty et al., “Localized dynamic light measured. Future development, already in progress, are in scattering: a new approach to dynamic measurements in optical the direction where OT will be combined with atomic force microscopy”, Biophys. J., 74 (1998) 1541. microscopy (AFM), visible spectroscopy and possibly with [13] D. Cojoc, F. Difato, E. Ferrari, R. B. Shahapure, J. Laishram, M. Righi, E. Di Fabrizio, V. Torre “Properties of the force exerted by filopodia other wavelength regime. In the next future, the availability and Lamellipodia and the involvement of cytoskeletal component”, of free electron laser source will open the possibility of PLosone, 10 (2007) e1072 on line www.plosone.org combining in vacuum manipulation, force measurement and [14] C. Bustamante, J. C. Macosko, G. J. Wuite, “Grabbing the cat by the fast chemi-physical phenomena in the temporal scale below tail: manipulating molecules one by one”, Nat. Rev. Mol. Cell. Biol., 1 −15 (2000) 130. 10 seconds. [15] T. T. Perkins, D. E. Smith, R. G. Larson and S. Chu, “Stretching of a single tethered Polymer in a uniform flow”, Science, 268 (1995) 83. The author would like to thank all collaborators and authors [16] K. Yoshikawa, “Controlling the higher-order structure of giant DNA that contributed to this paper through their work and the molecules”, Adv. Drug Deliv. Rev., 52(3) (2001) 235. [17] R. Borsali, H. Nguyen, R. Pecora, “Small-angle neutron scattering permission of using their additional material. and dynamic light scattering from a polyelectrolyte solution: DNA”, In memory of our beloved Prof. Franco Bassani who had Macromolecules, 31 (1998) 1548. invited me to write this contribution. [18] V. Garbin, D. Cojoc, E. Ferrari, M. L. J. Overvelde, S. M. van der Meer, N. de Jong, D. Lohse, M. Versluis, E. Di Fabrizio, “Changes in microbubble dynamics near a boundary revealed by combined References optical micromanipulation and high-speed imaging”, App. Phys. Lett., 90 (2007) 114103. [1] A. Ashkin,“Acceleration and trapping of particles by Radiation [19] D. Cojoc, E. Ferrari, V. Garbin, E. Di Fabrizio, H. Amenitsch, Pressure”, Phys. Rev. Lett., 24 (1970) 156. M. Rappolt, B. Sartori, P. Laggner, M. Burghammer, C. Riekel, [2] A. Ashkin, IEEE Journal on selected topics in quantum electronics, 6, ”Scanning x-ray microdiffraction of optically manipulated no. 6 (2000). liposomes”, Appl. Phy. Lett., 91 (2007) 234107. [3] A. Ashkin. “Forces of a single beam gradient laser trap on a dielectric [20] C. Liberale, P. Minzioni, F. Bragheri, F. De Angelis, E. Di Fabrizio, I. sphere in the ray optics regime”, Biophys. J., 61 (1992) 569. Cristiani, “Miniaturized all- fibre probe for three dimensional optical trapping and manipulation”, Nature Photonics; 1 (2007) 723.

Enzo Di Fabrizio Enzo Di Fabrizio is full professor of Physics at the University Magna Grecia in Catanzaro, where he teaches courses on general physics, nanotechnology and biophotonics. Moreover, he is director of the BIONEM (Bio and Nano Engineering for Medicine) Laboratory. The scientific activity at BIONEM Laboratory coordinated by Enzo Di Fabrizio spans from nanotechnology and biophotonic (including photonic crystal and plasmonic based devices) to biology. Special attention is dedicated to the in situ release of drugs for tumors care, through innovative devices based in general on nanocarriers such as nanocapsules, nanoparticles and polymers, and, in particular, on silicon nanoporous. Additional biophotonic devices are based on the SERS effect (surface-Enhanced Raman Scattering) or NEAR-INFRA (Near Field Infrared) are under development. These devices have a sensitivity close to that of single molecules. Further scientific effort is dedicated to the design and to the fabrication of microfluidic devices whose aim is the quantitative study of the conditions of interaction of drugs with endotelial tissues and to the diffusion, in the extracellular matrix. On these scientific themes, Enzo Di Fabrizio coordinates, and/or participates in different national and EU projects. During this last year, the laboratory has started an activity on low-consumption eco-compatible devices. At the TASC laboratory in Trieste, Enzo Di Fabrizio started LILIT laboratory (Laboratory for Interdisciplinary LIThography) of INFM (National Institute for Matter Physics - www.infm.it) and formerly, was responsible for the area of micro&nanotecnology at Elettra Synchrotron facility (www.elettra.trieste.it). His activity on micro and nanotechnology started more than 15 years ago and includes 5 years of research at University of Madison-Wisconsin, US. He has published more than 200 papers on international Journals. The international activity includes several collaborations with major western and eastern countries such as the US, Japan, China and India. BIONEM group at the year 2008 is composed by about 25 researchers, the value of the laboratory equipment is about 10 M€.

38 < il nuovo saggiatore percorsi

Max Planck - A conservative revolutionary

Manuel Cardona and Werner Marx Max Planck Institute for Solid State Research Stuttgart, Germany

1 Brief Biography

Max Planck has a deeply moving biography. He was not only one of the creators of modern Physics but also witness and actor of the most fateful events of the 20th century. Interwoven with these historic vicissitudes is his rather tragic personal life, having lost four of his five children, two of them through violence, the others, identical twins, in the aftermath of childbirth. His biographic literature is rather copious, starting with a scientific Celebrating the 150˚ Anniversary of autobiography [1]. We refer here to the other the father of Quantum Mechanics: biographical works we have used, in particular the theory that brought in a the investigations of the science historian Dieter conceptual revolution in the study Hoffmann [2-7]. We shall only mention some of the of Nature and a radical change in numerous short biographical accounts appeared in the description of its phenomena. scientific journals and the general press when appropriate. For the sake of conciseness, we give Planck’s biography in tabular form.

1858 Born April 23, 1858 in Kiel as the fourth child of the lawyer Johann Julius Wilhelm Planck and his wife Emma née Patzig. In his Lutheran baptismal record his name appears as Marx (sic) Karl Ernst Ludwig Planck. He published under the name of Max Planck but in the Web of Science he appears 12 times cited as MKE Planck. 1867 The family moves to Munich where his father had been appointed professor of law. Max attends the Maximilian gymnasium and soon distinguishes himself as one of the better students, in particular in religion and mathematics but also in languages. He makes friends with children of the upper bourgeoisie. His teachers attest him not only extraordinary intelligence but also impeccable behavior. He enjoys playing music, in particular the organ

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during religious services. 1874 At the age of 16, he obtains the high school degree that allows him to enter the university. During the winter term he attends the philosophy faculty of the University of Munich, undecided as to what further course to take. He enjoys listening to lectures in Mathematics, but decides to concentrate on Physics. He sings in the university choir, composes, acts at operetta performances and enjoys student life. 1876 He composes an operetta under the title (in translation) “Love in the Woods”. It is performed once at a fraternity. The score and text have been lost. 1877 Takes off in the spring for a hiking tour of Northern Italy with three classmates, visiting Venice, Florence, Genoa, Milan, Pavia, Brescia and the lakes. Travels by boat across the lakes and enjoys Bellagio, Villa Carlotta and Isola Madre; lengthy conversations with his travel mates about science, religion and their world picture, in which his conservative views often clashed with those of his friends, including Carl Runge who later became famous as a mathematician. 1877-1878 During the winter term he attends the Friedrich Wilhelms University of Berlin (which would later become his home as a teacher for almost 50 years). He listens to lectures by the famous physicists Helmholtz and Kirchhoff but is not particularly impressed by them: the first is too sloppy, the second too polished for his taste. In October 1878 he returns to Munich and takes an exam that qualifies him as a high school teacher. He substitutes for his former teacher in mathematics at the Maximilian Gymnasium. 1879 He obtains a doctoral degree with a dissertation on the second principle of thermodynamics. He regrets not to have had a real mentor in this important phase of his academic career. 1880 Only one year after his doctoral degree, he obtains his “habilitation” (certification of his ability to teach at a university) with a thesis about equilibrium states of isotropic bodies. At present such procedure in Germany takes three or more years. It confers the academic title of “Privatdozent”, making the holder a member of the faculty, without pay, till he receives a formal offer (Ruf) as a tenured associate professor (extraordinarius). Thus Planck continued to live with his parents. The first such “Ruf” came from a forestry academy which would not have enabled him to do creative research. He turned it down. While waiting for the “Ruf” he produced a few publications based on thermodynamics. They appeared in the Annalen der Physik, a journal which he helped to mold as editor from 1906 till 1928. 1885 He receives, from the University of Kiel, an offer of a position which was first meant for Heinrich Hertz. Hertz, however, turned it down and accepted an offer from the Technical University of Karlsruhe, which came together with large and well appointed experimental facilities. The Kiel offer then went to Max Planck, number two in the list. Planck spends some time writing an essay about “the essence of energy” in order to apply for an award offered by the Göttingen University. He finishes it in Kiel and is granted the second prize (the first was not given, apparently because of a controversy between Helmholz and Weber, a Göttingen professor, in which Planck had sided with the former). 1887 Having stabilized his personal situation, he marries, on March 31, his fiancée Marie Merck, daughter of a well known Munich banker and sister of a high school mate. Within a year, their first child, Karl, is born. Planck publishes in theAnnalen der Physik three papers on the ever increasing entropy which have received significant attention (48 citations as a whole, last cited in 1996). 1889 Planck receives a “Ruf” as “extraordinarius” and successor of Gustav Kirchhoff in Berlin. Again the offer had gone before to Heinrich Hertz who had become famous in Karlsruhe through his discovery of electromagnetic waves. Hertz, however, preferred a parallel offer from Bonn. Planck accepts the prestigious offer from Berlin. 1889 In April he takes up his new position in Berlin. Two daughters, Emma and Grete, identical twins, are born. 1890 He publishes two articles in the Annalen der Physik on thermal and electrical phenomena in electrolytes. They have become his two most-cited articles (279 and 266 times respectively,

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cited together 4 times in 2008 and 7 times in 2007, almost 120 years after publication). 1892 He is promoted to “ordinarius” in Berlin. 1893 Son Erwin, executed by the Nazis in January 1945, is born. 1895 Somewhat disenchanted by the poor impact of his earlier work, he takes up the hot topic of black-body radiation, an outstanding problem of thermodynamics, electromagnetic theory and industrial physics. 1900 In October 19 he announces his black-body radiation law as an empirical equation which accounts for the most precise extant measurements. In December 14 he presents, as an “act of desperation”, a theoretical derivation of that law using his hypothesis of energy quantization. Many historians feel that this work signals the birth of modern physics. 1905-1910 He comes out in support of Einstein’s special Theory of relativity. He writes several articles on the topic. One of them “the dynamics of bodies in motion” has been cited nearly 100 times, three times in 2008. 1909 He lectures at Columbia University in New York City. His wife of 22 years, Marie, dies of a lung ailment, leaving him with four adolescent children. 1911 On March 14 he marries 24 years younger Marga von Hoesslin, Marie’s niece. In December their son Hermann is born. Nothing much is known about Hermann. He participated in the German campaign against Russia as an enlisted man, returned as an “Obergefreiter” (pfc) and died of polio in 1954. In October 1911 Planck attends the first Solvay conference, dealing with the theory of radiation and quanta. 1912 He is appointed permanent secretary (equivalent to president) of the Prussian Academy of Sciences, a position he held till his resignation in 1938 (at the age of 80). 1913 Planck is elected rector of the University of Berlin and is instrumental in bringing Einstein to positions in the Academy, the newly founded Kaiser Wilhelm Institute (KWI) of Physics and the Berlin University. 1914 Einstein arrives at Berlin in April. The first world war starts on August 1. Planck’s sons Karl and Erwin enroll in the Army. Planck, together with 93 well known German intellectuals, signs the notorious manifesto to the “Kulturwelt” blaming the Belgians for all sorts of atrocities, justifying the violation of Belgian neutrality and proclaiming the unity of German militarism and culture. Planck later realized its devastating effect on international scientific relations. In June 1915, when the going was rough, he signed a statement by 1347 intellectuals trying to explain the manifesto and in 1916 wrote a letter stating that, in spite of the war, international scientific relations were by all means to be preserved. Most of Einstein’s colleagues, including Jewish ones, had signed the infamous “Kulturwelt” document but Einstein did not. Together with a close friend he wrote a counter-appeal saying that the document was “unworthy of what until now the whole world has understood by culture”. He hardly found any cosigners but the document was finally published in Switzerland (Einstein had a Swiss passport). Planck’s sons Karl and Erwin became army officers, to the pleasure of Max who expected from them great heroic deeds. Erwin is severely wounded in the battle of the Marne and taken prisoner of war. 1916 Son Karl is killed in action in Verdun on May 26. Max expresses, in a rather Wagnerian way, sorrow and pride concerning Karl’s heroic death in the service of the fatherland, the emperor and God. Karl never got along well with his father who finds solace in the fact that the Army had made a useful man out of him. 1917 Max’s daughter Grete dies of childbirth on May 15, a baby daughter survives. Under the auspices of the Red Cross Erwin is interned in Switzerland. On October 1 Max becomes a member of the board of directors of the recently founded Kaiser Wilhelm Institute of Physics. 1918 The war ends with Germany’s defeat, the Kaiser’s abdication and the proclamation of the republic, all facts that compound Max’s personal tragedies. His “Weltbild” collapses but he is able to find solace in helping rebuild German science. Max had been considered for the Nobel Prize in Physics since 1907 and regularly till 1919, the year in which he was belatedly given the prize which had not been awarded in 1918. He had been nominated a total of 75 times.

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1919 Daughter Emma, after marrying her widowed brother in law, dies in November 21 in the process of childbirth. A daughter also survives. Max is belatedly granted the 1918 Nobel Prize “in recognition of the services he rendered to the advancement of physics by the discovery of the energy quanta”. He joins the Deutsche Volkspartei, a liberal (in economic matters) nationalistic party, the right wing of the Nationalliberale Partei founded by Gustav Stresemann (co-winner of the 1926 Nobel Peace Prize and Chancellor during the Weimar Republic). 1920 In the Midsummer of 1920 (sic) he officially receives the 1918 Nobel Prize in Stockholm, together with his colleague Fritz Haber (Chemistry, also 1918) and the ultranationalist Johannes Stark (Physics, 1919) who was later to become a rabid anti-Semitic Nazi. He continues publishing about two low profile articles a year, not surprising in view of his increasing public service commitments and the fact that he always worked alone: he left no school. His personal tragedies and tragic political events must also have made a dent. 1926 Max is elected a member of the ancient (founded in 1652) Academie der Naturforscher Leopoldina. In 2008 the Leopoldina became the German Academy of Sciences. 1927 He becomes emeritus at the Berlin University on October 1 and is succeeded by Erwin Schrödinger. 1929 Planck and Einstein become the first awardees of the Max Planck Medal of the German Physical Society, created to commemorate the 50th anniversary of his doctorate. 1930 He becomes President of the Kaiser Wilhelm Gesellschaft (KWG) till July 25, 1938 and, with his other public service appointments, the most influential person in German science. 1933 Without a majority of his Nazi party (NSDAP) in parliament Adolf Hitler is appointed Reichskanzler (Prime Minister) on January 30. On February 27 the Reichstag burns. On February 28 the parliament approves a decree suspending basic rights. Murders of presumed enemies of the NSDAP start. On March 6, new elections in which the NSDAP gets 44% of the votes, not enough to form a government. On March 24 the parliament approves the Ermächtigungsgesetz (with the votes of all parties except communists and socialists) enabling Hitler to rule by decree. The atrocities increase. Planck’s point of view is that it is a transient situation needed to restore order, after a while the situation will settle down like in the case of natural catastrophes. On April 7 the “law for the restoration of the professional civil service” is approved by decree. According to it, university professors would become civil servants but ethnic Jews (religion played little or no role) were excluded from the civil service (with few exceptions, later struck down). Mass expulsions of non-Aryan professors and other prominent dissidents start. Max Planck was, at the time, vacationing in Italy. Some colleagues asked him to return immediately to Berlin but he followed the advice of his secretary at the KWG and continued his vacation. Later he mentioned that he was happy to see that the new law was put into effect without any incidents. The law was, by the way, similar to the disposition in the Italian racial laws of 1938, which also barred students with the wrong ethnicity from attending public schools and universities. Before Planck left for vacation, Einstein, at the time in the United States, announced that he would not return to Germany where there was no longer “civil liberty, tolerance, and equality of the citizens before the law”. He sent in his resignation from the Prussian Academy. Planck, always willing to compromise, wrote to him “By your efforts your racial and religious brethren will not get relief from their situation, which is already difficult enough, but they will be pressed even more”. He added that the value of an act lies not in its motives but in its consequences. The mass exodus started, the KWG being in a somewhat better shape than universities because of having positions paid by industry and being able to keep Jews of non-German citizenship (e.g., Lise Meitner). By and large no protest from Aryan colleagues was heard. On May 17 Planck was granted an audience with Hitler to discuss this and, as we now know, other matters. At the end of a long and apparently satisfactory conversation on the future of science and the KWG, he asked Hitler not to dismiss highly competent non-Aryan scientists. He mentioned that there were two kinds of Jews, those beneficial and those pernicious to the

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German society and that one should differentiate. Hitler went into one of his rages and said that the Jews themselves should do that and that for him Jews were all the same… Planck stood up and took leave. This story, carefully manicured, has been mentioned in Germany for years as one of the few proofs of the existence of an opposition and of Max Planck’s integrity. Nowadays we know that matters were not as simple. 1935 A memorial service was organized in Berlin a year after the death of Fritz Haber. Haber, a Jewish (ethnic but baptized) Nobel laureate, who had invented the ammonia synthesis, was not dismissed as a director of his KWI on the formal grounds of his merits in the first world war. He, however, would have to implement the dismissal of Jewish colleagues, which he refused to do. Instead he chose emigration. Attendance of state employees to Haber’s memorial service was forbidden by the minister of education who, however, left open the possibility of asking for a special dispensation. Planck and also Otto Hahn, in what has been portrayed as an act of defiance, attended the service without any subsequent sanctions. The fact that many foreign dignitaries were present, among them representatives of the Rockefeller Foundation, which was negotiating the funding of a new building for the KWI of Physics, reduces the impact of the act of defiance which Planck’s attendance to Haber’s memorial service has been told to represent. 1937 At the age of 79, Planck leaves the presidency of the KWG. He is succeeded by Carl Bosch (Nobel Laureate for Chemistry, 1931) till the latter’s death in 1940. Bosch often confronted the NSDAP hacks, sometimes inebriated. His successor from 1941 was Albert Vögler, an executive of a large steel conglomerate. While not a member of the NSDAP he certainly was a sympathizer and financial supporter, having been elected to parliament in 1933 on an NSDAP ticket. While not fully compliant to the Nazi hierarchy, he heavily compromised. He poisoned himself while being arrested at his home in 1945. We have found no scientific works of Vögler, who succeeded two Nobel laureates as KWG President and was succeeded by two more. 1938 On the occasion of Planck’s 80th birthday Louis de Broglie is awarded the Max Planck Medal. The KWI for Physics, funded by the Rockefeller Foundation, is inaugurated under the directorship of Peter Debye, a Dutch Physical-Chemist who even as an Aryan, was forced to emigrate in 1940. Debye had proposed to name his Institute after Max Planck but Nazi members opposed him. So, it remained the Kaiser Wilhelm Institute of Physics. Lise Meitner, a co-discoverer of nuclear fission and a close friend of the Plancks, had to leave Germany in a cloak-and-dagger operation: she was an Austrian ethnic Jew (nevertheless baptized) who lost her foreign passport as a result of the Anschluss. 1943 The Plancks leave their endangered home in Berlin and move to a friend’s house in Rogätz (Elbe). 1944 Their abandoned home in Berlin-Grunewald is bombed out. Planck’s library is destroyed. 1945 Planck’s son Erwin is executed as having been involved in the plot to assassinate the dictator. He had accepted a position in a future cabinet and had participated in drafting a new constitution. Planck and various associates and friends wrote letters to the highest officials asking for clemency, to no avail. Erwin, Max’s closest son and friend, was executed on January 23. After straggling with Marga through the woods around Rogätz in the search of food, they are captured by an American commando and taken to Göttingen, thus avoiding being captured by the advancing Russians. The English authorities decide to reconstruct the KWG . Planck (age 87!) is asked to take over, temporarily, its presidency. Once more, he follows the call of duty. 1946 He is invited (and accepts) to attend the Newton celebrations of the Royal Society in London. It hurt him that he was introduced as a guest, “representing no country” (Germany had ceased to exist). Otto Hahn takes over the presidency of the newly reestablished KWG whose name is changed to Max Planck Gesellschaft while Max Planck is still alive. Planck becomes its honorary president. In June he gives his last lecture in Göttingen. 1947 In August he fell and had to be hospitalized. He died in October 1947 and is buried in Göttingen.

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2 Scientific Work was a careful recapitulation and exegesis of the works of Rudolf Clausius (1822-1888), who had introduced the concept Theoretical physics at the end of the 19th century of entropy and the second law of thermodynamics. Planck In the second half of the 19th century, when Planck started his removed some ambiguities and contradictions and extended academic career, physics was widely seen as an experimental the concept of entropy to irreversible processes and a endeavor – in spite of the early works of Galilei (1564-1642) measure of irreversibility. In his scientific autobiography [1] and Newton (1643-1727), the first theoretical physicists in Planck discussed the poor impact of his dissertation: “None of the modern sense. Theory was confined to mathematics as my professors at the university had any understanding for its an ancillary science, e.g., providing interpolation formulae contents. I found no interest, let alone approval, even among and error statistics for experiments. Experimental physics had the very physicists who were closely connected with the become the key science within the physics institutes at the topic.” Here we also find the famous statement that “A new German universities [4]. The directors were full professors, scientific truth does not triumph by convincing its opponents leading well equipped “empires”, the paternalistic structure and making them see the light, but rather because its of the times giving them the status of monarchs. Associate opponents die and a new generation grows up that is familiar professors who wanted to avoid conflicts, and eventually with it.” Irony of history: He did not immediately see the be promoted, became active in research fields where less consequences of his most important discovery. equipment was needed, in particular in theoretical physics. At the start of his career as a researcher (1879) Planck became Moreover, the more profitable main lectures were given fascinated by the subject of entropy. He was confronted with by the full professors, whereas special lectures like those the statistical interpretation of Ludwig Boltzmann who had in theoretical physics were held by associate professors postulated the relationship between microscopic parameters (receiving much lower tuition fees (Hörergelder) because and the macroscopic properties of matter. At that time, of the smaller number of students). At the end of the 19th Planck rejected the statistical approach, because, he felt, it century, there were only two universities with chairs in would contradict the absolute universal validity of the laws theoretical physics: the Friedrich Wilhelms University in of nature which he strongly believed in. For him, probability Berlin (Gustav Kirchhoff, 1824-1887), and the University of would imply exceptions from that invariable validity. He Göttingen (Woldemar Voigt, 1850-1919). At the beginning therefore preferred the macroscopic phenomenological of the 20th century the situation rapidly changed. The approach of Clausius and Wilhelm Ostwald (1853-1932) and development of mathematical physics in the first half of the consequently refused the atomistic view of matter. We should 19th century (Euler, Fourier, Poisson) had already shown the mention here that the famous formula combining entropy

potential of the new discipline. Heinrich Hertz (1857-1894), with probability (S = kB ln W) has not been introduced by Hermann von Helmholtz (1821-1894), and Ludwig Boltzmann Boltzmann but by Planck, who named kB the Boltzmann (1844-1906) represent pioneers with a double role in constant. As we shall see later, he even reported the earliest

experimental and theoretical physics. But it was in particular and rather precise determinations of kB. However, Planck’s Max Planck and Albert Einstein (1879-1955), who caused a skepticism about the probability concept and his opposition breakthrough concerning acceptance and recognition. A to atomism did not wane until he realized its potential for chair in theoretical physics became no longer a necessary evil a convincing theoretical explanation of the black-body but an important necessity. radiation.

Thermodynamics Black-body radiation Beside the time-honored mechanics, electrodynamics (which After Hermann von Helmholtz had introduced the by then included optics) and thermodynamics were the concept of free energy, Planck applied it to chemical central basis of physics at the end of the 19th century. There thermodynamics, in particular to the equilibrium of gas were speculations about nothing less than the unification reactions, a very important discipline for the expanding of these three fields of physics. The discussion about the chemical industry. Planck soon became one of the leading hypothetical ether implied the possible unification of experts in thermodynamics. However, the American physicist mechanics and electrodynamics, while the relationship Josiah Willard Gibbs (1839-1903) had already developed between mechanics and thermodynamics was clarified on a similar “theory of chemical equilibrium”. His work was the basis of statistical physics and the hypothesis that all published in 1876, but was overlooked in Europe and not matter is composed of atoms. Planck’s dissertation at the translated until 1892. The situation differed from that in University of Munich, where he had studied physics between the present day, the US not having yet become the top 1874 and 1879 (with an intermission of two semesters in nation in science. Although not fully equivalent to his own Berlin), dealt with the second law of thermodynamics and contributions, Planck recognized the priority of Gibbs’s work.

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Maybe somewhat frustrated about his lack of a scientific complete texts can be found in ref. [8], Vol. I, pp. 493-600. breakthrough, Planck turned to the theory of heat radiation. In this endeavor, he now found it convenient to accept The rapid development of the lighting industry in the last Boltzmann’s atomistic point of view and thus relate entropy decades of the 19th century, and the competition between to disorder in the case of a large set of massive particles (see electric and gas light, required precise experiments ref. [8], Vol. I, pp. 493-504). In order to reach thermodynamic and better standards for the luminosity of light sources. equilibrium (a maximum of S) these particles must interact, Moreover, an understanding of the processes involved in either through collisions with each other or with the light absorption and emission was needed. For such reasons, container walls. Planck tries next to find parallel concepts the German industry (in particular Werner von Siemens) and for em waves (their corpuscular aspect had to wait till the German government established the German bureau of Einstein’s 1905 Nobel winning work). He then introduces the standards, named Physikalisch-Technische Reichsanstalt (PTR, concept of natural radiation (incoherent partial waves) as now PTB), with Hermann von Helmholtz as its first director. opposed to coherent monochromatic waves. Around a given Its charge was to perform the most accurate measurements wave number ν one has an infinite number of em waves, of fundamental constants and to push research on unsolved depending on their propagation direction, polarization, basic problems in physics. phase, and exact value of ν. Hence, one can compare a set of The concept of the black-body radiation had been introduced massive particles to a natural set of em waves of frequency in 1859 by Kirchhoff who defined a black-body as an object ν. One must, however, introduce some kind of mechanism to that absorbs all thermal radiation falling on it. When it is have the em waves interact with each other so as to be able cold, no radiation is reflected or transmitted and the object to establish equilibrium. appears black. When it is hot, it becomes an ideal source Planck does that by introducing in a black-body cavity one of thermal (and also optical) radiation. Several physicists or more small fictitious dipole oscillators which absorb investigated the spectral distribution of the black-body and reradiate (with an arbitrary direction, polarization, and radiation. An important contribution was the discovery of frequency if ν covers a small but finite interval). He first the Stefan-Boltzmann law, which states that the total energy treats concentric waves with one dipole at the center of radiated per unit surface area of a black-body in unit time is the cavity. The total energy of the waves and the oscillating directly proportional to the fourth power of the black-body’s dipole can be easily calculated. At that point he proceeds to temperature (I ~T 4). The next important step was a discovery postulate (he calls it “to define”) two functions (one for the of Wilhelm Wien (1864-1928) in the year 1893, the so-called oscillator, the other for the waves) whose sum, he checks, displacement law, i.e., the inverse proportionality between invariably increases with time, till a maximum is reached at the wavelength of the peak in the spectral distribution of the thermodynamic equilibrium. He thus calls these functions black-body emission and its temperature. Three years later entropy. They enable him to define a temperatureT for (1896) Wien presented a semi-empirical radiation law (Wien’s the em waves in equilibrium inside the cavity. From the energy distribution law) that described well the experimental equilibrium state that maximizes the entropy for a given T he data available at the time. retrieves Wien’s law for the radiation intensity Kν per unit area, unit solid angle and frequency interval dν: Enters Max Planck In 1887 it was generally accepted that thermal and optical , radiation were related to electromagnetic waves, as described by Maxwell’s equations. The latter, however, were where the two constants a and b are, in present day’s time reversal invariant and, as such, alien to the concept of notation: b = h (Planck’s constant, which of course he did not irreversibility as embodied by the thermodynamic concept call so) and a = h/kB. kBwas first called Boltzmann’s constant of entropy. Planck realized that in order to describe black- by Planck. From an analysis with the above equation of body radiation with Maxwell’s equations it was necessary to experiments by Lummer, Paschen, Pringsheim, and Wanner, × –27 × × –16 extend the concept of entropy S to such waves (an inverse Planck derives h = 6.885 10 erg s and kB = 1.43 10 temperature would then be obtained as the derivative erg /°C, rather close to presently accepted values (the values of entropy with respect to added thermal energy). He he obtained later using his full radiation law are even closer thus embarked in a program to rigorously introduce to the accepted ones). thermodynamics into electrodynamics and electromagnetic In a seminar, given on October 19, 1900 at the German (em) wave propagation. His initial work was presented in Physical Society (DPG), Ferdinand Kurlbaum reported great detail and an almost axiomatic way in five lectures significant deviations from Wien’s law, in particular at small he gave at the regular sessions of the Prussian Academy frequencies, of his black-body measurements at the PTR of Sciences, three in 1897 and two in 1898 and 1899. The together with Heinrich Rubens. In the same session (he had

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received the measured data from Rubens before) Planck bears his name under the assumption that ε is proportional to suggested an empirical modification of Wien’s law, based on ν, the proportionality constant being h [13]. Also labeling the the replacement of e– (aν/T) by [e (aν/T) – 1]–1. At high values of ν whole procedure an “act of desperation” he derived the now the modified expression coincides with the original one, but famous law discrepancies appear at low values which better represented . the experimental data reported in the same session of the DPG. This fact led Planck to start a search for a theoretical explanation of the new (Planck’s) radiation law which he Initially, Planck saw his constant as a mathematical reported at a meeting of the DPG held on December 14, 1900. artifice, from which he hoped to get rid of later or which This date is considered by many as the beginning of modern could be included somehow into classical physics. physics. Both lectures were published in the proceedings of Figure 1 demonstrates convincingly the longevity of the DPG [9-10] (see also ref. [8], Vol. 1, pp. 687-689, pp. 698- Planck’s equation, showing a rather impressive fit of recent 706). A summary of these articles appeared in the following experimental data for the cosmic background microwave year 1901 in the Annalen der Physik [11] (see also ref. [8], Vol. 1, radiation resulting from the big bang, corresponding to T = pp. 717-727). 2.735 K [14]. The decisive step in this work was the assumption that within It has often been stated that Planck became a revolutionary a cavity there is a large number N of equal oscillating dipoles against his will. Indeed, between 1901 and 1906 he did not in equilibrium with the em radiation. He had earlier derived publish anything on black-body radiation and quantization the relation between the energy of the em field as a function [7]. In the year 1910 he still instructed to “proceed as of that of the oscillators. He further assumes that the energy conservatively as possible in introducing the quantum of each oscillator is not continuous but actually an integer of action h into the theory, i.e., only those modifications multiple of a small (quantum of) energy ε. He called these should be made to the existing theory as have proven to be oscillators “energy cells” and treated them with Boltzmann’s absolutely necessary” [15]. Planck’s presentation of Einstein statistical methods. This was referred to by Planck as an “act of on the occasion of his election as member of the Prussian desperation” in a letter of 1931 to R. W. Wood [12]. Academy of Sciences in 1913 again reveals his conservative In his lecture at the DPG meeting on December 14, 1900 he attitude when he stated that Einstein “in his speculations may regarded energy “as made up of a completely determinate sometimes have gone a bit too far, e.g., with his hypothesis number of finite equal parts, and for this purpose I use the of the light quanta, but it is difficult to hold this against him”. constant of nature h” [9]. He is then able to derive the law that Not surprisingly, in 1908, when Planck became a candidate

FIG 1: Fit of the measured cosmic background microwave radiation with Planck’s equation for T = 2.735 K [14] (reproduced by permission of the AAS). The first author, J.C. Mather, shared with his colleague G.F. Smoot the 2006 Nobel prize for physics.

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for the Nobel prize, the prize committee decided to wait for a quantization but, like Planck, he had difficulties going a step final clarification of the relevance of quantization – until 1920 further and agreeing with the probabilistic interpretation of when Planck received the long overdue prize (retroactively quantum theory. Planck approved many of the advancements for the year 1918). He has been nominated more often than resulting from the developments in quantum mechanics but any other previous candidate (75 times). did not play a significant role in them. According to Max von Laue and many science historians, the events that took place at the December 1900 meeting of Planck as one of the first managers of modern science the DPG signal the birth of quantum physics. However, none As mentioned in the biography, his appointments at the of Planck’s publications contains any statement about the Berlin University, at the Prussian Academy and the KWG physical meaning of his constant, indicating that his concept converted Planck, in spite of his rather modest personality, has to be clearly distinguished from what we nowadays into the most important representative of German physics. understand as quantization [7]. The philosopher of science Several other important appointments followed, which Thomas S. Kuhn discussed this in detail and concluded probably catapulted him into the most powerful person in all that Planck does not deserve the credit [16]. Einstein’s of German science. We mention here the presidency (1921- publication on the hypothesis of light quanta in 1905 was 1922) of the Deutsche Gesellschaft für Naturforscher und Ärzte definitely the first clear statement of energy discontinuity or (German Society of Researchers and Physicians) and charter quantization. Before 1905 Planck’s findings were discussed membership of the executive board of the Notgemeischaft only internally by PTR physicists. However, as the history of der Deutschen Wissenschaft (Emergency Association of many other discoveries reveals, the role of the participants German Science) from its foundation in 1920 till 1932. is mostly rather complex and the demand for one “hero” and The name was changed in 1929 into the present Deutsche a particular date is not realistic. Nevertheless, Planck’s use Forschungsgemeinschaft (DFG). of the elementary quantum of action was the first step in This organization had been created by Planck, von Laue and introducing quantization into physics. others to raise funds to relieve their lack in German science resulting from the war and the subsequent depression. While Planck and Einstein a civil servant, Schmidt-Ott, ex Prussian minister of Culture, A fascinating aspect in Planck’s biography is his relation was placed at its top, Planck became the ranking scientific to Albert Einstein, both on the scientific and the personal officer and was deeply involved in engaging institutions level. Planck was deeply impressed by the revision of the (universities, academies and other scientific societies, state Newtonian concept of time in Einstein’s Special Theory of governments, the Rockefeller Foundation, national and Relativity. He quickly accepted its basic tenets and put it on foreign industrial organizations, such as Siemens and General the agenda for lectures and discussions in Berlin – and as a Electric) and individuals (such as the Japanese industrialist thesis topic for many of his PhD students. Although reluctant Hajime Hoshi). A feather in the cap of this organization is the with regards to Einstein’s quantum hypothesis of light, he grant given in 1925 to the theorists who developed quantum finally became the most important patron of the young mechanics (Heisenberg, Born), a fact which was criticized Einstein. Planck played a key role when Einstein moved by more conventional physicists who were not receiving to Berlin and became one of the rare full-time members support. Planck defended this policy with the statement (with pay) of the Prussian Academy of Sciences, professor “Quantum mechanics is at the center of interest of the without teaching duties at the University and director of a physicists of all countries…”. newly created Kaiser Wilhelm Institute of Physics. Although Planck was appointed Senator of the KWG in 1916, becoming the staunch conservative attitude of Planck, both with its president from 1930 till 1937, thus having to steer one of respect to science and politics, and the unconventional and the largest science funding organizations world wide through antiauthoritarian Einstein were not compatible, their personal the rather stormy waters of Nazi rule. As already mentioned relation was coined by mutual respect and admiration. in his biography, here he misjudged at the beginning the real However, Planck’s unrealistic, illusory and compromising nature of the Nazi philosophy and rulers, giving himself to attitude during the first years of the Nazi-power became a the illusion that it was only a temporary evil which may even severe strain for their relation [17]. They finally broke contact help to restore, at least in part, his conservative society. In his after Einstein’s emigration and Planck’s criticism of it (see tenure of office at the KWI (1930 till 1937), covering the pre- biography above). Thereafter, Einstein only wrote a letter of war Nazi period, he, of course, had to contemporize. condolence to Planck’s wife on the occasion of his death, Some of his reproachable actions were in principle harmless: praising their friendship and the happy times they had spent “Heil Hitler” in letters, addressing Hitler as “Mein Führer”, Nazi together in Berlin. Compared to Planck, it is now admitted salute (always raising the hand rather shyly), others were not that Einstein established the definitive concept of energy as trivial: dismissing non-aryan colleagues (although he tried

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to rescue some with limited success), participating in the old papers may now be so well known that they appear in organization and governance of some from our point of view textbooks rather than being cited. The question arises as rather objectionable institutes (such as the infamous KWI for to whether the impact of early pioneers of science like Max Anthropology, Human Genetics and Eugenics, directed as of Planck can be quantified by bibliometric methods usually 1940 by Freiherr von Verschuur who was connected with the applied to present day scientists. Carefully establishing and infamous Dr. Mengele, an ex graduate student of Verschuur). interpreting the citations of Planck as a case study seems to At some point Planck held a meeting with Nazi authorities be a reasonable way to proceed. in which the decision was made of teaching the theory of relativity and mentioning his author, but adding that even Methodology without Einstein someone else would have come up with the The data presented here are based on Planck’s collected theory. Planck paid dearly for his misjudgment of the Nazi works analyzed using the Thomson Reuters citation indexes evil. As discussed in the biography, his dear son Erwin was under the Web of Science (WoS), especially the Science sentenced by the Volksgericht (Peoples Court) and executed Citation Index (SCI). The WoS is accessible under the Web of in January 1945. Knowledge (WoK), the search platform provided by Thomson Planck, while fulfilling his managerial duties, never forgot to Reuters (the former Thomson Scientific, emerged from the keep contact with science, even doing scientific work himself. Institute for Scientific Information, ISI) [19]. In addition, the He had (from 1892 till 1925) 25 graduate students and seven INSPEC database for Physics, Electronics, and Computing and degree holders who obtained the “habilitation”. Planck never SCIsearch (SCI accessible under the database provider STN coauthored any articles with them, although in one particular International) have been consulted for the present study [20]. case of a graduate student (Kurd von Mosengeil), who had The WoS stretches back to 1900 in its General Search mode, had a serious accident, Planck worked on his thesis to make the SCI under STN International only goes back to 1974. it acceptable for publication in the Annalen der Physik. It is The WoS offers two search modes. TheGeneral Search thus difficult to say that, like in the case of Max Born [18], he mode gives access to the articles (no books, no conference left a school, although two of his charges were awarded the proceedings unless they appear in source journals) published Nobel Prize (Max von Laue and Walther Bothe) and additional since 1900 and covered by the so-called WoS source journals: two should have been awarded it (Walther Meissner, for the about 9000 journals currently selected by the staff of Meissner-Ochsenfeld effect; Walter Schottky, for pioneering Thomson Reuters as contributing significantly to the progress work in semiconductors). He boasted, while active in of science. The Cited Reference Search mode gives access to Berlin, of attending regularly the seminars of the Prussian all references appeared in source journal articles (cited either academy and the Berlin Physical Society (later renamed as correctly or containing errors). The cited references are not German after Planck’s suggestion), having attended more limited to articles published in source journals but include any meetings than any of his colleagues. Few present day science other published material (e.g., the Bible or the Koran). In other organizers follow his example. He regularly spoke at the words: The citing papers are limited to source journal articles meetings of those learned societies, the proceedings of his published since 1900, but the papers cited therein are not talks, some highly cited, are available in his collected works limited concerning document type or publication year. [8]: 34 articles correspond to presentations at the Prussian academy and 17 to presentations at the Physical Society Planck’s most-cited papers meetings. The WoS General Search for “Planck M” as author name revealed 111 articles for the period 01-01-1900 till the date of search (01-06-2008). However, this number is misleading 3 Bibliometric analysis in two aspects: 1) Planck’s pre-1900 articles are not fully covered by the WoS, and 2) at least 21 out of the 24 articles One way to estimate the impact of a researcher is to count past 1950 were published by a namesake, an oncologist. the number of times that his papers have been included Hence, there are a total of 90 articles accessible as source in the reference lists of other papers. The number of records under the WoS. An additional search in the Physics citations is often taken as a measure of the attention an Abstracts database (INSPEC) in the time period 1898 till 1950 article, a researcher or an institute has attracted. Although revealed 74 articles, including 3 pre-1900 papers. According citation numbers reflect strengths and shortcomings and to a recent count, there are at least 18 articles published in are therefore frequently used for research evaluation, the the Annalen der Physik prior to 1900 [21]. This journal, which number of citations cannot easily be equated with the he edited between 1907 and 1928, was his preferred choice overall significance: 1) The final importance of the more for publishing his work, starting 1881 and ending 1941. A recent papers may not yet be clear, and 2) the results of citation analysis based on the WoS Cited Reference Search

48 < il nuovo saggiatore m. cardona and W. Marx: max Planck - A conservative revolutionary

Author(s) Journal Title Citations

Annalen der Physik 39/275, 161- Excitation of electricity and M. Planck 279 186 (1890) heat in electrolytes

The potential difference between two dilute Annalen der Physik 40/276, 561- M. Planck solutions of binary 266 576 (1890) electrolytes

The energy distribution law Annalen der Physik 4/309, 553- M. Planck of the normal spectrum 198 563 (1901) On the theory of the Verhandlungen der Deutschen energy distribution law of M. Planck Physikalischen Gesellschaft 184 the normal spectrum 202/237 (1900)* An essay on statistical Sitzungsberichte der Preußischen dynamics and its M. Planck Akademie der Wissenschaften generalization to quantum 117 324-341 (1917)** theory

The dynamics of moving Annalen der Physik 26/331, 1-34 M. Planck systems 95 (1908) Annalen der Physik 1/306, 69-122 On irreversible radiation M. Planck 91 (1900) processes * Both articles are not included as WoS source records ** This paper contains Planck’s contribution to the Fokker-Planck equation.

Tab I. The most-cited articles by Max Planck. Source: Thomson Reuters Web of Science (WoS), date of search: 01-06-2008. mode (i.e. including the pre-1900 papers) reveals Planck’s those about black-body radiation and energy quantization most-cited papers as given in tab. I. The citations of the published in1900 [9-10] and summarized in 1901 [11], but pre-1900 papers within the time period from the year of this is not the case. However, if we add up the citations of publication till 1900 are currently not available under the these three articles, we obtain almost 400 citations. If we WoS. The coverage of the pre-1950 physics literature by the include the preceding five communications on irreversible WoS seems to be sufficiently complete to justify the analysis. radiation processes published between 1897 and 1899 in Misspelled citations (incorrect with regard to the numerical Sitzungsberichte der Preußischen Akademie der Wissenschaften data: volume, starting page, and publication year) are a (see ref. [8], Vol. 1, pp. 493-600) we find altogether 450 general problem in citation analysis. The references of early citations. This situation is rather similar to that encountered articles are particularly susceptible concerning “mutations”. in the case of Einstein: His most-cited articles are not those Between 1881 and 1941 Planck published altogether 45 dealing with the special and general theory of relativity, but papers in the Annalen der Physik [5]. This still prestigious the paper dealing with the so-called EPR paradox [22] (3364 journal (before WW II comparable to Physical Review at citations) followed by an article in which the molecular radius present) is cited with an above average error rate, due to the and Avogadro’s number are determined using viscosity data changes in the journal name, editors, location of editorial [23] (1924 citations plus 1166 citations for an erratum [24]). office and the various series. We included here the misspelled Obviously, important early articles may not have been cited citations by hand (provided that we were able to identify according to their importance. Sometimes they are even them and assign them to a specific Planck paper). rarely cited, as compared to much less fundamental works One may have surmised that Planck’s most-cited articles are (see below).

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Citation History of the most-cited Planck Articles 30

Ann Phys V39 P161 (1890) 25 Ann Phys V40 P561 (1890) Quantum of Action - total s

on 20 ti ta Ci

f 15 o er

mb 10 Nu

0 00 10 20 30 40 50 60 70 80 90 00 10 19 19 19 19 19 19 19 19 19 19 20 20 Publication Year of Citing Articles

Fig. 2 Time-dependent number of citations (citation history) of the three most-cited articles by Max Planck. The red curve comprises the total impact of the three papers on rank 3 and 4 in tab. 1, i.e., refs. [9-11]. Misspelled citations (incorrect with regard to the numerical data: volume, starting page, and publication year) are included here if we were able to identify them.

The graph displaying the time-dependent evolution of a Note that the impact peak of the quantization papers around single article is sometimes called its citation history. Each 2005 coincides with the centennial of Einstein’s annus article develops its own life span as it is being cited. With mirabilis. Figure 3 shows the number of citations per year time, the citations per year (citation rate) normally evolve within the first three decades. The citations of the famous following a similar pattern: They generally do not increase 1905 paper by Albert Einstein [25] on the light-quantum substantially until one year after publication. They reach a hypothesis (522 citations), introducing the photon in the summit after about three years, the peak position depending discussion of the photoelectric effect and responsible for his somewhat on the research discipline. Subsequently, as the Nobel Prize, are shown for comparison. articles are displaced by newer ones and interest in the field The citations of Planck’s quantization papers soon waned, wanes, their impact decreases, leading to the accumulation of with only 9 citing papers between 1910 and 1930. A further citations at a lower rate. Finally, most papers are barely cited analysis reveals that the majority of the citations appear in or forgotten. Figure 2 shows the citation history of the three papers published by PTR physicists working at that time most-cited Planck papers given in tab. 1. on the spectral characteristics of the black-body radiation In contrast to the standard “canonical” time pattern (i.e. Paschen, Lummer, Pringsheim, Kurlbaum, Rubens) and mentioned above, the citations of the most-cited Planck also by Planck himself. By and large, at the beginning of the papers are highly delayed (such papers have been called 20th century Planck’s introduction of the concept of energy “sleeping beauties”). We have analyzed the recent citations of quantization was not widely mentioned in the physics Planck’s two most cited papers (published in 1890 and having literature. Even Planck himself did not further discuss the to do with electrolytes). We find a total of 10 for the years physical significance of his constant. Today, in particular 2005-2008. The citing papers cover a vast range of subjects, Einstein’s paper on the light quantum hypothesis is seen as including Darwinian dynamics, in vivo skin electroporation, the beginning of our present understanding of quantum electrodiffusion, fuel cells, cation exchange, electrochemistry theory, absorbing and incorporating Planck’s approach. of metallurgical processes, transport through membranes, Except for Max Born, none of the founders of quantum and soldered interconnections. mechanics, like Werner Heisenberg or Erwin Schrödinger, The citations of the three Planck articles introducing his cited the quantization papers by Planck or the photoelectric famous constant are shown in fig. 2 as a whole. Interestingly, effect paper by Einstein. Within the time period 1900 till their impact is almost negligible during the time of the 1925 there are only 2 citations by articles published in the development of quantum mechanics (around 1925/1926). Physical Review. The citing papers of Planck’s quantization

50 < il nuovo saggiatore m. cardona and W. Marx: max Planck - A conservative revolutionary

Quantization Articles: Planck vs Einstein 10

9 Planck 1900

8 Planck 1901

7 Planck Total

Number of Citations of Number 3

0 1900 1902 1904 1906 1908 1910 1912 1914 1916 1918 1920 1922 1924 1926 1928 1930 Publication Year of Citing Articles

Fig 3 Time-dependent number of citations of the 1900/1901 articles by Planck on energy quantization [9-11] and of the 1905 paper by Einstein dealing with the light quantum hypothesis and introducing the photon [25].

articles past 1920 are reviews and/or mainly discuss Planck’s The time evolution of citations is a result of two competing constant in an historical or philosophical context. The classical phenomena: the aging of the articles (obsolescence, papers establishing quantum mechanics (by Heisenberg, replacement, oblivion) and the growth of the scientific Schrödinger, Born, Dirac, Pauli, and Jordan) received many literature. The articles covered by the SCI as well as by more citations within the first years after their appearance. INSPEC increased approximately by a factor of hundred Based on the WoS Cited Reference Search mode and the time throughout the 20th century. The proliferation of science period 1880-1950 (the publication years relevant for Planck), implies a proliferation of potentially citable articles, resulting we determined the time curve of the overall number of in increasing ratios of references per article (reference count) citations of all publications by Planck (articles as well as books and therewith of the average number of citations per article and any other published material) as shown in fig. .4 Such (citation rate). We may speculate about how much more a seminal work is often cited by mentioning the author’s name citation around 1900 is worth compared to a present day or name-based items (informal citations [26], also called citation and may decide that citation numbers have inflated eponyms) instead of citing the full references as a footnote by a factor between ten and hundred. (formal citations). Therefore, we included in fig. 4 the separate Finally, we summarize the citation analysis by listing the time curve of the informal citations based on the INSPEC citation numbers with respect to articles and books and to database (“Planck” appearing in the titles, the abstracts or articles only, for the time period January 1900 to June 2008: the keywords). The time curve of the total number of records • Impact of articles only based on the WoS General Search covered by INSPEC is shown as an illustration of the time mode: 679 citing papers comprising 840 citations evolution of the physics literature. (citations of the pre-1900 articles not covered by the WoS Out of almost 16,000 articles mentioning Planck’s name, as source records are excluded). about 8300 refer to the so-called Fokker-Planck equation. The • Total impact (pre-1900 articles and books included) based Fokker-Planck equation describes the time evolution of the on the WoS Cited Reference Search mode: 2767 citing probability density function of the position and velocity of papers comprising approximately 3000 citations (some particles. Planck derived the equation, already independently papers cite more than one Planck article and/or book). reported in 1914 by Adriaan Fokker (1887-1972) [27], which • Impact of articles published in Sitzungsberichte der has become most important for statistical mechanics. Note the Preußischen Akademie der Wissenschaften and in large difference between the formal citations of the original Verhandlungen der Deutschen Physikalischen Gesellschaft papers (Planck: 117, Fokker: 132) and informal citations (8300). altogether 674 citations.

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Formal vs Informal Citations of Max Planck 900

800 Formal Citations - W oS Informal Citations - W oS 700 k Informal Citations - INSPEC nc s la 600 INSPEC Total (x 1/1000) le P ic rt ng 500 ni f A io o er

ent 400 m mb / 300 Nu ng ti

ci 200

100

0 90 00 10 20 30 40 50 60 70 80 90 00 10 18 19 19 19 19 19 19 19 19 19 19 20 20 Publication Year of Articles citing / mentioning Planck

FIG 4 Time dependent number of formal citations referring to the works of Max Planck (articles and books) versus informal citations (“Planck” appearing in the titles, the abstracts or the keywords) based on INSPEC. The time curve of the total number of records covered by INSPEC is shown as an illustration of the time evolution of the physics literature. Currently, the publication year 2007 under INSPEC is not complete and hence not included here.

The large difference between I and II is caused by (1) the of the WoS General Search mode. In this mode only the pre-1900 articles which are not covered by the WoS, (2) the citations of the papers covered by the WoS source journals are various Planck publications which did not appear in WoS included. The h-index of Max Planck rises from 12 to 14 if the source journals (e.g. some articles, books, lectures, and talks), citations to the pre-1900 articles not covered by the WoS are and (3) the above average citation error rate due to the taken into account. specific history of Planck’s most important journalAnnalen Note that the impact of early papers, and thereby the der Physik (see above). h-number of pioneers like Max Planck are much lower than those of current top-scientists (e.g., P. W. Anderson, h = 103; Planck’s h-index Giorgio Parisi, h = 77). The increasing number of citable A new index (h-index, h-number) was introduced recently papers within the last century results in increasing average by Jorge E. Hirsch as a measure of the cumulative impact citation rates. In addition, the h-index is a measure both for of a person’s scientific work within a given discipline [28]. It performance as well as output. The publication habits (in can be easily obtained under the WoS General Search mode, particular the average number of papers per year and the provided there are either no highly cited namesakes or they number of coauthors per paper) have increased significantly. can be removed. The h-index is simply defined as the number Around 1900 scientists like Planck used to publish 1-2 articles of articles in source journals that have had h citations or more. per year. Hence, the citation numbers (and the h-numbers) The index increases roughly linearly with the scientific age of of early scientists are not directly comparable to those of the scientist and depends on his specific research field. The present-day researchers. h-index reflects a researcher’s contribution based on a broad In general, research evaluation, particularly where individuals body of publications rather than based on a few high-impact are involved, has to be done very carefully, because one is papers. This avoids an overestimation of single or few highly dealing with people’s careers. This caveat does not apply to cited papers, sometimes being methodological contributions, early pioneers, but in their case the danger of distortion is reviews or articles with a number of coauthors in which it is even larger. impossible to assign individual contributions. The h-index favors researchers who consistently produce influential Planck’s books and published lectures papers. Planck was one of the leading theoretical physicists at his The h-indexes given in tab. II were determined on the basis time. Not surprisingly, his lectures given at the University of

52 < il nuovo saggiatore m. cardona and W. Marx: max Planck - A conservative revolutionary

Berlin appeared as books. In addition, Planck became one of by the sociologist Robert K. Merton [33-34]. The process of the most important representatives of German science. His obliteration or palimpsest (the latter expression referring to many talks given in his role as permanent secretary of the a piece of parchment used more than once, i.e., being erased Prussian Academy of Sciences, as rector of the University of to make room for newer work) affects seminal works i.e.( , Berlin, and as president of the KWG have been published. truly ground-breaking research) offering novel ideas that Planck’s books can be classified into the following categories: are rapidly absorbed into the body of scientific knowledge. • Scientific autobiography [1] and the various biographical Such work is soon integrated into textbooks and becomes notes. increasingly familiar within the scientific community. As • Dissertation, Habilitation, and Nobel lecture. a result of the absorption and canonization, the original • Lectures published in book form and given in ref. [29-32]. sources (mainly articles or books) fail to be cited, either as full • Talks (about science, philosophy, and religion) collected in references (formal citations) and even as names or subject ref. [8]. specific terms (informal citations) [26]. Books or book articles are no WoS source records and are The ideas survive sometimes becoming substantial therefore not searchable via the WoS General Search mode. elements of the basis and groundwork of modern science, The references assigned to books within the articles of the but overbuilding the groundwork implies obliterating the WoS source journals, however, are completely captured in sources. For example, the articles of Albert Einstein on the the WoS. The citations of individual books (and of articles Theory of Relativity (published 1905 and 1916, respectively) not published in source journals) are determined using the are rarely cited in current research papers (as compared WoS Cited Reference Search mode. As a result of our analysis, to less fundamental work), although they are the basis of Planck’s lectures received altogether almost 700 citations. See modern cosmology and mainly caused Einstein’s popularity. for comparison Richard Feynman’s famous Lectures on Physics It may even happen that a transmitter, being familiar with the (4500 citations). Planck’s scientific autobiography was cited origin of a concept and assuming that the same is true for his about 200 times. We should mention here that citations do readers, brings the idea back to life without citing the source not measure the full impact of books, but only the reference and eventually becomes identified with its originator. based attention within the ensemble of articles published Eugene Garfield, the inventor of the citation indexes and in the WoS source journals. In contrast to books, research the founder of the ISI (Institute for Scientific Information, articles can be much better evaluated by this method. Philadelphia), concisely stated in one of his essays [35]: “Obliteration – perhaps even more than an astronomical Obliteration by incorporation citation rate – is one of the highest compliments the The works of Max Planck, in particular those in the community of scientists can pay to the author…. It would field of quantum physics (but also his contributions to mean that his contribution was so basic, so vital, and so well- thermodynamics), are a typical example of “obliteration known that scientists everywhere simply take it for granted. by incorporation”, a phenomenon first described in 1949 He would have been obliterated into immortality”. Bearing that in mind, we should not expect that the formal or even the informal citations of the works of Max Planck can be taken as a real measure of the influence of his ideas in modern Researcher h-number science. There is no metrics for quantifying fundamentality, Max Planck 12/14* significance or even elegance, which are terms belonging to a completely different category. Wilhelm Wien 10/13* Niels Bohr 22 4 Conclusions Albert Einstein 46 We have considered Max Planck not only as a towering Enrico Fermi 31 scientist, one of the fathers of modern physics, but also as a prominent historical figure, a witness, an actor and a tragic * h-number corrected with respect to the pre-1900 articles not covered as source records by the WoS (under the General Search victim of some of the major cataclysms of modern history. In mode). They have been estimated using the Cited Reference his public political life he was confronted with overwhelming Search mode. dilemmas. His handling of them has been the object of considerable controversy, especially in recent years, a fact Tab. II Comparison of Max Planck with some Nobel laureate which is not privy to him but also applies to many of his contemporaries by using h-numbers. “Aryan” German contemporaries. His main contributions to

vol24 / no5-6 / anno2008 > 53 science, especially his treatment of the black-body radiation [14] J. C. Mather et al., “A preliminary measurement of the cosmic and his introduction of Planck’s constant h and Boltzmann’s microwave background spectrum by the cosmic background explorer (COBE) satellite”, Astrophys. J., 354 (1990) L37. constant kB, have been discussed. Citation analysis has been [15] M. Planck, “The theory of heat radiation”, Ann. Phys. (Leipzig), 336 applied to his published works and shown to be of limited (1910) 758. value, a fact which also applies to other old pioneers. The [16] T. S. Kuhn, “Black body theory and the quantum discontinuity” (New concept of informal citations (eponyms) brings better to the York, Oxford) 1978. [17] D. Hoffmann, Max“ Planck und Albert Einstein – Kollegen im fore his present-day impact. Widerstreit“, Spectrum der Wissenschaft, 5 (2008) 32. [18] M. Cardona and W. Marx, “Max Born and his legacy to condensed matter physics”, Ann. Phys. (Berlin), 17 (2008) 497. [19] URL Thomson Reuters: References http://scientific.thomsonreuters.com/products/wos/ [20] URL STN International: http://www.stn-international.de/ [1] M. Planck, “Scientific autobiography” (Philosophical Library, New [21] “Planck’s Annalen publications (1881-1941)”, Ann. Phys. (Berlin), 17 York) 1949. (2008) 68. M. Planck, “Autobiografia scientifica, La conoscenza del mondo [22] A. Einstein, B. Podolsky, and N. Rosen, “Can quantum-mechanical fisico” (Bollati Boringhieri, Torino) 1993, pp. 11-32. description of physical reality be considered complete?”, Phys. Rev., 47 [2] J. L. Heilbron, “The dilemmas of an upright man – Max Planck as (1935) 777. spokesman for German science” (University of California Press, [23] A. Einstein, “A new determination of the molecular dimensions”, Ann. Berkeley and Los Angeles) 1986. Phys. (Leipzig), 19 (1906) 289. [3] A. Hermann, “Planck, mit Selbstzeugnissen und Bilddokumenten“ [24] A. Einstein, “A new determination of the molecular dimensions (Rowohlt Verlag, Reinbeck bei Hamburg) 1973. (correction)”, Ann. Phys. (Leipzig), 34 (1911) 591. [4] D. Hoffmann, Max“ Planck - Die Entstehung der modernen Physik“ [25] A. Einstein, “Generation and conversion of light from a heuristic point (Verlag C. H. Beck, München) 2008. of view”, Ann. Phys. (Leipzig), 17 (1905) 132. [5] D. Hoffmann, ...you“ can’t say to anyone to their face: your paper is [26] W. Marx and M. Cardona, “The citation impact outside references rubbish.” – Max Planck as editor of the Annalen der Physik, Ann. – formal versus informal citations”, Scientometrics, Phys. (Berlin), 17 (2008) 273. [27] A. D. Fokker, “The median energy of rotating electrical dipoles in [6] A. von Pufendorf, “Die Plancks: Eine Familie zwischen Patriotismus radiation fields”, Ann. Phys. (Leipzig), 43 (1914) 810. und Widerstand” (List Verlag, Berlin) 2007. DOI: 10.1007/s11192-008-1824-2 [7] H. Kragh, “Max Planck: the reluctant revolutionary”, Physics World, 13 [28] J. E. Hirsch, “An index to quantify an individual’s scientific research (2000) 31. output”, Proc. Natl. Acad. Sci. U.S.A., 102 (2005) 16569. [8] M. Planck, “Physikalische Abhandlungen und Vorträge”, no. 1-3 [29] M. Planck, “Einführung in die theoretische Physik“, no. 1-5 (Leipzig) (Vieweg Verlag, Braunschweig) 1948. 1916-1930. [9] M. Planck, “Über eine Verbesserung der Wien’schen [30] M. Planck, “Vorlesungen über Thermodynamik“ (Veit, Leipzig) 1897. Spektralgleichung”, Verhandlungen der Deutschen Physikalischen [31] M. Planck, “Vorlesungen über die Theorie der Wärmestrahlung“ Gesellschaft (1900) 202. (Barth, Leipzig) 1906. [10] M. Planck, “Zur Theorie des Gesetzes der Energieverteilung im [32] M. Planck, “Acht Vorlesungen über theoretische Physik”, held at the Normalspektrum”, Verhandlungen der Deutschen Physikalischen Columbia University, New York 1909 (Hirzel, Leipzig) 1910. Gesellschaft (1900) 237. [33] R. K. Merton, “Social theory and social structure” (The Free Press, [11] M. Planck, “The energy distribution law of the normal spectrum”, Ann. New York) 1968. First edition 1949. Phys. (Leipzig), 309 (1901) 553. [34] R. K. Merton, “On the shoulders of giants: a Shandean postscript” [12] A. Hermann, “Frühgeschichte der Quantentheorie“ (Physik Verlag, (The Free Press, New York) 1965. Mosbach) 1969. P. 31: Letter to Robert Williams Wood (1931). [35] E. Garfield, The“ obliteration phenomenon in science – and the [13] M. Planck, “History of the retrieval of the physical quantum of action”, advantage of being obliterated”, Essays of an information scientist, 2 Naturwiss., 31 (1943) 153. (1975) 396.

Manuel Cardona Werner Marx Born 1934 in Barcelona, Spain. Licenciado en Ciencias, Barcelona, Born 1951 in Trier, Germany. Diploma in Physical Chemistry 1955; Doctor en Ciencias, Madrid, 1958; Ph.D., Harvard, 1959; worked 1978, Doctoral Thesis (PhD) 1981, University of Bonn, with both at RCA (Radio Corporation of America) Laboratories, Princeton and dissertations on atmospheric chemistry (ozone depletion). Joined Zürich, 1959-1964; Associate Professor (1964-1968) and Professor the Max Planck Institute for Solid State Research in Stuttgart in 1982 of Physics (1968-1971), Brown University; Founding Director, Max as information specialist. Since 1994 head of the Central Information Planck Institute of Solid State Research (1971-2000), from 2000 Service for the institutes of the Chemical-Physical-Technical (CPT) Director Emeritus; Member of several academies including: National Section of the Max Planck Society. Special interests: bibliometrics, Academy of Sciences of the USA (1988), Academia Europaea (1991) scientometrics and the history of science. Author or coauthor of and Accademia Nazionale dei Lincei (foreign member, 2008); Dr. about 20 scientific papers analyzing seminal publications, prominent h.c. Università di Roma La Sapienza (1995). Author or coauthor of scientists, and scientific journals using bibliometric methods. about 2200 scientific articles and a textbook: Fundamentals of Semiconductors (with P. Y. Yu, fourth edition).

54 < il nuovo saggiatore percorsi

FRESNEL, THE PRINCE OF THE OPTICIANS

Roberto colella Physics Department, Purdue University, West Lafayette, Indiana, USA

Augustin Fresnel died on July 14, 1827, at the age of 39. We will try in this short article to illustrate the amazing transformation his genius was able to bring about by his tremendous activity over a period of nine years, so suddenly interrupted by his disease and death. One of the past directors of the French Lighthouses remarked that this astonishing genius was able to display the same innovating creativity in the practical domain, with the result of bringing about a complete transformation in the way in which light, guide to sailors, is utilized and produced.

At the beginning of the XIX century the nature of light was not entirely clarified. Many beautiful experiments performed by Fresnel and others supported the wave theory, but several other equally beautiful experiments could not be shown to fit the wave picture. Things got worse towards the end of the century. It was in fact in 1900 that Planck introduced into radiation theory the famous quantity h, the quantum of action, which allowed to understand a large body of spectroscopic work, thanks to the works of Einstein, Sommerfeld, Bohr, and many others. It was in 1881 that Michelson published the negative result of his wonderful experiment: the Earth’s motion does not modify at all, not even in second order, that is to say, within one part over 1010, the speed of light. To say the truth, the incompatibility of this result with the whole body of classical theories was not immediately apparent. It was enough to give up the idea of an absolutely still and universal ether, postulated by Lorentz, and to

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admit, following an old suggestion by Stokes, that all celestial bodies, the Earth, for example, can drag the surrounding ether. A certain intermediate distance could be defined at the separation point between an ether fully dragged by the Earth’s surface (Michelson), and an ether at rest with respect to the fixed stars (or at least, to the Solar System). Only later did the difficulties of this single and attracting hypothesis become clear, and all scientists gave it up. Fresnel was born on May 10, 1788. He was admitted to the “École Polytechnique”, created in 1795, at the age of sixteen and a half years, in 1804. Arago was admitted the previous year, and had started at this time a friendly relationship with Poisson, who was the first to graduate from this school in 1800. He became a professor of mechanics in 1802, and used to live in the building of the school. Fresnel graduated in 1806, then applied for admission in the school of Highways and Bridges, and became an engineer in 1809. Between 1809 and 1815, in the departments of Vendée and then of Drôme, he was continuously kept busy with the most unpleasant jobs, such as supervising road repairs, searching for stone jot down an outline for the theories described in two papers banks , making sure that they were evenly distributed along sent to the Academy of Sciences in October and November. the ruts in the roads, maintenance of small irrigation canals, In 1816 he is put in charge of a demanding job in Rennes, so and particularly checking on hourly slips and measures that he must stop his experiments. He will be granted a leave on earthwork. Hard work for his weak body and for his of absence in 1827 which will allow him to go back to Paris, intelligence, so opposed to any form of management of where he will live for the rest of his life. At the beginning of people. 1818 he is associated with the Ourcq canal. The Hundred Days brought some spare time to him. The forced vacation brought about by the Hundred Days Convinced royalist, Fresnel joined voluntarily the little allowed Fresnel’s imagination to develop in full ferment. incongruous forces who, under the leadership of the Duke He was well advised by his uncle Léonor Mérimée who had d’ Angoulême , tried to stop Napoleon’s triumphant recently written to him (January 17, 1814): “We are led to march from the Elbe island. Fresnel was subjected to strict believe that there are no more discoveries to be done, for the disciplinary rules, executed without too much rigor by the reason that every substance in the world has been handled count Réal, police chief during the Hundred Days. He was and treated in such a way that not much is left for us to forced to take some rest at his mother’s estate in Mathieu, play with. However, from time to time, there are discoveries Eure department. It was at this time that he performed his which prove that something is left to feed human curiosity. first measurements on the hyperbolic progression of the Therefore, do not put aside any new idea you may come diffraction fringes, using rudimentary tools such as string across”. and razor blades. He started to work in Optics with an How Fresnel followed this advice and “fed human curiosity” entirely new attitude. In fact, it is well known that his physics will be described later in this article. professor at the École Polytechnique was rather ignorant. It was then at the age of 27, after six years of service as an Fresnel did not know English; he was unaware of the engineer, without any experimental background, without a experiments and hypotheses of Thomas Young. The French laboratory to speak of, that Fresnel tackled the problem of textbooks by Libes and Haüy made hardly any mention to measuring with great accuracy the positions of diffraction those topics. fringes. It is interesting to follow, through the chronological In the beginning Fresnel was intrigued, through a list of his publications, the extraordinary fast sequence of conversation with Arago, by the phenomenon of stellar his discoveries. Nine years (1815-1824) were enough for aberration, and by the experiment involving an astronomical him to create the optical theory of waves, crystal optics, telescope filled with water. and to keep busy three following generations of scientists, Fresnel arrived at Mathieu in April, 1815. Only at the end of some of them very eminent ones. After June 1819 up until the year was he called back to active duty. These six months his death, in 1827, Fresnel was a member of the Committee had been enough for him to perform some experiments and of Lighthouses, and never stopped his scientific and

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works executed during the XIX century. The same can be said of all numerical relationships between observable quantities deduced by Fresnel using general arguments based on wave theory. However, in order to determine in some instances the appropriate mathematical corrections, and to put his arguments, in all cases, on solid footing, a whole century of efforts has not been too much. In any big topic tackled by Fresnel, he always aimed straight at the main point, well delineated, which he wanted to reach without being distracted by excessive demands of logical rigor. He knew how to choose his postulates to be used in the ensuing computations, without worrying too much about their number. He was satisfied with persuasive arguments to justify their internal consistency and their compatibility with the fundamental principles of wave theory. And always his postulates led him without hesitation to wonderful formulae in amazing agreement with the most unpredictable facts. Well known examples are i) the bright point at the center of a small disk, administrative activity in the optical design of stepped lenses, ii) the elliptical polarization by total reflection, catoptric and dioptric, methods of fabrication, improvements iii) the circular birefringence of quartz along directions close on their brightness, the regular motion of pulsed lighthouses, to the principal axis. etc. His productivity is astonishing. Between 1816 and 1824 The nature of light was the source of great controversies he published 25 papers in which he revolutionized the whole which were settled (so to speak) only around the middle of field of optics. The papers deal with many basic issues in the XIX century. One theory was: light is waves (Huyghens, disparate fields such as diffraction, interference, polarization, Young, Fresnel); the other theory was: light is material double refraction. One of these papers was a sealed particles (Newton: emission theory). It is interesting to see message to the Academy of Sciences, dated April 20, 1818, that Newton himself developed a theory of tides based on on the theory of diffraction. This was the classical theory of the principles of interference. It is a theory often mentioned diffraction, due to Fresnel, with a table of numerical values for by Young, who believed that the same theory could be the Fresnel integrals: applied to explain light, contrary to Newton’s ideas. It is an attempt to explain certain anomalous tides observed by Halley in the China Sea, presented in the third book of “Principia” (chapt. 24). According to Newton the waves of the ocean tides would penetrate into the China Sea through two Some of these papers were written in response to objections narrow passages located north and south of the Philippines raised by Poisson in regard to the controversy about the Archipelago. In the harbors in which the two tidal waves were nature of light: waves or particles? On May 12, 1823, Fresnel delayed, one with respect to the other, by 6 hours, they would is unanimously elected member of the Academy of Sciences, destroy themselves. No destruction would take place when succeeding Charles (who had been a member since 1795). the two tidal waves were out of phase by one whole day, After 1821 up to 1824 Fresnel had to spend many hours for a which was the case when the moon was in the plane of the meager profit, as a “temporary examiner” of the students from equator. The time of his forced exile in Mathieu was dedicated the Polytechnic School. From the end of 1824 on, his failing entirely to study the principles of diffraction theory. Fresnel health allows him just to continue his lighthouse service, but understood that the phenomena of shadows presented he is no longer able to pursue his scientific research. Only a some aspects that could not be reconciled with emission few months before his death, at the beginning of 1827, he theory, and he realized that a thorough understanding of obtains to be helped by his older brother Léonor Fresnel, also these aspects was important. In his isolation, Fresnel had from the Polytechnic School like himself. no micrometer which would have enabled him to measure In order to appreciate Fresnel’s amazing intuitive power, we the width of the fringes he was planning to observe. He had must remember that all results of his experiments have been no heliostat to stabilize the direction of the light beam. He confirmed by the most accurate and extensive experimental himself fabricated a micrometer, using wires and cardboard

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pieces. He was able to greatly reduce the inconvenience due the first case, the intensity was the same intensity obtained to the apparent motion of the sun by making use of a lens with the disk removed, in the second case the intensity was with short focal length. The locksmith of the little town of close to zero for several values of the distances source to Mathieu built for Fresnel some structural supports, and, by aperture. These distances could be calculated by means of a making use of this primitive equipment, Fresnel was able, simple formula. Fresnel was invited to provide experimental with a lot of patience and care for small details, to obtain evidence for these two cases. He had to improvise both results sufficiently accurate for establishing some of the experiments, and in both cases he was able to get spectacular most important laws of Optics. Two long papers, presented agreement between his theory and the experiments. to the Academy of Sciences with an interval of a few weeks, Posterity has ratified the sentence of the Academy, and even were the early reports of these research activities. Diffraction half a century after the competition of 1818 Fresnel’s report studies started with investigating the shadows; the principle was universally considered one of those eternal masterpieces, of interference was discovered by Fresnel through the worthy to be studied in detail even a long time after it was no observation of the shadows projected by a thin wire. The longer at the forefront of research. key point is: what happens at the superposition of different Looking at Fresnel’s last publications, it is clear that his output waves? This is the point which contradicts Newton’s theory was considerably reduced during the last four years of his life. and confirms the wave theory. In Fresnel’s words: “It is clear There is no question that his health was rapidly deteriorating that the vibrations associated with two rays crossing at a to the point of making it impossible for him to continue his small angle may result in zero intensity when the nodes of research activities in which his genius had been able to reap one ray correspond to the antinodes of the other ray”. so many triumphs and successes. But the main reason for his The phenomena about diffraction discovered by Grimaldi, decrease in research activities was to be found elsewhere: it and later by Hooke and Newton, had been the subject of was the ever increasing duties in his engineering activities. research for several scientists, such as: Young, Fresnel, Arago, Do not forget that Fresnel’s profession was: “Engineer at the Pouillet, Biot et al. They observed the diffracted fringes which School of Highways and Bridges”. He was called, in the spring are formed and propagate outside of the shadows of certain of 1818, to supervise the construction of the Ourcq canal, but objects. They considered the fringes formed within the did not keep for a long time that position. In May 1819 he shadows, which are formed when the light rays propagate was transferred to the register of the survey of lands for the simultaneously around the two sides of a very thin object paving of the city of Paris. But the administration of Highways (a thin wire, for example), and also those fringes which are and Bridges realized that they could get some advantages formed by reflection on the surface of a limited extent, when by hiring an engineer who was revolutionizing the optical the incident and reflected rays propagate very close to their science from top to bottom, so, on June 21, 1819, Fresnel was edges. The competition between wave theory (Huygens, attached to the Commission of Lighthouses. This became Young, Fresenel) and emission theory (Newton, Laplace, his main occupation, and we can hardly imagine how much Biot, Poisson) was fierce. The French Academy of Sciences benefit the man who invented the reticular lenses was able to proposed a prize for the scientist who could demonstrate, transmit to his community. The thought comes to our mind. beyond any doubt, which theory (waves or emission) should Other engineers, sooner or later would have invented what be used to describe the nature of light. The scientists who we call now “Fresnel Lenses”, namely, the lenses with thick were contemplating to participate in the competition were steps which concentrate the light in flat spherical regions, but expected to set up experimental demonstration to provide only Fresnel could continue the revolution he had started in experimental evidence. Needless to say, Fresnel won the science. Who could predict what he would have done, if he competition. The vote of the Committee Members, which had been allowed to pursue without interruptions of any kind included three illustrious scientists who were initially in favor the free development of his creative imagination? He tried of the emission theory, was affected by the favorable attitude several times to start a new career, or to find in a job situation of people like Laplace, Biot and Poisson, three big names in more congenial with his interests the necessary resources the world of mathematics. A striking episode made a great needed to perform interesting optics experiments. The impact on the minds of the judges. Even though it did not expenses involved are quite substantial for the modest salary change most likely their way of thinking about the nature of of an ordinary engineer in Highways and Bridges. During light, it was probably the explanation of their unanimous vote the winter 1819-1820 he offered at the Atheneum a physics in favor of Fresnel. Poisson made the point that the integrals course, but he realized that teaching was not for him. In 1821 used by Fresnel to calculate the intensity of the diffracted he accepted the unattractive and low-pay job of “Temporary light could be evaluated exactly at the center of the shadow Examiner” for the students of the Polytechnic School. He of a small disk and at the center of a small circular opening. In kept this job after trying, with no success, to exchange the

58 < il nuovo saggiatore r. colella: fresnel, the prince of the opticians

1 2

position for a more lucrative job of examiner for the students be opaque or transparent. See fig. .1 The main idea of zone of the Navy School. He kept this position with the Polytechnic plates is to consider a point source, and, at some distance, School up to 1824. He had to resign for health reasons. At the regions of constant phase obtained by means of the this point he had lost the energy needed to carry on his own Huygens principle. Each ring, perpendicular to the direction scientific research and his engineering job. Being sensitive to of observation, has radii proportional to the square roots of his duties and to his feelings of faithfulness he had inherited whole numbers. The phase corresponding to each zone is from his parents, he sacrificed everything he might have done assumed to be constant over the annular region. This is an to seek personal glory and satisfaction, and dedicated to the important approximation. It turns out that the final results service of the lighthouses every moment of relief from his are the same as those obtained by considering infinitely sickness. It was only at the beginning of 1827 that he asked thin Fresnel zones, with phases defined as continuous for, and was granted permission to, be helped by his brother, functions, rather than step functions. A zone plate can be who later became his successor and took upon himself the described, therefore, as a special circular screen designed task of writing about this part of Fresnel’s science. But it was to block off the light from every other half-period zone. too late. Four months later, on July 14, 1827, Fresnel passed The result is to remove either all positive terms or all the away, in his mother’s arms. negative terms, when the overall illumination at any given Twenty five years before this happened, this pious and noble point is evaluated by adding up, in magnitude and phase, all woman, in expressing her wishes in regard to the future life the terms corresponding to the various Fresnel half-period of Augustin Fresnel, had these words to express from the zones. In this way the amplitude at any given point will be bottom of her heart: “I pray God that He will give my son the increased to many times its value obtained in the absence grace to make use of the great and many talents he received of a Fresnel zone-plate. Enhancement factors of 400 times or from God for useful gifts and the general welfare to be more can be easily obtained. It sounds paradoxical that by bestowed on humanity. Much will be demanded from whom inserting a screen, namely, by blocking off certain portions who received great favors, and much will be expected from of the incident intensity, we increase the local intensity, but whom who received great gifts”. this is the great intuition Fresnel had when he discovered the Who could satisfy better than Augustin Fresnel this desire to complete theory of diffraction of light, what we call today shower gifts on our neighbors? “Fresnel Diffraction”, as opposed to other mechanisms such as, for example, “Fraunhofer Diffraction”. Sometimes Fresnel zone plates are referred to as “Fresnel Fresnel, the inventor of gadgets Lenses”. The bright spot produced by a zone plate is so There is no question that Augustin Fresnel was one of the intense that the plate acts much like a lens. Fresnel lenses most able experimentalists of all times. Any optics book are routinely produced these days to be used for focusing will show in the subject index that the entry: “Fresnel” is the hard x-ray beams (10-15 keV) at 3rd-generation synchrotron longest one, encompassing in general between ten and radiation sources. Despite the name, Fresnel zone plates twenty items. A good part of these entries are gadgets used have not been invented by Fresnel. The first mention to in optics laboratories. One of the most popular gadgets is the the principle of increasing the light intensity by inserting a “Fresnel Zone Plate”. It is a circular aperture made with rings half-period zone between source and observer is found in of unequal radii. The central region of the zone plate may Lord Rayleigh notebook (April 11, 1871): “The experiment

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of blocking out the odd Huygens zones so as to increase the light at the center succeeded very well… .” There is no question, however, that the notion of zone plates and their behavior are entirely based on the new optical theory, much of which is due to Fresnel. It is fitting, therefore, to associate Fresnel’s name to the zone plates. Another gadget frequently used in optics laboratories is the so-called “Fresnel Rhomb”. It is a glass oblique-angled parallelepiped (see fig. )2 whose principle of operation is based on the fact that light beams internally reflected in the rhomb undergo well-controlled phase shifts. A plane-polarized light beam, falling perpendicular on the shorter surface of the rhomb, is shown to be circularly polarized when it gets out of the rhomb after two bounces of internal reflections. In other words, a Fresnel rhomb converts plane-polarized light into circularly polarized light. There are other devices capable of doing this. Let us not forget that the theory behind this particular scheme of operations was being developed in the early part of the nineteenth century. It was the theory of the new optics, based on the concept of waves and the Huygens’ principle. It is particularly significant therefore, that Fresnel actually constructed a glass rhomb of the form illustrated in fig. 2 and tested its behavior against theory. The general principles of interference are invoked many, many times in Fresnel’s “memoirs”. The basic notion that by by the source is a beam of thermal neutrons, for example. removing screens in an optical setup you do not necessarily We have mentioned several times, in the course of this increase the transmitted light, on the contrary, you quite article, Fresnel’s exceptional experimental ability. To really often decrease it, is a dominant theme in the “memoirs”. appreciate this point, we will now touch on his forced country One of the most direct experiments along this line is that vacation in Mathieu. Fresnel did not particularly welcome one based on two flat mirrors, called appropriately: “Fresnel Napoleon’s return from the Elba Island. The price he had mirrors”. It is a set of two identical mirrors, slightly rotated one to pay for his political orientation was an extended forced with respect to the other by 1-2 degrees. This way, a point vacation in a small country town: Mathieu, near Caen, where source is equivalent to two small, identical, very close point his mother had retired. Before going to Mathieu, however, sources. The two sources are coherent because they originate he was allowed to spend a few days in Paris, which enabled from the same source. In this case it is convenient to use a him to consult with some of the great scientist of his time, description of light in terms of “particles” (photons). Using particularly with Arago, his mentor. Fresnel realized that he inappropriate language (which leads, however, to a correct was facing a long period of isolation, so it was very important description) we can say that the splitting of images produced for him to get some advice from a great scientist like Arago, by the two mirrors has the effect of splitting each photon in who was in contact with the cutting edge of research of his two “half-photons” (so to speak). Each half-photon can only time. Fresnel decided in the end to dedicate his research interact with the other half, generated by the same photon, efforts to diffraction theory, while in Mathieu. Like Young, so interference effects (fringes) will appear. In other words, he had immediately recognized that the phenomena of this device, called “Fresnel mirrors”, is entirely equivalent to a shadows, which seemed to be the most difficult phenomena setup of two coherent sources. When one of the two mirrors to be explained by the wave theory, offered in the particular is taken away, the fringe system disappears. This proves that domain of diffraction, some irreconcilable difficulties for interference effects are present. The two descriptions, in the Newtonian theory of light. Fresnel had understood how terms of waves and photons, are equivalent. However, the important it was to acquire a detailed knowledge of these photon description can more easily be applied to situations contradictions. in which the wave description is problematic, namely, when In his isolation Fresnel had no micrometer to measure the the intensity is exceedingly weak, and the radiation emitted width of the fringes he was planning to observe. He had no

60 < il nuovo saggiatore r. colella: fresnel, the prince of the opticians

heliostat, to stabilize the sun rays on a constant direction. of honey on a small hole drilled in a copper sheet. This way, He fabricated himself a micrometer using some wires and Fresnel reports, it was possible to see sharp fringe images and pieces of cardboard. He was able to minimize the movements accurately measure their widths. of the sun by making use of a lens with short focal length. Fresnel’s ability to perform accurate measurements using The locksmith of the town built for him some supporting primitive equipment place him in the same class of people structures. He used them with great care and patience like Rutherford, Fermi, and others. Of Rutherford we will to get some reasonably precise results, which he used to remember the famous experiment which showed that helium revolutionize the optical theory. The results of these research was present in a glass tube which initially contained some efforts were described in two fundamental “Memoirs” to be radium. Of Fermi: we will remember his great intuition when presented by Arago to the Academy of Sciences, with an he decided, for no good reason, to shield a neutron source interval of a few weeks one from the other. using paraffin instead of lead, an experiment which initiated The starting point for Fresnel’s research efforts, we mentioned a whole new chapter in the development of neutron-induced earlier, was the study of shadows. His experimental technique radioactivity. Fresnel’s drop of honey in a copper plate is in consisted in making careful observations of the shadows the same category. projected by a thin wire, and correlating with the theory of interference. The most important component of the experimental setup was a micrometer Fresnel built with his Acknowledgments own hands. With this micrometer he could measure the width The author is indebted to his friend and colleague A. K. of shadows with an accuracy of 1 fortieth of a millimeter. Ramdas, who suggested the initial idea of this article, The micrometer consisted of two silk wires, issued from the and pointed out the interest for this subject. He was also same point and terminating at two points separated by instrumental in locating suitable graphic materials from his a distance of 5 mm. The observations were made with an rich collection. eyepiece of short focal length, placed in such a way that the wires were coincident with the focal point of the eyepiece. A small movable piece of cardboard was used to mark the position where the distance between the wires was equal to the width of the shadow. A great patience was required to use this rude micrometer, in which there was no calibrated screw. Another problem with this micrometer was that it could not be used to measure fringe widths greater than 5 mm. A better micrometer would have made life easier, but this crude instrument was the only one Fresnel could make with his own hands in a very short time. The results roberto colella of several measurements are neatly reported in tables, with Roberto Colella was born in Milan (Italy) in 1935. He received his complete explanations for the various columns of numbers. academic education at the University of Milan, where he obtaind Most of the fringe measurements were done using iron wire his doctoral degree in 1958. In 1961 he joined the staff of Euratom Nuclear Research Center at Ispra (Italy) as a Research Scientist in the 1 mm in diameter. The experimental skills with which the Solid State Division, with Dr. A. Merlini. In 1967 he came to the U.S. as measurements were executed are just unbelievable. a postdoctoral research associate at Cornell University, Department Fresnel realizes, at the end of a measuring cycle, that he of Materials Science and Engineering, with Prof. B.W. Batterman, where he stayed until 1970. needs to test the theory of shadows in the limit of a large He joined the Physics Faculty of Purdue University on September distance between source and iron wire. He decided to use, as 1, 1971, as an assistant professor. He was tenured and promoted to light source, a star, one of the brightest stars in the sky. Sure associate professor on July 1, 1975, and became a full professor on enough, his diffraction theory is fully confirmed in the limit July 1, 1977. During the academic year 1991-92 he was visiting professor at of an infinite distance between source and iron wire. To verify the University of Paris-Sud (Laboratoire de Physique des Solids - diffraction theory in the opposite limit, at short distance Orsay, France),and at the University of Paris VI and VII, Place Jussieu, between source and diffracting wire, a small hole in a metal (Faculte’de Mineralogie et Cristallographie), Paris, (France). sheet was initially used, placed close to a strong convergent His general field of research is in the area of diffraction physics, with applications to interferometry, and the phase problem in lens. To operate at shorter distances, Fresnel could not find diffraction. a converging lens of sufficiently small focal distance. Again, his experimental ability helped him out of this problem. He found a way to fabricate a small lens by depositing a drop

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CERIMONIA INAUGURALE XCIV Congresso Nazionale della Società Italiana di Fisica

Genova, 22 Settembre 2008

L. Cifarelli: Benvenuti alla Cerimonia consolidarsi oggi di numerose realtà nel forse anche per quella parte autocritica Inaugurale del XCIV Congresso campo delle tecnologie d’avanguardia. che a me compete, che la ricerca e i Nazionale della Società Italiana di Una scelta che può continuare a ricercatori devono essere incentivati, Fisica, in questa splendida cornice costituire un’opportunità per le giovani motivati e sostenuti a tutti i livelli come della Sala del Maggior Consiglio di generazioni perchè solo facendo una grande risorsa del Paese senza la Palazzo Ducale. Innanzitutto vorrei leva sulla cultura e sulle acquisizioni quale si è perdenti nella competizione dare la parola ai nostri padroni di casa scientifiche si potrà promuovere uno globale. E al tempo stesso avverto e per primo al Dr. Giacomo Ronzitti, sviluppo socialmente e ambientalmente l’esigenza che la politica e le istituzioni Presidente dell’Assemblea Legislativa sostenibile. Nella consapevolezza delle pubbliche siano più attente e concrete della Regione Liguria, che ci onora con non poche difficoltà che permangono nel mettere coerentemente in pratica le la sua presenza. ancora e che non ci sfuggono, Genova elaborazioni e i progetti che vengono e la Liguria dunque vogliono affermarsi dalla sfera scientifica. D’altra parte G. Ronzitti: Signori Presidenti Cifarelli e quale polo scientifico tecnologico sappiamo bene come questa sia una Giannini, Illustri Professori, gentili ospiti primario nel panorama Nazionale ed condizione fondamentale per favorire è con vero piacere che intervengo a Europeo. Ed è in questo contesto che una crescita armonica della Società questo XCIV Congresso Nazionale della mi piace ricordare con il simposio di che ci pone ogni giorno di fronte a Società Italiana di Fisica porgendo a oggi i 25 anni dalla fondazione del problemi inediti in ogni aspetto della tutti il cordiale saluto dell’Assemblea nuovo Dipartimento di Fisica che vita umana. Alle istituzioni dunque Legislativa della Liguria che mi onoro ha svolto e continua a svolgere un spetta questo duplice compito di di presiedere. Sono particolarmente importante ruolo da tutti conosciuto. supportare quanto più possibile la lieto che Genova, e con essa la Liguria, Siamo coscienti di quanto sia essenziale ricerca e ascoltarne la voce per tradurne ospiti un evento scientifico tanto oggi che ricerca scientifica, economia e al meglio le indicazioni sul piano significativo. La nostra regione ha da istituzioni procedano di concerto con il strategico e operativo assumendo le tempo raccolto la complessa sfida del comune obiettivo di favorire una nuova conseguenti decisioni sul terreno della futuro guardando ai nuovi orizzonti che qualità dello sviluppo dopo quello che politica economica e finanziaria. In si possono aprire attraverso la ricerca ha caratterizzato l’industrializzazione particolare ritengo davvero prioritari, scientifica e l’innovazione tecnologica del secolo scorso, uno sviluppo che oggi, gli orientamenti e le decisioni che per costruire spazi di sviluppo e di sia eticamente corretto e valido, oltre investono la questione energetica, tanto occupazione dopo la lunga crisi dei che economicamente possibile ed in relazione alla produzione quanto vecchi assetti produttivi, il declino equo. Per questo avvertiamo con forza in relazione ad un possibile risparmio dell’industria di stato e la difficile la necessità di “fare sistema” affinché energetico, con tutte le implicazioni stagione della riconversione e della in ogni settore l’uso ragionato delle scientifiche, economiche, sociali ed riqualificazione urbana e ambientale. risorse sia definito secondo un’agenda ambientali che questo comporta e Una scelta lungimirante fatta a cavallo di priorità che riconosca nella ricerca, in che non a caso avete posto al centro degli anni `80 e che ha visto una quella teorica come in quella applicata, di una delle qualificate Tavole per rinnovata collaborazione tra il mondo una delle sue prime istanze. Per tale dare soluzione ai moltissimi problemi dell’università, delle istituzioni e della motivo sento il dovere di dire qui, non ancora irrisolti e per aprire nuove produzione, e che ha reso possibile il per demagogia ma per spirito di verità e prospettive ad un mondo che talvolta

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Da sinistra: R. Briano, L. Cifarelli, G. Ronzitti, M. Giannini e M. Margini.

appare smarrito e in preda a convulse e un modo o nell’altro Genova sta tra di noi facciamo un confronto molto irrazionali fobie. Questa consapevolezza rientrando in circuiti di confronti, di più ravvicinato, perché le espressioni deve guidare sempre di più le istituzioni discussione, di accoglienza a livello della politica devono avere con la italiane ed europee e, sulla base del nazionale. Questa è una cosa che ci fa scienza, la ricerca e l’innovazione un principio di sussidiarietà, l’azione molto piacere. Ci fanno piacere anche rapporto positivo. Ho visto che voi fate delle Regioni e delle Amministrazioni altre cose: ci accorgiamo − quando una tavola rotonda molto importante, Locali, convinti che le scelte razionali abbiamo occasione di confrontarci, a cui certamente parteciperò, quella si fondano in primo luogo sul sapere discutere − del fatto che, per quanto sull’energia. Io ho qualche difficoltà a scientifico. Con questo spirito rinnovo riguarda i temi dell’università, della vivere in un paese in cui si è ripreso a a voi tutti il saluto dell’Assemblea ricerca, dell’innovazione e dell’industria discutere sulla necessità della presenza Regionale insieme all’augurio di buon un vecchio modello di relazioni, del nucleare, a livello d’industria, ma lavoro. Grazie. particolarmente fra università e anche a livello dei rapporti con altre industria, è arrivato al capolinea. Si realtà nazionali. Il discorso sul nucleare L. Cifarelli: Grazie, Presidente, per il avverte quindi fortemente l’avvento prescinde in parte dalla necessità di suo intervento. Vorrei dare adesso la di una fase nuova, e non soltanto per costruire o meno e dove costruire una parola al Dr. Mario Margini, Assessore restare in linea con altri paesi. Ritengo centrale in Italia, è piuttosto legato al ai Lavori Pubblici e ai Grandi Progetti che in realtà questo sia il problema: fatto che noi siamo al di fuori di queste del Comune di Genova, che ci porterà costruire una nuova modalità di tecnologie. La mia impressione è che ci il saluto del Sindaco Prof.ssa Marta relazione tra il mondo della ricerca sia un’approssimazione nell’affrontare Vincenzi. e dell’innovazione e il mondo della il problema che lascia un po’ stupiti, e produzione. penso che la scienza, la ricerca debba M. Margini: Prima di tutto grazie Abbiamo studiato protocolli d’intesa, darci una mano a trovare soluzioni di aver scelto Genova come sede di abbiamo un bellissimo protocollo giuste e importanti. Vi riporto un questa importante riunione e di questo d’intesa con l’università. Anche se penso episodio personale: nella mia iniziale Congresso. Questo salone da un po’ che siano molto importanti gli accordi esperienza politica la scelta Genova fu di tempo ospita molte significative di programma fatti a livello locale e a dettata da un valore personale, dal Prof. iniziative, questo vuol dire che in livello nazionale, sento l’esigenza che Pancini che certamente molti di voi

64 < il nuovo saggiatore conoscevano. Mi colpiva molto il tono Italia perché il numero di ingegneri modo giusto. Noi nel nostro piccolo dei suoi interventi quando affermava informatici che vengono “sfornati” col Dipartimento di Fisica, quindi nel la necessità di sapere quello di cui si è insufficiente alle nostre esigenze”. concreto, stiamo già portando avanti parla per poi decidere. Io penso che Quello stesso giorno hanno scritto collaborazioni molto forti, in particolare oggi l’Università, i ricercatori, coloro che che per accedere a Medicina c’erano abbiamo due protocolli d’intesa, che producono innovazioni in ogni campo 1300 domande, il rapporto è di 100 a hanno anche attivato delle borse di debbano instaurare con la politica 1300. Io non ho niente contro i medici, studio − quindi che danno lavoro ai e le istituzioni un rapporto alla pari. anzi penso che un paese che voglia giovani − in due settori importanti Un rapporto con chi può ricevere, ma svilupparsi ha certamente bisogno di del nostro territorio, uno di questi è la che può anche dare. Noi dobbiamo medici ma ha assolutamente bisogno ricerca sulle polveri sottili. Credo che guardare alle vostre specializzazioni, anche di scienziati, di ingegneri, di forse siamo stati tra i primi, in Italia, e ai vostri problemi, alle vostre proposte coloro che fanno della produzione un ci siamo confrontati anche con le altre con grande attenzione e con grande punto di riferimento per tanti. Per cui province, a fare una ricerca specifica interesse. Ora, si parla molto in il mio augurio di buon lavoro a voi, sull’origine di queste polveri sottili e questi tempi di globalizzazione, che e guardate che da un certo punto di non soltanto sul quantitativo (di fatto la è un processo attualissimo, ma è vista abbiamo un problema comune: io legge ci dice solo se lo superi, basandosi vero che è in atto da molti anni; una penso sempre che il nostro problema esclusivamente sulla percentuale di maggiore attenzione avrebbe quindi comune sia quello di stabilire una presenza) ma l’importante è sapere permesso di capire quello che stava nuova scala di valori in cui la ricerca, da dove derivano per poi decidere cambiando. Ovviamente guardiamo l’innovazione, la capacità di decidere su che cosa intervenire. Ebbene con attenzione a voi anche in modo un abbiano un posto centrale nel confronto con il Dipartimento di Fisica stiamo po’ strumentale poiché desideriamo politico e in quello istituzionale. portando avanti da quattro anni questa che Genova sia in molti settori punto importante ricerca e abbiamo scoperto d’avanguardia a livello nazionale: ad L. Cifarelli: Grazie. Do ora la parola cose molto importanti, che oggi si esempio nelle telecomunicazioni. alla Dr.ssa Renata Briano, Assessore leggono sui giornali quotidianamente, Inoltre come voi sapete, ci siamo all’Ambiente della Provincia, che ci ma spesso ci si dimentica anche da candidati ad avere un ruolo porta il saluto del Presidente della dove derivano questi dati. Per esempio importante nel settore dell’energia, Provincia Dr. Alessandro Repetto. nella nostra città c’è una quota di stiamo cercando di orientarci verso polveri sottili, sulla quale non possiamo quella che chiamano “l’industria R. Briano: Buongiorno a tutti e farci niente perchè di origine naturale, pensante”. E in questo processo benvenuti a Genova e nella nostra una quota è dovuta al traffico veicolare (senza dimenticare il manifatturiero Provincia di Genova. Vi porto il e non solo, un’altra alla presenza delle − perché ci sono tanti che pensano saluto dl Presidente della Provincia industrie, che nel nostro territorio sono che noi non riusciamo a trovare poi che si scusa, ma è fuori regione per anche diminuite − quindi anche questa gli operai per andare a lavorare nelle un impegno istituzionale. Io sono quota in qualche modo sta scendendo fabbriche manifatturiere, ma questo è l’assessore all’ambiente, mi occupo − ma una percentuale importante è tutto un altro ragionamento) ritengo di tantissimi temi e problemi del dovuta alla presenza del porto e delle che voi possiate dare un importante nostro territorio che hanno una stretta navi in porto che tengono i motori contributo. Dopodichè chiedo a tutti relazione con gli studi, le ricerche accesi durante la loro sosta. Sembra voi di fare uno sforzo, perché un Paese e il lavoro che l’Università, e non una banalità ma capire che il 30% delle che vuole cambiare, un Paese che solo l’Università, anche la ricerca nel nostre polveri deriva da questa attività vuole avere un suo posto nell’industria, settore industriale, stanno portando significa poi attivarci politicamente nell’innovazione, nella ricerca, è un avanti. Vi do soprattutto un augurio e amministrativamente per risolvere Paese che deve valorizzare molto di buon lavoro e credo che i risultati tutti insieme questo problema. Quindi queste competenze, queste attività, di questo vostro incontro che si tiene le amministrazioni devono lavorare questo modo di affrontare i problemi. nella nostra città saranno utili alle insieme per la risoluzione di questo Un fatto mi ha particolarmente colpito: amministrazioni per prendere delle problema. Stiamo lavorando, sempre qualche giorno fa mi ha chiamato decisioni. Infatti credo sempre che con il Dipartimento di Fisica, anche un amministratore delegato di le decisioni che gli amministratori per capire le ricadute in atmosfera un’importante azienda di Finmeccanica prendono debbano basarsi su dati e su dei vari inquinanti degli impianti e mi ha detto: “Noi abbiamo grandi una ricerca scientifica forte e avanzata industriali. Anche questo è importante difficoltà a stare a Genova e in che ci dia l’opportunità di scegliere nel per avere una mappa nella nostra

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città delle zone più colpite e per come Genova ed è inoltre il Presidente del la Fondazione Cassa di Risparmio, intervenire poi, anche nelle nostre Comitato Organizzatore Locale del spero anche di potere ringraziare la stesse attività quotidiane. La Provincia Congresso della SIF. Fondazione san Paolo cui ho chiesto rilascia spesso autorizzazioni alle recentemente un contributo e per industrie per la loro produzione: anche M. Giannini: Il Rettore Magnifico ultimo l’Oratorio di san Filippo, e come rilasciare queste autorizzazioni dell’Università si scusa ma questa questo mi dà l’occasione per ricordare è in stretta relazione con quanto mattina è impegnato con una seduta che questa sera alle 20.30 ci sarà un stiamo portando avanti come ricerca del Senato Accademico convocata già concerto nella Chiesa di San Filippo con l’Università. Secondo me una all’inizio dell’anno, quindi era difficile Neri, un’occasione per visitare una cosa importante su cui dobbiamo spostarla. Mi ha promesso che verrà chiesa e un oratorio che sono molto impegnarci insieme, comunità alla conclusione del Congresso e quindi spesso chiusi al pubblico, con una scientifica e amministrazioni, è di mi ha incaricato di porgere a tutti voi statua moto bella della Madonna che rendere queste ricerche comprensibili ai il saluto e il benvenuto dell’Università è posta in modo molto scenografico e cittadini. L’amministrazione ha bisogno di Genova che è ovviamente coinvolta il concerto è un concerto di lirica che di spiegare perché fa alcune scelte, e lo in questa operazione, non solo tramite spero apprezzerete. deve spiegare non sul “sentito dire”, sulla il Dipartimento di Fisica, che mi onoro Vi do il benvenuto, vi invito tutti demagogia, lo deve spiegare basandosi di dirigere, ma anche ci ha dato un ovviamente al Dipartimento di Fisica, lo sui dati oggettivi che voi producete, supporto sia finanziario, apprezzabile troverete interessante anche dal punto però dobbiamo anche semplificare visto le disastrate condizioni del di vista architettonico, molti di voi già il linguaggio di comunicazione bilancio dell’Università di Genova, sia lo conoscono, ma credo valga la pena verso i cittadini, altrimenti spesso la anche come servizi, per cui ci ha evitato di visitarlo per vedere come è fatto. demagogia, la polemica prendono di dover intervenire direttamente. Purtroppo chi ci sta dentro lo apprezza il sopravvento e ci troviamo tutti Cercherò di essere breve e passerò un pò meno, ma dal punto di vista travolti da queste questioni quando subito anche alla comunicazione estetico credo sia molto interessante. invece proprio la scienza è quella che più tecnica, dovrò purtroppo un Grazie di essere venuti e ci rivediamo ci aiuta a dare delle risposte concrete po’annoiarvi perché come Presidente oggi pomeriggio. e a giustificare anche le scelte che noi del Comitato Organizzatore insieme facciamo. Quindi anche io seguirò con al comitato abbiamo preso contatto L. Cifarelli: Ancora grazie. Vorrei interesse la tavola rotonda sull’energia. con una serie di enti e istituzioni dare inizio a questo punto a uno Il tema dell’energia è un tema che ci cercando e ottenendo una reazione dei momenti più tradizionali riguarda tutti quanti, a partire dalle positiva di aiuto, di incoraggiamento dell’inaugurazione del Congresso piccole azioni che noi amministratori e di sostegno. Quindi credo che sia Nazionale della Società Italiana di Fisica, tutti i giorni facciamo nelle scelte per opportuno ricordarlo anche se, come ossia alla Cerimonia di Premiazione la ristrutturazione dei nostri edifici, e di sempre succede, gli elenchi sono della SIF, che riguarda un certo numero quelli del patrimonio provinciale, quali un pò noiosi. Anzitutto gli Enti di di nostri Soci, giovani e meno giovani. ad esempio che tipi di tecnologia usare. Ricerca INFN, CNR, INFM, il Consorzio In primo luogo premiamo i Soci È difficile cambiare anche la mentalità Nazionale Struttura della Materia, Benemeriti (in società straniere questi delle amministrazioni in questo senso. tutti gli enti locali Regione, Assemblea sarebbero i cosiddetti Fellows), nominati Quindi quello sull’energia è un tema e la Giunta, Provincia e Comune e dal Consiglio di Presidenza della SIF che ci riguarda: come hanno detto sia ringrazio in maniera particolare i loro per l’anno 2008. I Soci Benemeriti il Presidente del Consiglio Regionale rappresentanti che sono qui stamattina riceveranno un diploma e una medaglia Ronzitti che l’Assessore Margini infatti il per la loro presenza e per le parole per i loro contributi dati alla Scienza e tema dell’energia è un tema d’interesse d’incoraggiamento nei confronti alla Società Italiana di Fisica. nazionale e internazionale. dell’Università e del Dipartimento in In ordine alfabetico vorrei chiamare E di fatto ci riguarda anche nelle particolare, la Fondazione Palazzo innanzitutto il Prof. Enrico Bellotti piccole azioni concrete che portiamo Ducale che ci ospita e che ha messo dell’Università di Milano Bicocca, Socio avanti tutti i giorni, per questo quindi a disposizione questa splendida sala Benemerito per i contributi dati alla seguiremo, come Provincia, con per l’inaugurazione, la Confindustria Scienza e alla Società Italiana di Fisica, interesse i vostri dibattiti. Genova che ci ha dato supporto, visto in particolare nel campo dell’Astrofisica che si tratta di industriali genovesi Particellare. L. Cifarelli: Grazie. Adesso la parola va è stato un esploit non da poco, il al Prof. Mauro Giannini che rappresenta Festival della Scienza e gli Amici del E. Bellotti: Essendo, come sai, molto il Rettore dell’Università degli Studi di Festival della Scienza, il Museo Luzzati, affezionato alla Società Italiana di Fisica,

66 < il nuovo saggiatore porgo tanti tanti auguri a te come V. Degiorgio: Vi ringrazio moltissimo C. Rizzuto: Ringrazio la SIF per questo Presidente e a tutti. e vorrei solo augurare a tutti tempi riconoscimento e per tutto quanto migliori per l’Università e per la ricerca. sta facendo per la fisica italiana. L. Cifarelli: Grazie. Vorrei adesso Riferendomi ad alcuni precedenti Chiamare il Prof. Enzo Boschi L. Cifarelli: Chiamo ora il Prof. Giovanni interventi, però, vorrei sottolineare dell’Università di Bologna, Socio Ricco dell’Università di Genova, Socio che parlare solo di ritorno di tempi Benemerito per i contributi dati alla Benemerito per i contributi dati alla migliori non basta, perché questo Scienza e alla Società Italiana di Fisica, in Scienza e alla Società Italiana di Fisica, dipende dall’impegno che viene messo particolare nel campo della Geofisica. in particolare nel campo della Fisica nel costruire condizioni migliori. Ad Nucleare. esempio, la SIF e la fisica italiana sono E. Boschi: Volevo ringraziarti, state estremamente impegnate nel ringraziare la Società Italiana di Fisica, G. Ricco: Sono molto lusingato di costruire istituzioni a livello europeo perché è un riconoscimento molto ricevere questo riconoscimento proprio dagli anni `50 e `60 fino agli anni `70, importante, tenendo conto anche nel cuore storico della mia città, mi ma adesso sia la fisica che l’Italia in che viene da persone che stanno per auguro di poter continuare a contribuire generale sono molto assenti. In assenza riprodurre l’origine dell’universo, quindi nel settore nucleare, soprattutto nel di impegni personali e continui, i tempi siamo tutti emozionati. Speriamo che la settore dell’energia nucleare, che dopo migliori non ritorneranno per conto loro. macchina funzioni presto e che presto tanti anni di silenzio sta tornando di possiamo risolvere questo problema, nuovo di grande attualità. Grazie ancora L. Cifarelli: Vorrei chiamare infine il che anche noi geofisici aspettiamo da e tanti auguri al nostro Presidente. Prof. Andrea Taroni dell’Università di tempo. Castellanza, Socio Benemerito per i L. Cifarelli: Per fluttuazione statistica contributi dati alla Scienza e alla Società L. Cifarelli: Grazie. Vorrei chiamare il abbiamo anche un altro genovese, Italiana di Fisica, in particolare nel Prof. Vittorio Degiorgio dell’Università di il Prof. Carlo Rizzuto dell’Università campo dell’Elettronica. Pavia, Socio Benemerito per i contributi di Genova, Socio Benemerito per i dati alla Scienza e alla Società Italiana contributi dati alla Scienza e alla Società A. Taroni: Ringrazio di cuore la di Fisica, in particolare nel campo della Italiana di Fisica, in particolare nel Società Italiana di Fisica per questo Fisica della Materia. campo della Luce di Sincrotrone. riconoscimento. Sono lusingato,

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sorpreso, felice; anche se normalmente giant branch stars.” Secondo premio al “Caratterizzazione Raman risonante ricevere un premio come quello di Dr. Fabio Cappella del Dipartimento e meccanica di singoli globuli rossi oggi induce a credere che si stia di Fisica dell’Università di Roma “La manipolati con una pinzetta ottica.” entrando nella terza, non voglio dire Sapienza” e dell’INFN, Sezione di Roma Secondo premio al Dr. Daniele Panetta età, ma almeno fascia di attività come 1, per “Da DAMA/NaI a DAMA/LIBRA e del Dipartimento di Fisica dell’Università ricercatore. Grazie ancora. oltre”. di Pisa e dell’INFN, sezione di Pisa, per “Caratterizzazione di un prototipo di L. Cifarelli: Passo ora, ancora secondo Per Fisica della Materia (materia TAC ad alta risoluzione spaziale per tradizione, a premiare le Migliori condensata, atomi, molecole e piccoli animali.” Comunicazioni fatte al Congresso plasmi), primo premio ex aequo: a Nazionale della Società Italiana di Cristina Crupi del Dipartimento di Per la sezione di Fisica Applicata, primo Fisica dell’anno scorso, a Pisa, dai nostri Fisica dell’Università di Messina, per premio al Dr. Enrico Maccioni del migliori giovani, dai nostri talenti. “Thermal conductivity and low-energy Dipartimento di Fisica dell’Università Quest’anno, si tratta di una novità, i vibrational dynamics in alkali borate di Pisa, del CNISM di Pisa e dell’INFN, premi sono congiuntamente offerti da glasses”, e al Dr. Fabio Corrente Sezione di Pisa, per: “Fiber laser strain Il Nuovo Cimento, la rivista scientifica dell’INFN, Laboratori Nazionali di sensor device.” Secondo premio al propria della SIF, e da European Physical Frascati, e del Dipartimento di Metodi Dr. Aldo Mozzanica dell’Università Journal (EPJ), il giornale che la SIF e Modelli Matematici per le Scienze di Brescia e dell’INFN, Sezione di pubblica con altri partner europei. Applicate dell’Università di Roma “La Pavia, per “FAST: un rivelatore a fibre Ci sono varie sezioni tematiche nel Sapienza”, per “Polarizzazione delle scintillanti per la misura di sezione Congresso e cercherò di andare correnti di spin in nanostrutture a bassa d’urto di antiprotoni presso l’Antiproton rapidamente. dimensionalità.” Decelerator.” Secondo premio ex aequo: alla Dr.ssa Per la sezione di Fisica Nucleare e Lavinia Vaccaro del Dipartimento Per la sezione di Fisica per i Beni Subnucleare abbiamo un primo premio di Scienze Fisiche e Astronomiche Culturali, primo premio al Dr. Gianluca ex aequo: alla Dr.ssa Angela Papa dell’Università di Palermo e dell’Istituto Quarta del CEDAD, Dipartimento dell’INFN, Sezione di Pisa, per la sua di Biofisica del CNR di Palermo, per di Ingegneria dell’Innovazione, comunicazione su “L’acceleratore CW “Luminescenza risolta in tempo del non Università del Salento, Lecce, per “Il ed i metodi di calibrazione e controllo bridging oxygen hole center in silice: contributo delle tecniche di ion beam dell’esperimento MEG”, e al Dr. Said proprietà di volume e di superficie”, analysis e spettrometria di massa con Hasan dell’Università dell’Insubria, e al Dr. Stefano Bigotta dell’INFN, acceleratore del CEDAD allo studio di per lo “Studio delle proprietà di cristalli Sezione di Pisa, e della Scuola Normale contesti archeologici del Mediterraneo.” incurvati finalizzato ad applicazioni Superiore di Pisa, per “Laser cooling of Secondo premio alla Dr.ssa Giulia Festa in fisica delle alte energie”. Secondo solids: new results with fluoride single dell’Università di Roma “Tor Vergata”, per premio ex aequo: alla Dr.ssa Laura crystals.” “Study of cultural heritage artefacts by Sperandio dell’INFN, Laboratori neutron tecniques.” Nazionali di Frascati, per “The VIP Per Geofisica e Fisica dell’Ambiente, experiment (Violation of the Pauli primo premio al Dr. Mauro Mazzola Per Fisica Generale, Didattica e Exclusion Principle): new experimental dell’ISAC-CNR di Bologna, per “Effetti Storia della Fisica, primo premio limit on the Pauli Exclusion Principle radiativi diretti degli aerosol sull’area alla Dr.ssa Alessandra Mossenta violation by electrons”, e al Dr. Pier Luigi mediterranea.” Secondo premio al dell’Unità di Ricerca per la Didattica Catastini del Dipartimento di Fisica Dr. Pasquale Sellitto dell’Earth della Fisica dell’Università di Udine, dell’Università di Siena e dell’INFN, Observation Laboratory-DISP per “La costruzione di un quadro Sezione di Pisa, per “The GigaFitter for dell’Università di Roma “Tor Vergata”, interpretativo coerente delle interazioni fast track fitting based on FPGA DSP per “Algoritmi di rete neurale per elettrostatiche in un contesto di arrays.” l’inversione del dato satellitare.” formazione insegnanti.” Secondo premio alla Dr.ssa Sabrina Rossi del Per Astrofisica e Fisica Cosmica, primo Per Biofisica e Fisica Medica: primo Dipartimento di Scienze Umane per la premio al Dr. Sergio Cristallo premio alla Dr.ssa Anna Chiara De Formazione dell’Università di Milano- dell’INAF, Osservatorio Astrofisico Luca del Dipartimento di Scienze Bicocca, per “`La luna e le sue fasi´ nella di Teramo, per “Evolution and Fisiche dell’Università di Napoli scuola di base”. nucleosynthesis in low mass asymptotic “Federico II” e del CNISM di Napoli, per

68 < il nuovo saggiatore Tutti questi giovani oltre al premio Passiamo quindi a un premio che viene parecchie, è quella del premio intitolato hanno ottenuto anche la dignità dato ogni anno in ricordo di Pietro Bassi, a Giuseppe (Beppo) Occhialini. Qui di stampa per pubblicare le loro per la Fisica Nucleare fondamentale. non consegneremo il premio ma comunicazioni su Il Nuovo Cimento. “Per la sua attività sperimentale nel semplicemente proclameremo il campo della fisica nucleare e, in vincitore. Infatti questo premio è stato Adesso passerei ai giovani laureati particolare, per la rilevanza dei suoi congiuntamente istituito dalla Società cui viene conferito il premio di studi sulla multiframmentazione, sul di Fisica Britannica (Institute of Physics, “operosità scientifica” della SIF. decadimento in di-protone dei livelli IOP) e dalla Società Italiana di Fisica nel A partire da quest’anno i premi saranno eccitati del Neon 18 e sulla produzione 2007, in occasione del centenario della intitolati ai miei illustri predecessori, che di fasci di nuclei radioattivi”, il Premio nascita di Occhialini. Lo scopo è quello si sono avvicendati alla Presidenza “Pietro Bassi” 2008 è assegnato al di commemorare la figura di questo della SIF. Dr. Marzio De Napoli dell’Università di insigne scienziato, che è stato anche Il premio per i giovani laureati dopo il Catania. a Genova per un certo periodo della maggio 2005 è stato attribuito a quattro sua vita, e consolidare le relazioni tra le giovani promettenti, selezionati dal Altra novità di quest’anno, è il premio due società. Il premio è annuale e verrà Consiglio della SIF sulla base del loro intitolato a Ettore Pancini, istituito alternativamente conferito da una delle curriculum scientifico. per ricerche sperimentali in Fisica due società a un fisico selezionato a Il primo premio, non in ordine di priorità Nucleare o Subnucleare. Il vincitore partire da una lista di candidati proposti ma il primo che oggi assegniamo, è il di questo premio è stato scelto da dall’altra. Sembra un po’ complicato, Premio “Gilberto Bernardini”, che è stato una commissione esterna alla SIF, ma è semplice in realtà. Quest’anno il attribuito al Dr. Antonio Benedetto, nominata dal Consiglio della SIF. Il vincitore è stato scelto dall’IOP. laureato in Fisica presso l’Università di Premio “Ettore Pancini” 2008 I would like to ask Dr Kirby-Harris, Messina. è stato attribuito alla Dr.ssa Gilda Chief Executive of IOP, to announce Il Premio “Giovanni Polvani” è stato Scioli dell’Università di Bologna e the winner of the 2008 “Giuseppe assegnato alla Dr.ssa Chiara D’Errico, dell’INFN, Sezione di Bologna, “per aver Occhialini” Prize. laureata in Fisica presso l’Università adempiuto con originalità e successo di Firenze. (In questo momento le responsabilità affidatele dalla R. Kirby-Harris: Ladies and Gentlemen non è presente, avrà forse avuto un Collaborazione ALICE per la realizzazione, I’m very pleased to be with you here contrattempo.) l’installazione e il collaudo del sistema di today at the opening of the National Il Premio “Carlo Castagnoli” è stato misura del tempo di volo, componente Congress of the Italian Physical Society. assegnato al Dr. Giuseppe Gabriele essenziale dell’esperimento, pronto ad I’m representing our President Peter Rapisarda, laureato in Fisica presso entrare in funzione al nuovo collisore Saraga and President-Elect Dame l’Università di Catania. LHC”. Consegna il premio il Dr. Roberto Jocelyn Bell Burnell who send the best Il Premio “Augusto Righi” è stato Mazzola del CNR di Napoli, che è lo wishes to you for a successful congress. assegnato al Dr. Jacopo Parravicini, sponsor di questo premio. The Institute of Physics is delighted laureato in Fisica presso l’Università di to be a partner in the establishment Milano. Consueto premio della SIF è invece of this joint prize between our two il Premio per la Didattica o la societies and also named in honor of I premi di operosità scientifica assegnati Storia della Fisica. Quest’anno il an outstanding Italian physicist who ai laureati in fisica appena un po’ meno premio è stato assegnato per la Storia had very close working relations with giovani, cioè dopo il maggio 2001, sono della Fisica: “per il volume dedicato British physicists. The winner of the i seguenti. agli aspetti scientifici e alla attività 2008 “Giuseppe Occhialini” Prize has Il Premio “Orso Mario Corbino” va al accademica di Ettore Majorana” been selected by the Award Committee Dr. Francesco Nozzoli, laureato in (pubblicato dalle Edizioni della Scuola of the Institute of Physics from a list of Fisica presso l’Università di Roma “Tor Normale Superiore di Pisa), ex aequo nominees submitted by the Council of Vergata”. al Prof. Francesco Guerra del the Italian Physical Society. The winner Il Premio “Antonio Garbasso” va alla Dipartimento di Fisica dell’Università di is Dr. Francesco Vissani of the Gran Dr.ssa Stefania Bufalino, laureata in Roma “La Sapienza” e alla Prof.ssa Nadia Sasso Laboratory of INFN - Italy with the Fisica presso l’Università di Torino. Robotti del Dipartimento di Fisica following citation: “for his distinguished Il Premio “Vito Volterra” è conferito al Dr. dell’Università di Genova. contributions to neutrino physics and, Giuseppe Vallone, laureato in Fisica in particular, to the phenomenology presso l’Università di Torino. Ulteriore novità, quest’anno sono and theory of neutrino mass and

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Da sinistra: L. Cifarelli, F. Vissani (vincitore del Premio Occhialini) e Da sinistra: L. Pietronero, G. Casati e L. Luigiato (vincitori del Premio R. Kirby-Harris. Fermi).

mixing”. The “Occhialini” Prize and presieduta dal Presidente della Società G. Casati: Ringrazio il consiglio della SIF, Medal will be presented to Dr. Vissani Italiana di Fisica. in particolare la Presidenza, per questo at a special dinner of the Council of Per il 2008 il Premio “Enrico Fermi” premio che mi onora moltissimo. the Institute of Physics on the 27th of della Società Italiana di Fisica è stato Desidero solo proporre qualche breve November 2008. Thank you. assegnato congiuntamente ai Professori commento che riguarda anche la Giulio Casati, Luigi Lugiato e Luciano mia ricerca ma che ritengo abbia un L. Cifarelli: Last but not least, veniamo Pietronero, “per i loro fondamentali interesse più generale e mi riferisco in al Premio “Enrico Fermi” 2008 della risultati teorici nello studio dei sistemi particolare ai giovani. Società Italiana di Fisica. Si tratta del complessi”. - Questo premio è per me motivo premio più importante e prestigioso In particolare: particolare di soddisfazione in quanto della nostra Società, istituito nel 2001 in rappresenta un riconoscimento occasione del centenario della nascita al Prof. Giulio Casati dell’Università della validità della decisione presa di Enrico Fermi. Vorrei anche ricordare dell’Insubria, “per la comprensione del nei primi anni ‘70, di dedicarmi allo che quest’anno ricorre il settantesimo rapporto tra caos classico e quantistico studio dei fenomeni non lineari. Era anniversario dell’attribuzione del anche in relazione al quantum un argomento del quale nessuno si Premio Nobel a Enrico Fermi. In questa computing”; occupava, considerato privo di reale occasione la Società Italiana di Fisica ha interesse e marginale. Come potete ristampato, come primo fascicolo del al Prof. Luigi Lugiato dell’Università immaginare questa realtà mi è costata 2008 de La Rivista del Nuovo Cimento, le dell’Insubria, “per la scoperta di fatica, qualche frustrazione e un po’ di ultime lezioni di Enrico Fermi tenute qui strutture spaziali da instabilità nelle sofferenza per l’isolamento scientifico. in Italia, alla Scuola di Varenna. interazioni non lineari luce-materia”; Devo ammettere che l’enorme sviluppo Il Premio “Enrico Fermi” è destinato a un successivo ha sorpreso anche me oltre Socio della Società Italiana di Fisica che al Prof. Luciano Pietronero che rallegrato: lo studio dei fenomeni abbia particolarmente onorato la Fisica dell’Università di Roma “La Sapienza”, non lineari aveva portato alla scoperta Italiana con le sue scoperte. Il premio “per la dimostrazione dell’insorgere di fenomeni nuovi ed affascinanti viene attribuito da una Commissione di strutture frattali in una varietà quali il caos deterministico, i frattali, costituita da un rappresentante di fenomeni regolati da auto- gli attrattori strani ecc. Un numero dell’Accademia Nazionale dei Lincei, del organizzazione”. crescente di campi veniva interessato da Consiglio Nazionale delle Ricerche CNR, questa linea di ricerca che ha richiamato dell’Istituto Nazionale di Fisica Nucleare Diploma e medaglia vengono ora l’attenzione di un numero crescente INFN, del Dipartimento Materiali e consegnati ai vincitori. Li pregherei di fisici. Non solo, gradualmente un Dispositivi del CNR (cioè dell’ex Istituto a turno di intervenire con una breve po’ tutte le discipline dalla psicologia Nazionale di Fisica della Materia INFM), relazione. In ordine alfabetico, chiamo il all’economia, dall’ingegneria alla da un rappresentante del Consiglio Prof. Giulio Casati. medicina sono state interessate dalle della Società Italiana di Fisica, ed è manifestazioni del caos deterministico.

70 < il nuovo saggiatore Vorrei far notare che questo è un analogo afferma che da antecedenti porta il nome di Enrico Fermi, del quale altro esempio della importanza della simili seguono conseguenze simili. Ma egli stesso fu allievo. cosidetta “Curiosity driven research”: qui siamo passati dalla uguaglianza la ricerca non dovrebbe essere solo alla somiglianza, dalla precisione La morfogenesi, o formazione orientata a raggiungere obiettivi assoluta alla approssimazione più o spontanea di strutture spaziali a preliminarmente stabiliti. Nessuna meno buona. Esistono alcune classi di partire da uno stato omogeneo, è Nazione aveva un programma, agli fenomeni per i quali un errore piccolo uno degli argomenti più affascinanti inizi degli anni `70, di sostegno allo nei dati produce solo un errore piccolo ed interdisciplinari della scienza. In studio dei fenomeni non lineari. Il mio nei risultati. Il corso degli eventi in presenza di una instabilità spaziale interesse si è poi rivolto in particolare questi casi è stabile. Esistono altre classi una piccola modulazione iniziale, alle manifestazioni del caos in di fenomeni, più complessi, nei quali casualmente presente in un sistema meccanica quantistica, all’intersezione possono nascere casi di instabilità; il nonlineare, cresce spontaneamente di due grandi rivoluzioni del secolo numero di tali casi aumenta in modo e forma la struttura. Incontriamo scorso: la meccanica quantistica e il estremamente rapido con l’aumentare questo tipo di fenomeni per esempio caos deterministico. Il lavoro in questo del numero delle variabili. In questi in fluidodinamica o nelle reazioni campo, nuovo, sino allora inesplorato, casi, influenze la cui grandezza fisica chimiche nonlineari o, naturalmente, ha permesso di ottenere risultati di è troppo piccola per essere tenuta in negli organismi viventi. un certo interesse che poi, grazie al considerazione da un essere finito, Verso la metà degli anni ottanta il progresso nella tecnica sperimentale, possono produrre effetti della più campo in cui principalmente lavoravo, hanno ottenuto verifiche in laboratorio grande importanza. Se, perciò, quegli l’ottica moderna, era stato già oggetto sopratutto nel campo della fisica studiosi delle scienze fisiche da cui di vaste ricerche dal punto di vista della atomica e dello stato solido. il pubblico intelligente trae e forma dinamica nonlineare, ma sempre nel - Un’altra osservazione che vorrei la propria concezione… sono rivolti, dominio del tempo. In modo spontaneo fare è che lo sviluppo del sapere nel perseguire gli arcani della scienza, mi venne quindi l’idea di investigare scientifico costringe spesso ad una allo studio delle singolarità e delle la possibilità di ottenere la formazione specializzazione spinta se si vuole instabilità invece che della continuità spontanea di strutture spaziali in ottica. contribuire all’avanzamento della e stabilità delle cose, la promozione Queste strutture di luce, o patterns conoscenza. Lo studio del caos della conoscenza naturale può tendere ottici, si formano quando un fascio laser deterministico mostra invece un aspetto a rimuovere quel pregiudizio in favore di sezione grande interagisce con un opposto: gli stessi metodi si applicano del determinismo che sembra derivare mezzo materiale; la nonlinearità sorge ad un numero estremamente vario di dall’assumere che la fisica del futuro sia dalla interazione fondamentale tra luce fenomeni. Questo riflette il carattere semplicemente una immagine ingrandita e materia. di universalità di alcuni fenomeni fisici di quella del passato.” Grazie. ma anche sociali economici ecc. Questo Il mio progetto era di formulare un carattere di universalità è un aspetto L. Cifarelli: Grazie. Chiamo adesso il modello che prevedesse questo importante che deve essere motivo di Prof. Luigi Lugiato. fenomeno ed avesse lo stesso grado riflessione. di relativa semplicità dei modelli - Infine chiudo il mio intervento con un L. Lugiato: Desidero ringraziare molto prototipici che descrivono le reazioni pensiero che ha ispirato la mia ricerca, la Presidente Cifarelli e la Società chimiche nonlineari in 2D. La difficoltà ed è di un grande genio della fisica, Italiana di Fisica per questo Premio, che principale risiedeva nel fatto che James Clerk Maxwell che, con una sono veramente onorato di ricevere con nel caso dell’ottica, oltre alle due straordinaria intuizione, in anticipo di gli stimati colleghi ed amici Giulio Casati dimensioni della sezione del fascio vi oltre un secolo, aveva colto l’essenza di e Luciano Pietronero. è una terza dimensione in cui il fascio questi fenomeni. Nel 1873 scriveva: Desidero dedicare questo si propaga, e questa circostanza rende “È una dottrina metafisica che dagli riconoscimento prima di tutto a mia molto più complesso modellizare tali stessi antecedenti seguono le stesse moglie Vilma, che ha sostenuto e fenomeni. Per poter trascurare la terza conseguenze. Nessuno può dubitare sopportato la mia vita di fisico. In dimensione si può considerare un di questo. Ma ciò non è di molta secondo luogo al compianto Piero campione di materiale molto corto, ma utilità in un mondo come il nostro Caldirola, che fu il mio principale in questa situazione l’interazione tra in cui gli stessi antecedenti non si maestro e che sarebbe orgoglioso di luce e materia è anch’essa trascurabile. verificano mai e nulla capita due vedere due suoi allievi (Giulio Casati ed Per risolvere questa difficoltà pensai di volte… L’assioma fisico di contenuto il sottoscritto) ricevere un premio che racchiudere il campione in una cavità

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ottica in modo che la luce rimbalzasse essere anche spostati e/o messi in moto cosa ringrazio il Presidente Luisa Cifarelli moltissime volte tra i due specchi della in maniera controllata e tutte queste e la Società Italiana di Fisica per questo cavità prima di uscirne ed in tal modo proprietà sono molto interessanti nella grande onore che apprezzo veramente, interagisse in modo significativo con la prospettiva di processare informazione. sono onorato e commosso da questo materia. riconoscimento. Il modello che formulai per il campo Una seconda via applicativa è la Volevo, in questa occasione, prendere elettrico includeva i due elementi seguente. In condizioni opportune, le un attimo le distanze dalla cronaca necessari per la formazione di patterns leggi dell’ottica nonlineare fanno sì che e riguardare un po’ la mia personale spaziali, cioè la nonlinearità e la i vari elementi del pattern siano correlati storia da una certa prospettiva, quindi diffrazione, ed era equivalente ad una quantisticamente tra di loro. Questo comincio col ringraziare le persone equazione di Schroedinger nonlineare stato di entanglement spaziale è di con cui ho cominciato ad imparare con l’aggiunta di un termine forzante interesse nel campo dell’informazione la fisica che sono nell’ordine Bruno che descrive la luce entrante in cavità quantistica. In particolare, questo ha Touschek, che ricordo con grandissimo e di un termine di smorzamento che contribuito alla nascita di una nuova affetto e stima, e Franco Bassani a cui descrive la luce uscente dalla cavità . disciplina, denominata Quantum vorrei inviare un caro saluto. Sapete Verificai che l’equazione prevedeva Imaging, che sfrutta la natura Franco è piuttosto malato, l’ho visitato la presenza di una instabilità spaziale quantistica della luce e l’intrinseco pochi giorni fa e l’ho trovato di buono e Renè Lefever dimostro che questa parallelismo dei segnali ottici per spirito quindi colgo questa occasione portava effettivamente alla formazione inventare nuove tecniche per fare per ringraziarlo e fargli i miei migliori di strutture spaziali. imaging e per processare l’informazione auguri. Questo risultato inaugurò un nuovo in parallelo a livello quantistico. Io, devo dire, ho una storia un po’ campo che venne denominato Optical Per esempio, per determinare gli strana perché mi sono laureato a Roma, Pattern Formation e fu oggetto di molte spostamenti di un oggetto con una quindi sono un prodotto del sistema indagini anche sperimentali, tra le quali precisione che sorpassa il limite italiano, e quindi anche della Società si segnalano quelle del gruppo di Tito quantistico standard. Italiana di Fisica in senso lato, però Arecchi, che ha ricevuto questo Premio dal giorno dopo la laurea sono stato due anni fa. Poiché questo congresso si svolge nella all’estero per 16 o 17 anni e non ho città di Genova, desidero ricordare mai lavorato in Italia finché non sono Nell’ambito della morfogenesi, il che Genova è la sede dell’Istituto tornato verso la fine degli anni `80. vantaggio dell’ottica è che i sistemi Nazionale per la Fisica della Materia Quindi in questo senso sono un vero ottici rispondono su scale di tempo ( INFM) che è stato incorporato nel straniero, perché quando sono tornato veloci e possono trasmettere su Consiglio Nazionale delle Ricerche. In non sapevo proprio nulla dell’Italia e, una larga banda di frequenze, il che questa operazione la rete universitaria, a parte la lingua e pochi ricordi liceali, permette prospettive di applicazione, che costituiva l’ossatura e l’anima è stato un impatto notevole. Devo ed a questo proposito vorrei ringraziare dell’INFM, è rimasta tagliata fuori. dire che, tutto sommato, l’educazione soprattutto i colleghi Massimo Spero che non sia utopistico auspicare scientifica che ho avuto è stata buona Brambilla, Franco Prati ed Alessandra che l’INFM possa tornare ad essere nonostante fosse iniziata nel `68, Gatti per la loro preziosa collaborazione indipendente, con una configurazione quindi in un periodo estremamente su questi temi. ed un finanziamento paragonabili a turbolento. Direi però che le strutture Una prima via applicativa è quella quelli dell’epoca pre-CNR. E, più in erano solide e non mi sono mai sentito dei cosiddetti solitoni di cavità. generale, auspico che il mondo politico di avere un handicap nel confrontarmi Tipicamente, gli elementi di un pattern prenda coscienza del fatto che ricerca con le istituzioni straniere, in cui spaziale sono fortemente correlati tra di scientifica e formazione universitaria pure fui apprezzato. Questo mi pare loro: se, per esempio, si genera un solo non sono solo una sorgente di spesa per un elemento molto importante e elemento, questo crea spontaneamente lo Stato, ma rappresentano soprattutto dobbiamo cercare di mantenerlo e di l’intero pattern. Tuttavia, in condizioni una risorsa fondamentale per il futuro valorizzarlo, cioè non è vero che le cose speciali gli elementi diventano del nostro Paese. Vi ringrazio. sono così negative tutto sommato, realmente indipendenti e si può almeno nel mio caso è stata una buona avere anche un solo elemento isolato. L. Cifarelli: Chiamo infine il Prof. educazione, gratuita, con persone Questi “solitoni di cavità” possono Luciano Pietronero. di primissimo livello. Io sono stato essere scritti in posizioni a piacere e molti anni nell’industria, la Xerox e la poi cancellati singolarmente. Possono L. Pietronero: Buongiorno, per prima Brown Boveri di Zurigo e poi diventai

72 < il nuovo saggiatore professore universitario in Olanda. un’area di due campi da tennis, quindi menzionavo. Concludo ringraziando Tornato in Italia la cosa è stata molto la fisiologia ha ripiegato nel nostro voi tutti e facendovi i migliori auguri diversa perché ero dall’altra parte del torace una struttura complicatissima per un’attività gradevole e di successo. tavolo rispetto al periodo studentesco, che è funzionale a scambiare molto Grazie e buona giornata. cioè ero parte del sistema che doveva ossigeno in pochi secondi. Potremmo produrre la ricerca e l’insegnamento, e fare molti altri esempi, non vi annoio L. Cifarelli: Siccome Luciano Pietronero naturalmente non ci si annoia in Italia, con una descrizione tecnica, se vi ha parlato dei giovani, spero che siate si combatte tutti i giorni, però tutto interessa c’è la pagina web o un libretto tutti d’accordo se, facendo una piccola sommato per me il punto chiave per dell’Editore Di Renzo (http://www. infrazione al cerimoniale, premiamo cui il mio gruppo è funzionato sono direnzo.it/) dove queste cose sono lo stesso e in extremis una giovane stati degli ottimi studenti. Quindi io esposte in modo divulgativo. Volevo ritardataria. Il Premio “Giovanni Polvani” ringrazio sia le persone che mi hanno fare ancora un commento di carattere di operosità scientifica, per laureati insegnato le cose, ma anche quelle generale, come dicevo le attività del dopo il maggio 2005, viene dunque che hanno collaborato con me e che mio periodo italiano sono andate consegnato anche alla Dr.ssa Chiara per me la chiave del fatto che la nostra molto bene grazie ai giovani e brillanti D’Errico, laureata in Fisica presso attività è funzionata bene anche in collaboratori che ci sono stati sempre l’Università di Firenze. Italia. Naturalmente il confronto con e ci sono tuttora e questo credo sia Infine, in conclusione di questa l’estero ci deve far riflettere e dobbiamo un valore grandissimo che va sempre Cerimonia di Premiazione del valorizzare i nostri punti migliori e più valorizzato. Purtroppo vedo delle Congresso, vorrei annunciare che cercare di diminuire i difetti. In Italia ci carriere sempre più frustrate dei nostri tra i Soci Benemeriti 2008 la Società sono delle eccellenze spesso circoscritte brillanti giovani, questo è un grande Italiana di Fisica non poteva mancare nell’ambito di un piccolo gruppo e danno e dobbiamo creare delle carriere di nominare il Prof. Giuseppe-Franco ci sono carenze nella creazione di brillanti come io ho avuto la fortuna di Bassani, mio predecessore alla strutture abbastanza grandi a livello avere. Quindi io mi faccio promotore Presidenza della Società, Fellow della nazionale. Anche la SIF credo che si dell’iniziativa che per quanto possibile European Physical Society e di altre renda conto di queste difficoltà che dobbiamo cercare di valorizzare i nostri società scientifiche, adesso Presidente dobbiamo cercare di superare. giovani e dare le opportunità che tanti Onorario della SIF. Bassani non ha Dal punto di vista scientifico la nostra di noi abbiamo avuto fortunatamente, potuto essere oggi con noi, ma lo vedrò principale attività corrisponde alla anche se all’epoca non sembrava che a Pisa tra una quindicina di giorni per domanda perché la natura genera la situazione fosse così buona, ma un incontro di lavoro e gli consegnerò delle strutture complesse, le strutture certo che in retrospettiva bisogna personalmente diploma e medaglia.(*) complesse sono davanti a noi da dire che lo era. L’altra cosa poi è il Passo ora a una mia breve relazione di sempre, però la domanda scientifica passaggio da attività di gruppi singoli, apertura. invece è solo da vent’anni che ce la che ce ne sono tantissime in Italia, a poniamo, il motivo è che mancava attività più strutturate. Questo è un Innanzitutto sono molto lieta che proprio la tecnologia concettuale passaggio difficile. Ma io credo che se la Società Italiana di Fisica abbia per porsi queste domande. Queste vogliamo lavorare a un livello nazionale, organizzato il suo Congresso a domande io me le sono poste confrontarci con l’Europa, col mondo, Genova, in collaborazione con il DIFI mentre facevo altre cose, discutendo confrontarci anche con l’industria (Dipartimento di Fisica dell’Università). casualmente con altri, quindi sono italiana e le aziende, è importante che È la terza volta che il Congresso della venute come una componente laterale le cose abbiano anche una struttura SIF si svolge a Genova, la prima volta dell’attività che però man mano poi di una certa dimensione. Per questo fu quasi un secolo fa nel lontano 1912, ha preso il sopravvento ed è diventata motivo già anni fa insieme a vari la seconda nel 1984 e infine la terza in qualche modo quella principale. colleghi cercammo di fondare l’Istituto quest’anno, e siamo onoratissimi di Questo è stato un percorso abbastanza dei Sistemi Complessi del CNR, che fu essere di nuovo qui. Tra l’altro vorrei lungo con domande diverse, questioni fondato nel 2004, è vivacchiato per 2 o 3 menzionare che ricorre quest’anno diverse, il punto essenziale era di anni nei periodi particolarmente difficili il 25° anniversario della costruzione capire “come mai la natura invece di e adesso è stato stabilizzato giusto scegliere una struttura semplice ne poche settimane fa. Quindi mi auguro, sceglie una estremamente complessa?”. per questa opportunità che ci viene (*) G.F. Bassani è purtroppo venuto a mancare Possiamo vedere che la fisiologia concessa, di poter dare un contributo pochi giorni dopo l’inaugurazione del è già così, i nostri polmoni hanno a questi problemi che appunto Congresso, il 25 Settembre 2008.

vol24 / no5-6 / anno2008 > 73 del complesso del Dipartimento di terrà nel pomeriggio del 25 settembre, poche settimane di riparazione. Per una Fisica dove si svolgeranno i lavori ne sarà il moderatore il Prof. Antonino macchina tecnologicamente “estrema” del Congresso, a partire da oggi Zichichi, che è qui presente, e avremo come LHC, occorrerà un fattore dieci pomeriggio. Sono stati ricordati l’onore della presenza del Ministro di tempo in più. Dovremo quindi alcuni illustri fisici che hanno lasciato Claudio Scajola. L’interesse e le attività pazientare ancora qualche mese per la loro impronta a Genova, come della SIF per l’energia nascono un anno l’avvio definitivo di un progetto che ci Beppo Occhialini, cui si devono grandi fa da un’iniziativa europea, coordinata riserva tante promesse. scoperte con i raggi cosmici. Occhialini dalla Società Europea di Fisica Su questo grandioso progetto sono è stato a Genova dal 1949 al 1951, (European Physical Society, EPS), di cui state dette e scritte molte cose. Vorrei contribuendo a esperimenti di lancio tornerò a parlare tra un attimo. invitarvi a leggere un interessante di emulsioni tramite palloni aerostatici. Non potevo inaugurare questo articolo scritto da Leon Lederman Di Ettore Pancini abbiamo parlato, Congresso senza soffermarmi sul Newsweek del 16 Settembre (dal tutti noi lo ricordiamo per il famoso sull’evento epocale già menzionato titolo “What we’ll find inside the atom”), esperimento, realizzato insieme a dal Prof. Enzo Boschi, cioè l’inizio di in cui esordisce ponendo al centro Oreste Piccioni e Marcello Conversi, per LHC. Il comunicato stampa emanato dell’attenzione la figura di Galileo la scoperta del muone: anche lui è stato il 10 settembre dal CERN annuncia il Galilei e il suo ingegnoso e potente a Genova, dal 1952 al 1960. Infine vorrei completamento della macchina e i telescopio che permise di realizzare menzionare Antonio Borsellino, cui si primissimi test di circolazione devono i grandi passi della biofisica a di fasci di protoni al suo Genova e in Italia nei primi anni `60. interno. Nella nota fotografia Nel Dipartimento di Fisica la Biblioteca del tunnel di LEP, adesso è intitolata a Borsellino, a Pancini l’Aula di LHC, si vedono i dipoli Magna. Quest’anno sarà intitolata a superconduttori che Beppo Occhialini un’altra grande aula. funzionano in criogenia, ce Infine segnalo che al Dipartimento è ne sono più di mille lungo i allestita una mostra poster, che sarà 27 km di circonferenza del visibile durante tutto il Congresso, su tunnel, sono lunghi circa 14 questi importanti personaggi della fisica metri ciascuno e funzionano italiana. a meno di 2 gradi Kelvin Il Congresso è ricchissimo di eventi: ci in un bagno di elio liquido sono 8 Sessioni Parallele, 13 Relazioni superfluido. Plenarie, ci sarà una Conferenza Durante la recentissima fase Cittadina (o, addirittura, un intero di collaudo di LHC, nel portare “pomeriggio cittadino”), e una Tavola un gruppo di questi dipoli Rotonda sul tema dell’energia in Italia. in regime di alta corrente, L’Assemblea Generale dei Soci, dove si è verificata una scarica svolgerò la consueta Relazione del che ha provocato un guasto Presidente su questioni propriamente meccanico e la fuoriuscita societarie, sarà il 23 settembre e la Cena di una certa quantità di elio Sociale, altro significativo momento di liquido in un settore del incontro tra i Soci, il 24 settembre. La tunnel. In una macchina Tavola Rotonda sull’energia in Italia si convenzionale occorrerebbero

74 < il nuovo saggiatore in passato spettacolari scoperte, così e si chiamano “yellow report”) sulle squadra, in un sottogruppo di lavoro come ci aspettiamo di fare oggi grazie origini di LEP e LHC [CERN/DG-2004- dedicato ai rivelatori di particelle. La a LHC. Vi invito anche a leggere una 306/0]. È stato pubblicato in onore di copertina del White Book, che riporta recente intervista di Lederman al Antonino Zichichi e ritengo doveroso il tracciato del LEP, è qui mostrata Corriere della Sera, in cui ricorda Enrico parlarne, sia pure molto brevemente, in insieme a una fotografia aerea della Fermi come precursore di LHC, poiché questa occasione. zona rappresentata dall’antica mappa capì in anteprima l’importanza degli Il rapporto giallo contiene la in bianco e nero. Si tratta dei dintorni acceleratori di particelle e in particolare riproduzione integrale di quello che di Ginevra. In sovraimpressione sulla della fisica adronica, proprio la fisica è noto come “ECFA-LEP White Book”, fotografia compare l’effettivo tracciato che andremo a esplorare con questo un rapporto che fu redatto alla fine di LEP, ora LHC. In basso, sulla mappa e prodigioso strumento che è LHC. degli anni ’70 quando la Commissione nella foto, si vede un piccolo triangolo Tuttavia vorrei aggiungere ancora Europea per i Futuri Acceleratori (ECFA) che è proprio il CERN. Il White Book è qualcosa a proposito di LHC. incaricò Zichichi di formare un gruppo una preziosa testimonianza su come Per il cinquantesimo anniversario di lavoro allo scopo di dirimere la LEP sia stato ideato per essere poi del CERN, celebrato nel 2004, è stato questione di dove fare una macchina costruito al CERN. pubblicato un rapporto (al CERN i e+e– e come farla. Circa 350 fisici si A pagina 304 del White Book si può rapporti scientifici sono di colore giallo misero all’opera. Anch’io feci parte della leggere qualcosa di interessante che

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riporto fedelmente: “It was noted that pesanti a energie mai finora raggiunte. Society (EPS). We are celebrating the the choice of cross-section of the LEP main In definitiva, è giusto dire che LHC è 40th anniversary of the Society. I would tunnel takes into account the possibility of il risultato della visione di un ristretto like to thank Prof. Maciej Kolwas, adding a proton machine later if needed. numero di persone illuminate e del President-Elect of the European Physical This was considered of great importance. formidabile sforzo, nell’arco di più di Society, Member of the Polish Academy It was even felt that a slight increase of the due decadi, di una grande comunità of Sciences in Warsaw, for his presence tunnel cross-section might be advisable internazionale di fisici e tecnici, tra i here, together with Dr David Lee, and in any case provision should be quali ovviamente Luciano Maiani, già Secretary General of EPS, and other made for accomodating the cryogenic Direttore Generale del CERN. Council Members of EPS, in particular: equipement required for superconducting Per concludere, poiché sono uno Dr Robert Kirby-Harris, Chief Executive magnets.” Quindi già nel 1979 il gruppo dei tanti fisici che collaborano of IOP, Dr Caterina Biscari of INFN- di lavoro ECFA-LEP guidato da Zichichi all’esperimento ALICE di LHC, Frascati, Head of the Accelerator Group aveva pensato, come riconosciuto permettemi di mostrare la ricostruzione of EPS, and Prof. Marcello Giorgi of the pubblicamente in passato anche dal di un evento registrato la notte dell’11 University of Pisa, INFN Representative Prof. Luciano Maiani che è qui presente settembre nel rivelatore al silicio ITS, la in the EPS Council. Let me acknowledge e che saluto molto cordialmente, di parte più interna del nostro apparato as well the presence Prof. Renato scavare un tunnel circolare del giusto sperimentale. Si tratta della collisione Angelo Ricci, Past President of EPS perimetro e soprattutto di farlo con una di uno dei primi protoni circolanti a (1988-1991). sezione trasversa sufficientemente larga LHC contro un nucleo, probabilmente The celebrative Plenary Talk will be da poter semmai ospitare in futuro, presente nel gas residuo del tubo a given by Prof. Antonino Zichichi, also dopo una macchina e+e–, una nuova vuoto della macchina. Quindi, come Past President of EPS (1978-1980), macchina adronica. vedete, il fascio c’era e gli esperimenti moreover the youngest signer of the Così è stato. LEP ha funzionato dal funzionavano. Siamo tutti pronti per la EPS foundation chart in Geneva, 40 1989 al 2000 in un intervallo di grande avventura. years ago. This anniversary is indeed energia tra 100 e 200 GeV, anzi un pò A questo punto dichiaro ufficialmente an occasion to recall the birth of oltre i 200 GeV, e grazie all’adeguato aperto il XCIV Congresso Nazionale the European Physical Society and diametro della sua sezione ha potuto della Società Italiana di Fisica. to pay a tribute to its first President, ospitare successivamente un collider The first Plenary Talk – let me switch Gilberto Bernardini, whose remarkable superconduttore come LHC che fornirà to English – will be devoted to the engagement as a man and as a scientist interazioni sia di protoni sia di nuclei celebration of the European Physical will be duly recalled.

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THE 40TH ANNIVERSARY OF EPS: GILBERTO BERNARDINI’S CONTRIBUTIONS TO THE PHYSICS OF THE XX CENTURY(*)

Antonino Zichichi CERN, Geneva, Switzerland Enrico Fermi Centre, Rome, Italy INFN and University of Bologna, Italy

Gilberto Bernardini’s Physics

› The discovery of the µ (Conversi, Pancini, Piccioni) in Italy. › The π photoproduction in USA. › The discovery of π → β decay (V – A) at CERN.

› The QED high-precision checks outside (e–γ): (g – 2)µ (using the “flat-magnet”: 6 m long, the longest in the world with ∆B/B ≅ 10–4 polynomial field) at CERN. τ › The high-precision measurement of GF (via µ) at CERN. › The “weak magnetism”_ at CERN. › The discovery of (nm ≠ nm) at CERN. › The discovery of the J/ψ which could have been achieved in Italy, many years before Ting and Richter, as well as the discovery of the 3rd lepton, many years before Perl, if Gilberto Bernardini had been Director of Frascati Lab.

Introduction

We believe that the best way to celebrate the 40th EPS Anniversary is to illustrate the activity of its first President Gilberto Bernardini. His achievements in Physics were coupled with his remarkable engagement in Italy: • to create the first National Institute for the study of Nuclear Physics, INFN; and in Europe: • to create in the first European great new Laboratory – CERN – the scientific basis for the Lab to become first competitive with the USA Physics supremacy and than the leader in the field, as it is now; • to establish the existence of the European Physical Society – EPS.

(*) Opening Plenary Talk at the 94th National Congress of the Italian Physical Society, Genoa, Palazzo Ducale, Sala del Maggior Consiglio, 22 September 2008.

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Gilberto Bernardini’s contributions to the Physics of the XX Century can be synthetically summarized as follows:

1. His engagement to unify the Physics community in Italy and in Europe 2. His achievements as 1st CERN Research Director 3. His Physics 4. The Physics which could not have existed without his strong involvement 5. His interest in the frontiers of Physics which never declined 6. His enthusiasm as testified by Leon Lederman.

Let me start with the words of Bernardini that bring us back to the mid nineties.

How I met Him: a testimony by Gilberto Bernardini [1] In Pisa, June 12-15, 1955, there was the International Conference on Elementary Particles [2]. The hottest topic of the Conference was the properties of the “Strange particles” observed in cosmic ray experiments. A fellow from the Blackett group presented some interesting results “On the production of V particles” (page 325 of [2]). During the presentation, James wrote the following reaction:

(1) (page 328 of [2]).

The youngest collaborator of Enrico Fermi, Murray Gell-Mann, was in the audience. He pointed out that reaction (1) does not conserve "strangeness". During the discussion, a young fellow said, in very broken English, that reaction (1) could proceed via the "strangeness-conserving" channel. In fact, he added, in the experiment reported by the Blackett group, the particle θ0 had to be considered far away from the production process Fig. 1 Photo and front page from [4]. and therefore, according to a new idea of Gell- Mann himself and Pais, the θ0 particle born as a pure "strangeness-plus-one-state", soon becomes a mixture of 50% "strangeness-plus-one" and 50% "strangeness-minus-one". Reaction (1) contains therefore 50% "strangeness-minus-one" in the initial state and this produces the "strangeness- minus-one" baryon (Λ0) in the final state. It was q0 q0 the first time I had ever heard of the ( 1– 2) problem, discussed a few months before the Pisa

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Conference by M. Gell-Mann and A. Pais The work of Puppi [5], which is at the [3]. The young Italian fellow was Nino origin of the famous “Puppi Triangle” Zichichi, the latest comer to the Physics that bears his name (fig. ),2 was the first Institute in Rome, as I found out talking step towards the Universality of the to him, after the discussion session. He Weak Forces and indeed attracted the (np) was very lucky to have been sent to Pisa attention of Enrico Fermi, since it was (at the last minute he replaced a senior the first proof that all Weak processes fellow from Rome who could not attend could be described by the same the Conference). In fact, it is thanks to this coupling. event that Blackett invited Nino to join his It came just a year after the discovery group. by Marcello Conversi, Ettore Pancini and Oreste Piccioni [6] that the negative cosmic-ray “mesons” (now known to (µ, µ0) (e, ν) 1 His engagement to unify the be the leptons called muons) were Physics community in Italy and in disintegrating as if they were not Fig. 2 The Puppi Triangle, the 1st step towards Europe strongly coupled to the Nuclear Forces. the Universality of the Weak Forces.

I would like to recall here what Puppi wrote in 1968 concerning the role of 2 His achievements as 1st CERN Bernardini in the renaissance of Italian Research Director and European Physics after the World War II (fig. )1 . Scientific Europe predates Political Europe. Gilberto Bernardini: Man and Scientist Italian pioneers made a decisive – a testimony by Giampietro Puppi [4] scientific contribution to the birth Gilberto Bernardini belongs to the sparse of CERN. We should be proud of our group of teachers that we credit with the own Bruno Ferretti’s leadership of the post-war rebirth of Italian Physics and its Theoretical research at CERN, and how association with the culture and ideals of Experimental research was initiated and the Fermi and Rossi school. directed by our Gilberto Bernardini. It The phases of its recovery were: the was his scientific ideas that enabled Plateau Rosa Laboratory on Mount the nascent Laboratory to dive right Cervino, an enterprise launched by in to front-line experimental work in Bernardini in ‘47; the creation of the the incipient scientific competition National Institute of Nuclear Physics, of between Europe and the USA. which he was President from ‘54 to ‘61; Bernardini, a convinced Europeanist Italy’s participation at CERN, where he and the first President of INFN (National worked as director of the SC division from Institute of Nuclear Physics) (fig. ),3 ‘57 to ‘64, and afterwards as Research was among the CERN founding fathers Director; the construction of the Frascati who convinced governments to give synchrotron, which his enthusiastic soul the “green light”; Bernardini for Italy, and experience helped realize. Rabi for the USA, Blackett for England A man that placed his heart before reason and Bohr for Denmark and other with the firm conviction that he was doing European countries. The creation of the opposite, who professed the most CERN launched a scientific Europe scrupulous democracy with a perfectly that predated political Europe. Today, aristocratic soul; enamored of culture, it is first rank in the study of the most convinced of the truth of life, but proud to advanced scientific frontiers. pay a high premium for what culture and Thanks to Gilberto Bernardini Italy life gave him in return. played an exceptional scientific role in this new European Laboratory. The 1 Bruno Brunelli (Note added). first Scientific Director of the Physics

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Division was Gilberto Bernardini. He guided research activities towards the high-precision QED tests and to the study of the Weak Forces. It is thanks to Gilberto Bernardini that the first discovery at CERN attracted the attention of the scientific world: the discovery of theπ → β decay [7, 8]. Reason: the crux of the matter concerned a fundamental property of the Weak Forces. According to how it had been measured in the USA, something that should have happened did not. In reality, it actually did happen, ten times more than the previous experiments claimed. The discrepancy was an error of a Fig. 3 The Frascati Electron-Synchrotron in 1958, at the time when Gilberto Bernardini factor of ten. st was leading the INFN as its 1 President. Under the scientific direction of Gilberto Bernardini, a technique was invented for constructing very high-precision magnetic fields [9]. This invention allowed the first measurement of the so-called “virtual effects” in the electromagnetic properties of the particle – called muon – that was identical to the electron, but two hundred times heavier. This was no minor accomplishment. The mystery of the muon was identified by Fermi as “the price to pay for having understood almost everything.” Nature does not spend its energy uselessly. Why do leptons exist, identical to electrons in every respect except mass? The need for high-precision measurements of the “electromagnetic” identity of muons, in other words, resulted from the need to compare them with electrons. The experiment required new technologies. The most essential need was to construct powerful, high-precision polynomial magnetic fields. There had already been attempts to do Fig. 4 Gilberto Bernardini at CERN. From left: Francis Farley, A. Z., this, in both the USSR (at Dubna) and the USA. Gilberto Bernardini, Theo Muller, Hans Sens and George Charpak. It is Gilberto Bernardini decided that this was a Gilberto Bernardini who wanted the engagement of CERN in a “high precision” experiment to check the validity of the “virtual physics”, problem worth focusing on, so he encouraged whose existence – up to that time – had been put under accurate a group of young physicists to study how to experimental test using only the source of electromagnetism: the approach it (fig. ).4 This led to an invention electron. called “magnetic shimming”, which is in use everywhere today. Instead of requiring years and years to model a magnetic pole, the new technique enabled (and still enables) us to “profile” magnetic poles in just a few hours. And so it was that the longest magnet in the world (6 metres), made up of a sequence

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of high-precision magnetic fields, was constructed at CERN [9] (fig. ).5

The muon (g −2): Another testimony by Gilberto Bernardini [1] The high-precision measurement of the anomalous magnetic moment of the muon was an experiment I wanted to encourage when I joined CERN as Research Director responsible for the SC. Many ideas were proposed. Two of them were the “screw-magnet” and the “flat- magnet”. Here the problem was the complexity of the magnetic field needed: injection, ejection, storage and transition fields. According to the SC greatest magnet specialist, Dr. Bengt Hedin, many months of high precision mechanical work were needed in order to produce just one “shape” of a given polynomial field. In order to reach the final correct shape, further high precision machining was needed. The conclusion was that, in order to shape the “flat-magnet” poles in such a way as to produce the complex polynomial fields needed for the “flat-magnet”, the mechanical preparation of the magnet poles required no less than five to six years. The “screw-magnet” started to be built. Meanwhile Nino had the idea of trying a new Fig. 5 A drawing and a photo of the six-metre “flat magnet” (the biggest in the world) very simple technique: shaping a flat-pole with where a sequence of high-precision magnetic fields has been implemented using the very thin iron sheets, glued using the simplest “shimming technology” [9]. The “shimming technology” allowed the highest-precision possible method: “scotch tape”. In this way, magnetic fields to be implemented in a very short time. instead of 6 years, a few months of hard work allowed Nino to conclude that polynomial fields of practically any desired form could be built with better than 10–3 accuracy. The six-metre long magnet containing an injection field, followed by two transitions, a storage, another transition and finally an ejection field (total: 6 polynomial fields), became the core of the high-precision measurement of the muon (g − 2).

The result: for the first time ever, it was proven that the electromagnetic properties of the muons were identical (to a precision of five parts in ten thousand) to those of the electrons [9-13]. The mystery of the muon remains unsolved even today. What’s more, it has been extended to encompass the third lepton and the twelve Fig. 6 The present status of flavour states classified in terms of three families, each fundamental particles (fig. ),6 the mass values one being composed of a quark pair plus a lepton pair [14]. The experimental search for the lepton pair of the 3rd family started at CERN in the early sixties [15] of which are ad hoc “parameters” of the and moved to Frascati where the (e+e–) ADONE collider began to operate in 1967 [16-18].

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_ Fig. 7 The experimental set-up used for the discovery of nm ≠ nm. On the right, Helmut Faissner – a close collaborator of Gilberto Bernardini – with a colleague in the counting room of the experiment.

Fig. 8 Gilberto Bernardini at the end of the seventies.

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Standard Model. could appear “obvious” now – more than half a century later It will always be to Bernardini’s credit that he encouraged – we know that the π can also be, it must be, photoproduced. the first high-precision measurement of the so-called “weak” But at that time the problem of investigating the production charge, which allowed us to better understand the Weak mechanism of the π meson (now called pion) came up and Forces [19, 20]. Gilberto Bernardini was able to prove that the pion was These are also called Fermi Forces, after the greatest Galilean indeed photoproduced. We now know that the “µ meson” of the XX Century, who first advanced their mathematical is the µ lepton, as proved by Conversi, Pancini and Piccioni [6], formulation. and is the decay product of the “nuclear glue” via the chain Another discovery credited to Gilberto Bernardini is that of reaction distinguishing the muonic_ neutrino from the muonic anti- neutrino; in symbol: nm ≠ nm [21] (see also [20, 22]) (fig. ).7 The first “machine” at CERN had an energy equivalent to 600 million electron Volts. This is where the π → β [7, 8] discovery This is the discovery of Beppo Occhialini with Lattes and was achieved together with the high-precision QED tests Powell [26, 27].

(g–2)m [9-13]. After his activity in the States, Bernardini came to Geneva The next one reached 28 billion electronvolts (28 GeV) for and decided to engage the newly born European Lab – CERN protons against a fixed target. This machine_ was called PS – into the most advanced frontiers of Physics: high-precision (Proton Synchrotron). This is where nm ≠ nm was discovered checks of QED and the study of the Weak Forces. [21] (see also [20, 22]). These were times dominated by the Strong Interactions using And this is when Gilberto Bernardini left CERN (fig. ).8 the “Bubble Chamber” technology. It was not a trivial matter The next CERN great achievement was the first (pp) collider to give priority to other fields of Subnuclear Physics, such as in the world where two beams of protons of 31 GeV each QED and Weak Interactions. Here the key experiment was the were made to collide and produce a total energy of 62 GeV. search for the β decay of the π meson (fig. ).9 This machine was called ISR (Intersecting Storage Rings). The Previous experiments by Anderson [28] and by Steinberger two supermachines, SPS (Super Proton Synchrotron) and [29] had given the result that the branching ratio LEP (Large Electron Positron collider), surpassed all previous Rexp = (π→β / π→µ) was below 10–5. It was not easy to repeat levels, and the LHC (Large Hadron Collider) machine soon in such an experiment, competing with the results obtained by operation will have an energy of 14 thousand billion eV (14 distinguished fellows as those mentioned above. TeV) and, later 16 TeV. And this is where we are now. I remember a meeting in his office of Research Director in the Physics Division, where Bernardini was trying to explain to us, young fellows, the relevance of the β decay of the π meson. 3 His Physics The CERN group, led by Paul Merrison, discovered [7, 8] that the π → β decay rate was an order of magnitude higher than This consisted in the study of: the previously established limit (fig. 10), thus opening the • the negative and positive (high energy) “penetrating” way to the (V – A) theory of the Weak Forces. cosmic rays, The other great contribution of Gilberto Bernardini was to • the pion photoproduction, take as priority for CERN the field of high-energy neutrino • the (V - A) nature of the Weak Forces by means of a key Physics. experiment, Unfortunately the expected rate of the neutrino events • the muonic neutrino, with the discovery, as already was estimated by two distinguished physicists assuming mentioned, that it had its own antiparticle. all decays occurring with zero opening angle. It was Guy His contributions to the Physics before the World War II are the von Dardel who pointed out that, once this approximation studies of the “hard cosmic-ray component” with the idea to was corrected by taking into account the decay angular investigate this component using a strong magnetic field [23]. distribution of the µ-neutrinos, the expected number of This generated the great discovery by Marcello Conversi, events was an order of magnitude below. Ettore Pancini and Oreste Piccioni [6]: the “µ meson” cannot This order of magnitude error resonated with the theoretical be the “nuclear glue” suggested by Yukawa since it had no view by Léon Van Hove who was saying: “Nature cannot be so nuclear interaction. stupid to have two neutrinos, since one is enough to do what is The period after the World War II brought him to the needed.” proof that the “nuclear glue” (the π meson) could also be The result was that the neutrino Physics strongly supported produced by the electromagnetic quanta. The first proof of by Bernardini lost its priority at CERN and this is why the π photoproduction is due to Gilberto Bernardini [24, 25]. It experiment was done at BNL with the discovery [31] that two

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neutrinos νe ≠ νµ were indeed needed to make the world as it is (a detailed description of the BNL experiment can be found in [20, 22]). The next question was to establish if ν _ µ and anti-νµ, nm, were or were not the same particle. Scientific justice was finally given to Bernardini’s neutrino Physics priority. In fact it is at CERN that this discovery was achieved [21].

4 The Physics which could not have existed without his strong involvement

I have already mentioned the (g – 2)µ experiment. Let me now tell you about other relevant research lines strongly supported by Bernardini at CERN.

The Isovector-vector conserved current and Fermi couplings with DS = 0 Feynman and Gell-Mann [32] proposed the existence of a conserved Isovector-vector V V current Jm , with ∂mJm = 0. In analogy with the electromagnetic current EM ∂mJm = 0, the renormalization effects on this current had to be zero. The process 14O → 14N is a transition between V hadronic states, nevertheless the coupling gb has to be free of renormalization effects due to Fig. 9 Hand-written sketch by A. Z. of a modern way to illustrate the π → b decay, strong interactions since it is the vector weak the crucial test of (V – A), in terms of “weak colour charges”. It is the W with weak charge which comes in. – + + charges (1 2) (red in the above) which mediates the π → e + ne decay. Weak processes in the hadronic world should V be the ideal case to measure gb provided we are able to choose Isovector-vector transitions such as

This means that

R exp = (1.22 ± 0.30)×10−4 (Ashkin et al.1959[8]) exp −4 The best way to measure g is to study the µ R = (1.21± 0.07)×10 (Anderson et al.1960[30]) µ decay

(the same Anderson who, together with others, This is how, for the first time, the muon lifetime had established the limit of Rexp ≤ 10–5 [28, 29]) τm was measured at CERN (rate independent) [19, 20]. The result is in fig. 11.

Fig. 10 Comparison of exprimental results on Rexp = (π→β / π→µ)

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In terms of the weak charge the result is

V When compared with gb the result is

The weak charge measured in leptonic decays is found to be greater than the weak charge measured in hadronic decays. This was the 1st measurement of a deviation, of the two weak charges in processes not involving strange particles. Notice that Fig. 11 The diagram above [19, 20] shows that the experimental results on t obtained in Chicago and Carnegie were affected by a rate-dependent m systematic effect which invalidated the data. The CERN result was the first without this trouble. This had never been measured before. The conclusion is that Fermi couplings with ∆S = 0 in strong and purely leptonic processes are different. What was known was that the weak charge measured in hadronic processes with ∆S ≠ 0, V gb (∆S ≠ 0), was different and smaller than the weak charge measured in ∆S = 0 processes, V gb (∆S = 0) :

Polarization Measurement According to (V – A) theory, in the µ decay

all positrons had to be polarized, i.e.

Previous experiments indicated a value compatible with zero. An experimental verification was needed. This was done at CERN where the e+ polarization was indeed found to be 100% [33] (fig. 12).

The Isovector-vector conserved current and the existence of the “weak magnetism” The existence of “weak magnetism” predicted a transition between two states of the same isotopic vector.

Fig. 12 First page of the relevant paper [33] on e+ polarization in muon decay.

vol24 / no5-6 / anno2008 > 85 V Jµ ≡ Isovector-vector current Fig. 14 Plot from [36], updated with the latest LEP data, showing the 1, 2 Jµ ≡ Projections on the (1, 2) axes “butterflies” as we know them now. The energy ranges from ADONE to LEP. On the vertical axis the ratio 3 Jµ ≡ Isovector part of the electromagnetic current

versus the centre-of-mass energy in the (e+e–) annihilation on the horizontal axis. Notice that the nominal ADONE energy was just 0.1 GeV below the J/ψ production threshold and 0.7 GeV below the threshold for rd the 3 lepton. Notice also the_ energy gap between SPEAR and PETRA. In this gap there were the (bb) states (Y, Y’, Y’’) discovered at FERMILAB V Fig. 13 Hand-written sketch by A. Z. of Jm components in the strong [37, 38]. The maximum LEP energy is indicated as well_ as the energy isospin space. threshold for the production of a single t and of a (t t ) pair.

Fig. 15 Fractional momentum distribution of charged pions produced in pp collisions at the ISR, i.e. what Gribov defined the QCD Light. The right plot illustrates the QCD Light spectrum once the “Effective Energy” is taken into account [42].

86 < il nuovo saggiatore a. zichichi: The 40th anniversary of eps: gilberto bernardini’s contributions...

The 1st experiment on the existence of “weak magnetism” was thanks to performed by C. S. Wu and collaborators [34] studying the β decay of 12B and 12N. Another prediction concerned the very rare decay p+→ p0 + + + n e e , with the theoretically computed ratio + must be conserved: ∂m Jm = 0. And this is why for the weak coupling measurement in 14O → 14N one should have:

This very difficult experiment was performed successfully by Soergel and collaborators at CERN [35] with the result

with gm measured in the decay process

in excellent agreement with the theoretical prediction. As said before it was found that Let me say a few words on the CVC, the Isovector-vector conserved current of Gell-Mann and Feynman. This was before the introduction of SU(2) × U(1) for the Electroweak Forces. This implies that the weak charge in the hadronic sector The validity of CVC appeared to be on solid basis, due to the is distributed among many hadronic states: this is flavour existence of the “weak magnetism”, thanks to the experiments mixing in ∆S = 0 processes. of C. S. Wu and V. Soergel. V This reinforced the validity of gm ≠ gb (DS = 0). The proposal of Gell-Mann and Feynman was that the 5 His interest in the frontiers of Physics never 1 2 declined: a few examples Isovector-vector non-strange hadronic currents Jm and Jm 3 form, together with Jm , an isotriplet. In the (strong) isospin space the weak currents together with Let me now flash a few examples of Bernardini’s interest in the electromagnetic currents are the projections, on different the new Physics, according to my personal experience. axes, of the same conserved Isovector-vector current (fig. 13): i) The ADONE energy increase. ii) The (Gribov) QCD Light (the “Effective Energy”). iii) The Superworld threshold decrease by nearly three orders of magnitude: the EGM Effect. iv) The Platonic GUT and the real GUT. v) The GAP. 3 The conservation of the EM current ∂m Jm = 0 implies the V 1 2 i) Had Gilberto Bernardini been the Director of Frascati, the conservation of the full vector Jm and of its Jm and Jm components. J/ψ would have been discovered in Italy many years_ before Let me recall that Ting [39] and Richter [40]; and the third lepton (HLHL) production would have been discovered at Frascati [15-18] not at SLAC by Perl [41] (fig. 14).

ii) Another great physicist I would like to recall is Vladimir The transition 14O → 14N is in fact Gribov who pointed out what follows. Newton discovered that light is the sum of different colours: QED. In QCD we have quarks and gluons interacting and producing jets made of many pions, for instance in pp → π + X as shown in fig. 15 (left). This is what Gribov defined: the QCD Light [42]. The “Effective Energy”, as shown in fig. 15 (right), is at its origin, despite + being totally unexpected. i.e. a transition mediated by the weak current Jm which,

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Fig. 16 Plot taken from [44]. The reference numbers in this figure are Fig. 17 The platonic GUT and the real GUT in the action-space α , α , α those appearing in the original paper. ( 1 2 3) [45]. The points have a sequence of 100 GeV in energy. The last point where the “ideal” platonic straight line intercepts the theoretical prediction is at the energy of the Grand Unification. This 16.2 corresponds to EGU = 10 GeV. Other detailed information on the theoretical inputs: the number of fermionic families, NF, is 3; the number of Higgs particles, NH, is 2; the input value of one of the gauge couplings 0 at the Z -mass is α3(MZ) = 0.118 ± 0.008; the other input is the ratio of weak and electromagnetic couplings also measured at the Z0-mass 2θ ± value: sin W (MZ) = 0.2334 0.0008.

α , α , α iii) Let me now show the most exact use of the iv) The platonic and the real evolution of the ( 1 2 3) renormalization group equations for the running of the three couplings towards the Grand Unification point is illustrated in α , α , α gauge couplings ( 1 2 3) [43-48]. fig. 17, as derived in [45]. During more than ten years (from 1979 to 1991), no one had realized that the energy threshold for the existence of the v) The existence of a GAP between the GUT scale and the Superworld was strongly dependent on the running of the Planck scale is sketched in fig. 18 and detailed in fig. 19. masses and that unification had consequences on the low- The mathematical formalism [44] which has been used to energy threshold [44]. This is now called: the EGM Effect (from obtain the results shown in these figures is a system of three the initials of Evolution of Gaugino Masses). differential non-linear equations coupled via the gauge α α To compute the energy threshold using only the running of couplings i, j as shown below (with i = 1, 2, 3; and j = 1, 2, 3 α , α , α ≠ the gauge couplings ( 1 2 3) corresponds to neglecting but i j): nearly three orders of magnitude in the energy threshold for the discovery of the lightest particle of the Superworld (LSP), as illustrated in fig. 16.

88 < il nuovo saggiatore a. zichichi: The 40th anniversary of eps: gilberto bernardini’s contributions...

Fig. 18 The graph [46] shows the evolution of the gauge couplings and the existence of the GAP.

Fig. 19 The graph [47] shows the results of a detailed study concerning the energy level where the unification of the gauge couplings occurs, as a function of the various parameters needed, including the experimental uncertainties.

6 His enthusiasm as testified by Leon Lederman

Bernardini’s enthusiasm, towards new discoveries, never went down. Let me close with the testimony by Leon Lederman (fig. 20).

THE PLEASURE OF LEARNING: how an Italian visitor rekindled the joy of Science in a war veteran [49] Picking up the threads of normal life after a war is difficult, even when you are on the winning side. In 1946, returning from the Second World War, I registered at Columbia University, New York, as a graduate student in physics. That ensuing year was the worst that I can Fig. 20 Leon Lederman, Director Emeritus of Fermi National Accelerator Laboratory. recall. The classes were crowded with veterans returning

vol24 / no5-6 / anno2008 > 89 Fig. 21 The CERN, now. The large white circumference indicates the 27-kilometer-long magnetic track of the LEP machine and of the LHC collider (10% ELN) of CERN.

90 < il nuovo saggiatore a. zichichi: The 40th anniversary of eps: gilberto bernardini’s contributions...

Fig. 22 The Electroweak sector of the Standard Model.

Fig. 23 The QCD sector of the Standard Model.

from military service or from research in the various laboratories the physics journals. ... that had supported the war. Bernardini had had a very difficult time in Italy during the war. The teaching faculty was also just beginning to return, and Arriving in Columbia he was – if anything – as insecure as I was. so most of the courses were taught by Isidor Isaac Rabi (the But he soon started to change my insecurity and restore my chairman of the physics department, and winner of the Nobel original enthusiasms. He was “in touch”. Through Enrico Fermi, prize for physics, 1944) and Willis Lamb, who was also to win a his teacher, he knew the latest physics gossip and therefore he Nobel prize in 1955. Rabi exuded charisma and enthusiasm. ... stimulated ideas on how to use the new accelerator. ... Bernardini About midway through my second year, I applied for a research taught me the marvels of familiar phenomena. He would even position. Columbia was building a particle accelerator and they turn on the lights in the laboratory, and turn them off and would need instruments and people who could be involved in on again. How did this happen? What series of phenomena the new “high-energy physics”. ... were organized to bring us light? In my subsequent 40 years In 1948, I spent about a month away from the laboratory of research, there have been times of stress, frustation and studying for my PhD qualifying exams. Exam-taking, especially disappointment. for me, was traumatic and I looked forward to continuing to test These are suffered in the hope that a discovery will bring the cloud-chamber device that we had designed from reading everlasting joy, fame and fortune. But this is not a life. The fun the literature. and excitement must be daily, in the challenge of creating an Returning to the laboratory, I found a fellow mopping the floor instrument and seeing it work, the joy of communicating to and singing a fragment of Italian opera. ...It took another 20 colleagues and students, the pleasure of learning something minutes to clarify that Gilberto Bernardini was ... a visiting new, in lectures, corridors and journals. And underlying it all, the professor from Rome with a very distinguished career in cosmic- sense of wonder that nature is comprehensible. The Italian visitor ray physics. His English was primitive, mostly learned by reading was my turning point.

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Conclusion

We now have the LHC (fig. 21). This can be regarded as the present 10% scale implementation of a much larger project: the Eloisatron (ELN) (see for instance [50]). We have also the Standard Model, based on SU(2) × U(1) × SU(3). This is schematically illustrated in figs. 22 and 23. An exhaustive review can be found in [50]. But we are still left with a series of open questions beyond the Standard Model that will be our challenges for the future (fig. 24).

Gilberto Bernardini was not only a great physicist and a strong supporter of advanced physics projects. He also wanted to unify the physics community. In Italy this gave the result of creating the INFN and being its first President; in Europe contributing to the birth of CERN and of its first great discoveries, and creating EPS, being its first President.

Gilberto Bernardini Institutions

INFN - 1st President CERN - 1st Research Director EPS - 1st President

As stated by Enrico Fermi: “Neither Science nor Civilization could exist without memory.” This means that we have to pay a tribute to Gilberto Bernardini for all his activity as Man, Scientist and Physicist. Finally, let me end up by showing a picture of 40 years ago during his Opening Lecture at Erice when the EMFCSC was Fig. 24 The Standard Model and beyond. just 5 years old (fig. 25).

References [8] J. Ashkin, T. Fazzini, G. Fidecaro, A. W. Merrison, H. Paul and A. V. Tollestrup, “The electron decay mode of the pion”, Il Nuovo [1] A. Zichichi, “Creativity in Science”, World Scientific - The Science and Cimento, 13 (1959) 1240. Culture Series - Advanced Scientific Culture, vol. 1 (World Scientific) [9] G. Charpak, F. J. Farley, R. L. Garwin, T. Muller, J. C. Sens, V. L. Telegdi 1999. and A. Zichichi, “Measurement of the anomalous magnetic moment [2] “Proceedings of the International Conference on Elementary of the muon”, Phys. Rev. Lett., 6 (1961) 128. Particles”, Pisa, 12-15 June 1955, Il Nuovo Cimento, 4, Suppl. 4 [10] G. Charpak, F. Farley, R. L. Garwin, T. Muller, J. C. Sens, V. L. Telegdi, (1956) 325. C. M. York and A. Zichichi, “The anomalous magnetic moment of the [3] M. Gell-Mann, A. Pais, “Behaviour of neutral particles under charge muon”, in Proceedings of the International Conference on High- conjugation”, Phys. Rev., 97 (1955) 1387. Energy Physics, Rochester, NY, 25 August-1 September 1960, (Univ. [4] G. Puppi (Editor), “Old and New Problems in Elementary Particles” Rochester, NY) 1960, p. 778. (Academic Press)1968. [11] G. Charpak, F. J. Farley, R. L. Garwin, T. Muller, J. C. Sens and [5] G. Puppi, “Sui mesoni dei raggi cosmici”, Il Nuovo Cimento, 5 (1948) A. Zichichi, “A new measurement of the anomalous magnetic 587. moment of the muon”, Phys. Lett., 1 (1962) 16. [6] M. Conversi, E. Pancini and O. Piccioni, “On the disintegration of [12] G. Charpak, F. J. Farley, R. L. Garwin, T. Muller, J. C. Sens and negative mesons”, Phys. Rev. Lett., 71 (1947) 209. A. Zichichi, “(g − 2) and its consequences”, in Proceedings of the [7] T. Fazzini, G. Fidecaro, A. W. Merrison, H. Paul and A. V. Tollestrup, International Conference on High-Energy Physics, Geneva, 4 -11 “Electron decay of the pion”, Phys. Rev. Lett., 1 (1958) 247. July l962, (CERN, Geneva) 1962, p. 476.

92 < il nuovo saggiatore a. zichichi: The 40th anniversary of eps: gilberto bernardini’s contributions...

Fig. 25 Photo of Gilberto Bernardini giving the Opening Lecture at the International School of Physics “Ettore Majorana” (Erice, 1968); 1st from left M. Schwartz, then T. D. Lee, A. Z., I. I. Rabi, G. Bernardini and S. Frautschi.

[13] G. Charpak, F. J. Farley, R. L. Garwin, Th. Muller, J. C. Sens and [18] M. Bernardini, D. Bollini, P. L. Brunini, E. Fiorentino, T. Massam, A. Zichichi, “The anomalous magnetic moment of the muon”, Il L. Monari, F. Palmonari, F. Rimondi and A. Zichichi, “Limits on the Nuovo Cimento, 37 (1965) 1241. mass of heavy leptons”, Il Nuovo Cimento A, 17 (1973) 383. [14] L. Maiani and A. Zichichi, “Dal Gran Sasso al Supermondo”, INFN/AE- [19] F. J. Farley, T. Massam, T. Muller and A. Zichichi, “A measurement 98/19, July 1998. of the µ+ lifetime”, in Proceedings of the International Conference [15] C. S. Wu, T. D. Lee, N. Cabibbo, V. F. Weisskopf, S. C. C. Ting, C. Villi, on High-Energy Physics, Geneva, 4-11 July 1962, (CERN, Geneva) M. Conversi, A. Petermann, B. H. Wiik and G. Wolf, “The Origin of the 1962, p. 415. Third Family”, edited by L. Maiani et al., World Scientific Series in 20th [20] A. Zichichi, “CERN work on weak interactions” in the February 1964 Century Physics, vol. 20 (1998). Meeting of the Royal Society, Proc. R. Soc. Ser. A, 285 (1965) 175. [16] M. Bernardini, D. Bollini, E. Fiorentino, F. Mainardi, T. Massam, [21] G. Bernardini et al., “Spark chamber study on the elastic production L. Monari, F. Palmonari and A. Zichichi, “A proposal to search for of muons and electrons by high-energy neutrinos”, in Proceedings of leptonic quarks and heavy leptons produced by ADONE”, INFN/AE- the 12th International Conference on High Energy Physics, Dubna, 67/3, 20 March 1967. August 1964, vol. 2 (Atomizdat, Moscow)1966, p. 20. [17] V. Alles-Borelli, M. Bernardini, D. Bollini, P. L. Brunini, [22] A. Zichichi, “Attuale stato della fisica delle interazioni deboli”, Il T. Massam, L. Monari, F. Palmonari, and A. Zichichi, “Limits on the Nuovo Cimento, 3, Suppl. 4 (1965) 894. electromagnetic production of heavy leptons”, Lett. Nuovo Cimento, [23] M. Ageno, N. B. Cacciapuoti, B. Ferretti, G. Bernardini, G. C. Wick, 4 (1970) 1156. “The anomalous absorption of the hard component of cosmic rays in air”, Phys. Rev. , 57 (1940) 945.

vol24 / no5-6 / anno2008 > 93 [24] G. Bernardini and E. L. Goldwasser, “Photoproduction of p+ mesons [38] W. R. Innes, J. A. Appel, B. C. Brown, C. N. Brown, K. Ueno, from hydrogen near threshold”, Phys. Rev., 94 (1954) 729. T. Yamanouchi, S. W. Herb, D. C. Hom, L. M. Lederman, J. C. Sens, [25] M. Beneventano, G. Bernardini, D. Carlson-Lee, G. Stoppini and H. D. Snyder, J. K. Yoh, R. J. Fisk, A. S. Ito, H. Jöstlein, D. M. Kaplan, L. Tau, “Differential cross-sections for photoproduction of positive and R. D. Kephart, “Observation of structure in the Y region”, Phys. pions in hydrogen”, Il Nuovo Cimento, 4 (1956) 323. Rev. Lett., 39 (1977) 1240. [26] C. M. G. Lattes, H. Muirhead, G. P. S. Occhialini and C. F. Powell, [39] J. J. Aubert, U. Becker, P. J. Biggs, J. Burger, M. Chen, G. Everhart, “Processes involving charged mesons”, Nature, 159 (1947) 694. P. Goldhagen, J. Leong, T. McCorriston, T. G. Rhoades, M. Rohde, [27] C. M. G. Lattes, G. P. S. Occhialini and C. F. Powell, “Observations on Samuel C. C Ting and Sau Lan Wu, “Experimental observation of a the tracks of slow mesons in photographic emulsions”, Nature, 160 heavy particle J”, Phys. Rev. Lett., 33 (1974) 1404. (1947) 454. [40] J.-E. Augustin, A. M. Boyarski, M. Breidenbach, F. Bulos, J. T. Dakin, [28] H. L. Anderson and C. M. G. Lattes, “Search for the electronic decay of G. J. Feldman, G. E. Fischer, D. Fryberger, G. Hanson, B. Jean-Marie, the positive pion”, Il Nuovo Cimento, 6 (1957) 1356. R. R. Larsen, V. Lüth, H. L. Lynch, D. Lyon, C. C. Morehouse, [29] S. Lokanathan and J. Steinberger, “Search for the β-decay of the J. M. Paterson, M. L. Perl, B. Richter, P. Rapidis, R. F. Schwitters, pion”, Il Nuovo Cimento, 10 (1955) 151. W. M. Tanenbaum, and F. Vannucci, “Discovery of a narrow [30] H. L. Anderson, T. Fujii, R. H. Miller, and L. Tau, “Branching ratio of resonance in e+e– annihilation”, Phys. Rev. Lett,. 33 (1974) 1406. the electronic mode of positive pion decay”, Phys. Rev., 119 (1960) [41] M. L. Perl et al., “Evidence for anomalous lepton production in 2050. e+e– annihilation”, Phys. Rev. Lett., 35 (1975) 1489. [31] G. Danby, J.-M. Gaillard, K. Goulianos, L. M. Lederman, N. Mistry, [42] For a complete set of references concerning this topic see: M. Schwartz and J. Steinberger, “Observations of high-energy V. N. Gribov, G. ‘t Hooft, G. Veneziano and V. F. Weisskopf, “The neutrino reactions and the existence of two kinds of neutrinos”, Phys. Creation of Quantum ChromoDynamics and the Effective Energy”, Rev. Lett., 9 (1962) 36. edited by N. L. Lipatov, World Scientific Series in 20th Century [32] R. P. Feynman and M. Gell-Mann, “Theory of the Fermi interaction”, Physics, vol. 25 (World Scientific) 2000. Phys. Rev., 109 (1958) 193. [43] F. Anselmo, L. Cifarelli, A. Petermann and A. Zichichi, “The [33] A. Buhler, N. Cabibbo, M. Fidecaro, T. Massam, Th. Muller, simultaneous evolution of masses and couplings: consequences on M. Schneegans and A. Zichichi, “A measurement of the e+ supersymmetry spectra and thresholds”, Il Nuovo Cimento A, 105 polarization in muon decay: the e+ annihilation method”, Phys. Lett., (1992) 1179. 7 (1963) 368. [44] F. Anselmo, L. Cifarelli, A. Peterman and A. Zichichi, “The evolution [34] Y. K. Lee, L. W. Mo, and C. S. Wu, “Experimental test of the conserved of gaugino masses and the SUSY threshold”, Il Nuovo Cimento A, 105 vector current theory on the beta spectra of B12 and N12 “, Phys. Rev. (1992) 581. Lett., 10 (1963) 253. [45] F. Anselmo, L. Cifarelli, A. Peterman and A. Zichichi, “The effective

[35] P. Depommier, J. Heintze, A. Mukhin, C. Rubbia, V. Soergel and experimental constraints on MSUSY and MGUT “, Il Nuovo Cimento A, K. Winter, “Determination of the p+ → p0 + e+ + n decay rate”, Phys. 104 (1991) 1817. 2 Lett., 2 (1962) 23. [46] F. Anselmo, L. Cifarelli, A. Zichichi, “A χ -test to study the α1, α2, α3 [36] A. Zichichi, “First search for sequential heavy leptons at ADONE”, convergence for high precision LEP data, having in mind the SUSY CERN-PPE/93-58 and CERN/LAA/93-18, 2 April 1993. Presented threshold”, Il Nuovo Cimento A, 105 (1992) 1357. at the Symposium on “The τ particle”, in honour of Martin Perl’s [47] F. Anselmo, L. Cifarelli and A. Zichichi, “A study of the various

65th birthday, SLAC, Stanford, CA, 24 July 1992; Proceedings. of approaches to MGUT and αGUT ” , Il Nuovo Cimento A, 105 (1992) 1335. the Summer Institute on Particle Physics “The Third Family and the [48] S. Ferrara and R. M. Mössbauer (Editors), “Searching for the Physics of Flavor”, edited by L. Vassilllian, SLAC CONF-9207140 UC- Superworld”, World Scientific Series in 20th Century Physics, vol. 39 414 (T/E) 1993, p. 603. (World Scientific) 2007. [37] S. W. Herb, D. C. Hom, L. M. Lederman, J. C. Sens, H. D. Snyder, [49] L. Lederman, “The pleasure of learning”, Nature, 430 (2004) 617. J. K. Yoh, J. A. Appel, B. C. Brown, C. N. Brown, W. R. Innes, K. Ueno, [50] A. Zichichi, “Subnuclear Physics – The first 50 years: Highlights T. Yamanouchi, A. S. Ito, H. Jöstlein, D. M. Kaplan and R. D. Kephart, from Erice to ELN”, edited by O. Barnabei, P. Pupillo and F. Roversi “Observation of a dimuon resonance at 9.5 GeV in 400 GeV proton- Monaco, World Scientific Series in 20th Century Physics, vol. 24 nucleus collisions”, Phys. Rev. Lett., 39 (1977) 252. (World Scientific) 2000.

Antonino Zichichi Antonino Zichichi is the author of advanced research work concerning the fundamental building blocks of matter and the fundamental forces of nature. He has published over 900 scientific papers, some of which have opened new avenues in subnuclear physics at high energies. He has received awards and honorary degrees from Universities and Academic Institutions in Italy and in many other countries, including Argentina, China, Georgia, Germany, Poland, Romania, Russia, Ukraine and USA. He founded and directs the “Ettore Majorana” Foundation and Centre for Scientific Culture, Erice. He is Emeritus Professor of Advanced Physics at the University of Bologna; Past President of the INFN (Italian National Institute for Nuclear and Subnuclear Physics); Past President of the EPS (European Physical Society); Past President of the NATO Science Committee for Disarmament Technology; President of the World Federation of Scientists; President of the “Enrico Fermi Centre”, Rome. He is member of the Pontificial Academy of Sciences, the Academia Europaea, and other Academies. In 2001 he has been awarded the “Enrico Fermi” Prize of the Italian Physical Society for his discovery of nuclear antimatter, and in 2007 the JINR “Bruno Pontecorvo” Prize for the original method he proposed to search for a third heavy lepton in uncorrelated electron-muon pairs.

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Il premio Nobel per la fisica 2008

Alessandro Bettini* Dipartimento di Fisica “G. Galilei” e INFN, Università di Padova, Padova, Italia Laboratorio Subterráneo de Canfranc, Canfranc (Huesca), Spagna

1 Motivazioni e vincitori studi fu arruolato nell’esercito, ma ebbe la fortuna di rimanere Il premio Nobel per la fisica 2008 è stato assegnato per le in Giappone, impiegato nella ricerca sui radar. Finita la guerra “Broken Symmetries”, cioè per le simmetrie violate, o “rotte”. ottenne una posizione di post-doc all’Università di Tokyo, Tutti i fisici conoscono l’importanza dei principi di simmetria, entrando successivamente a far parte del gruppo di Sin-Itiro che dominano la fisica dell’ultimo secolo, e tutti i fisici Tomonaga. sanno che la natura non segue quasi mai perfettamente Tomonaga stesso lo presentò ad Oppenhaimer che gli fece una legge di simmetria, ma in generale la viola un po’. avere una borsa di studio a Princeton. Da Princeton, Nambu Solo una così vasta motivazione poteva comprendere i si spostò a Chicago, e il soggiorno negli Stati Uniti, invece di contributi, così distanti tra loro, durare un paio di anni, delle due metà in cui il premio è è durato tutta la vita. stato diviso. Ha lasciato tuttavia Nambu è professore perplessità l’esclusione di Nicola emerito dell’Istituto Enrico Cabibbo, che pose le basi teoriche Fermi dell’Università di del mescolamento dei quark, Chicago. successivamente esteso da L’altra metà del premio Kobayashi e Maskawa. è stata assegnata Conviene comunque leggere le congiuntamente a Makoto argomentazioni della Classe di Kobayashi e a Toshihide Fisica dell’Accademia Reale Svedese Maskawa (fig. 2 e 3) per la delle Scienze, nella nota “Broken scoperta di quella rottura Symmetries” [1], all’indirizzo di simmetria che porta alla http://nobelprize.org/ predizione dell’esistenza nobel_prizes/physics/ in natura di almeno tre laureates/2008/. Quando famiglie di quark. queste note saranno stampate Entrambi sono della si potranno trovare al medesimo scuola di Nagoya. indirizzo anche le lezioni Nobel dei Maskawa, nato nel 1940, premiati, la cui lettura permetterà si diplomò a Nagoya certamente una più profonda nel 1962, dove ricevette Fig. 1 Yoichiro Nambu. visione della fisica. anche il titolo di PhD nel Una metà del premio è stata 1967. Dopo un periodo assegnata a Yoichiro Nambu (fig. )1 per la scoperta della di ricercatore associato all’Università di Nagoya divenne rottura spontanea della simmetria a livello subatomico. professore all’INS (Institute of Nuclear Studies) dell’Università Nambu, nato a Tokyo nel 1921, si iscrisse all’Università pochi di Tokyo e successivamente all’YITP (Yukawa Institute for anni prima dell’inizio della guerra mondiale. Terminati gli Theoretical Physics) all’Università Sangyo di Kyoto, dove è attualmente professore emerito. *e-mail: [email protected]. Kobayashi, nato nel 1944, si diplomò nel 1967 a Nagoya,

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Fig. 2 Toshihide Maskawa. Fig. 3 Makoto Kobayashi.

dove ricevette anche il PhD nel 1972. Dopo un periodo di Ma non perfettamente, ci sono delle piccole differenze. ricercatore associato all’Università di Kyoto si spostò come Esse certamente rendono più piacevole un volto, rispetto professore al Laboratorio Nazionale di Fisica delle Alte Energie a quello che sarebbe se fosse perfettamente simmetrico. A (KEK) a Tsukuba, dove diresse l’Istituto di studi nucleari e di livello microscopico, le interazioni fondamentali sono solo particelle e dove è tuttora professore emerito. parzialmente invarianti sotto l’inversione degli assi, o, in maniera equivalente, di uno di essi, come nella riflessione in uno specchio. Lo sono la lagrangiana delle interazioni forti 2 Simmetrie e gruppi e quella delle interazioni elettromagnetiche, ma non quella Le leggi della fisica non cambiano al passare degli anni, né delle deboli. La simmetria quindi non è esatta, è rotta e dipendono dal luogo nel quale avvengono i fenomeni. Galileo l’osservabile “parità” non è sempre conservato. Galilei stabilì inoltre che esse obbediscono al principio di Questo tipo di rottura di simmetria, le piccole irregolarità del relatività, cioè non dipendono dal moto relativo, purché esso volto o la non invarianza di una parte della lagrangiana, si sia traslatorio uniforme. Henri Poincaré [2] stabilì nel 1905 dice “esplicita”. Le interazioni deboli, che non sono invarianti che l’insieme di queste trasformazioni, traslazioni, rotazioni né, come detto, sotto l’operazione di parità P, né per lo e trasformazioni di Lorentz, costituisce un gruppo, nel senso scambio, “coniugazione”, particella-antiparticella C, lo sono matematico del termine. Emmi Noether [3] dimostrò nel 1918 quasi per la combinazione delle due, CP. Furono Kobayashi che alle proprietà di invarianza corrispondono osservabili e Maskawa a comprendere nel 1973 che l’origine della, fisici conservati. In particolare, all’invarianza sotto il gruppo piccolissima, violazione di CP poteva essere compresa se ci di Poincaré corrispondono le conservazioni dell’energia, fossero stati in natura due quark in più rispetto ai quattro della quantità di moto e del momento angolare che non allora noti, estendendo ad essi la teoria del mescolamento di conoscono eccezioni. L’invarianza di Poincaré è quindi una Cabibbo, come discuteremo in seguito. simmetria esatta. Un altro tipo importante di simmetria è quello delle simmetrie Non tutte le simmetrie sono però esatte. La natura esprime interne. La prima fu la simmetria dell’isospin, introdotta la simmetria imperfetta a tutti i livelli. Gli esempi sono da Werner Heisenberg nel 1932 [4] per rappresentare parte dell’esperienza quotidiana. Ad esempio, i nostri corpi, l’invarianza delle forze nucleari per la sostituzione, nelle e quelli degli animali, sono esteriormente simmetrici per dovute condizioni, protone-neutrone. Il gruppo di simmetria riflessione rispetto al piano verticale che ci dimezza: la è SU (2). Il protone e il neutrone formano assieme un parte sinistra è uguale alla destra riflessa in uno specchio. doppietto di isospin. Sono quindi due stati della stessa

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particella e come tali dovrebbero avere la stessa massa. In rottura spontanea di simmetria è conosciuto per sistemi effetti ce l’hanno quasi uguale, perché la simmetria non è macroscopici da moltissimi anni. Tali sono il ferromagnetismo perfetta. Dopo la scoperta delle particelle strane, nel 1956 e la superconduttività. Shoichi Sakata [5] propose di considerare come fondamentali, Sorprendentemente, la rottura spontanea di simmetria è oltre al protone e al neutrone, anche un barione strano, presente anche a livello fondamentale, per sistemi quantistici la Λ. I “sapori” degli adroni erano tre, le due componenti “semplici” come le particelle elementari, come stabilito dell’isospin e la stranezza. Nel 1961, Murray Gell-Mann principalmente dai lavori di Nambu e di Goldstone all’inizio [6] e indipendentemente Yuval Ne′eman [7] proposero degli anni 1960. Anzi, la rottura spontanea è un aspetto di estendere la simmetria (rotta) interna degli adroni al essenziale del Modello Standard e, in particolare i bosoni di gruppo SU (3). Tre anni dopo, nel 1964 George Zweig [8] Nambu-Goldstone (corrispondenti all’onda dell’analogia) ne e indipendentemente Gell-Mann [9] compresero che la sono componenti fondamentali. simmetria SU(3) si poteva comprendere come dovuta a tre componenti, chiamati “assi” da Zweig e “quark” da Gell-Mann, uno per ogni sapore. Sono chiamati rispettivamente up, down 3 Le interazioni fondamentali e strano, u, d e s. Hanno gli stessi numeri quantici dei barioni Il Modello Standard delle interazioni fondamentali descrive p, n e Λ del modello di Sakata, tranne che le loro cariche in maniera rigorosamente testata tutte le interazioni elettriche sono frazionarie, 2/3, –1/2 e –1/3, rispettivamente. fondamentali, tranne la gravitazione. È necessario qui Il modello a quark rivelò subito la sua utilità per spiegare richiamarne, sia pure sommariamente, alcuni aspetti. Si ricordi in maniera semplice lo spettro degli adroni, sia barioni sia però che al tempo delle scoperte premiate, esisteva una mesoni, che sia era arricchito di una miriade di elementi. La descrizione teorica solo dell’interazione elettromagnetica. Per realtà fisica dei quark come componenti elementari degli le altre venivano avanzati diversi tentativi di interpretazione adroni fu però accettata solo nel 1967, quando Jerome teorica. Solo alcuni di questi si rivelarono corretti. Citeremo Friedman, Henry Kendall e Richard Taylor [10] e i loro gruppi nel seguito alcune delle principali scoperte, ma ricordiamo risolsero la struttura interna del protone col fascio di elettroni che in generale le scoperte non sono istantanee, ma di SLAC. La sua energia di 20 GeV consentiva di raggiungere piuttosto sono spesso precedute da tentativi precursori che un potere risolutivo di una piccola frazione di femtometro. cominciano ad abbozzarle. Sappiamo oggi che esistono in totale tre “famiglie” di I processi fisici fondamentali che osserviamo sono il particelle elementari, tutte con la stessa struttura. Ciascuna decadimento di una particella in due o più particelle e l’urto contiene un quark di tipo up (cioè di carica 2/3), e uno di tipo tra due particelle che produce due o più altre particelle down (carica –1/3), un leptone carico e il suo neutrino. Sono nello stato finale. In entrambi i casi il processo è istantaneo, , rispettivamente (u, d, e, νe), (c, s, µ, νµ) e (t, b, τ ντ). Tre dei rispetto ai tempi di misura. In entrambi i casi, osserviamo quark hanno massa piccola, u di circa 3 MeV, d di circa 6 MeV la scomparsa delle particelle iniziali e la comparsa di quelle e s di circa 100 MeV. Gli altri tre hanno masse molto più grandi finali. La funzione matematica che descrive il processo è la e furono quindi scoperti più tardi. lagrangiana corrispondente alle interazioni in gioco. Esiste un altro modo, più sottile, di violare la simmetria. Il Tutte le lagrangiane d’interazione, elettromagnetica, debole sistema, matematicamente la sua lagrangiana, può essere e forte, contengono espressioni, chiamate correnti, che perfettamente simmetrico, ma i suoi stati possono non includono i campi delle particelle fermioniche, quark e esserlo. A livello macroscopico ciò avviene per sistemi leptoni. Le correnti elettromagnetica e forte sono vettoriali, composti da moltissimi elementi (atomi, molecole) uguali tra cioè hanno momento angolare 1 e parità negativa, le loro. Pensiamo, come similitudine, ad un branco di pesci (o correnti deboli hanno una componente vettoriale ed una ad uno sciame d’uccelli) tutti uguali tra loro. Supponiamo che assiale (momento angolare 1 e parità positiva). Le correnti la superficie del mare ed il suo fondo siano distanti e che il si accoppiano con i bosoni mediatori dell’interazione, che peso sia perfettamente bilanciato dalla spinta di Archimede. sono tutti vettori: il fotone per l’elettromagnetismo, W+, W− e Allora tutte le direzioni sono equivalenti, l’ambiente è Z0 per l’interazione debole e gli otto gluoni per l’interazione simmetrico. Eppure, un pesce del branco decide di scegliere forte. una direzione in cui dirigersi e, dopo un po’, tutti gli altri lo Così l’interazione elettromagnetica_ degli elettroni è descritta imitano. La simmetria si è rotta “spontaneamente”. A meglio dal_ prodotto della corrente egme del campo fotonico Aµ e di guardare, il processo è graduale. All’inizio sono pochi i pesci √a, dove α è la costante di struttura fina, proporzionale al che hanno scelto la direzione in cui muoversi, localizzati quadrato della carica elementare. Nell’espressione scritta e in una piccola regione di spazio. Poi la scelta si propaga a è il campo dell’elettrone, un bispinore di Dirac, e sono le _ γµ tutto il gruppo muovendosi un po’ come un’onda. È l’onda matrici di Dirac. Quindi egme è una quantità vettoriale. Esiste di Nambu-Goldstone. Fuori di metafora, il fenomeno della una corrente vettoriale per ogni quark e per ogni leptone. Le

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correnti dei neutrini compaiono solo nelle interazioni deboli. accoppiamento delle correnti deboli cariche è universale, cioè Ad esempio la diffusione elastica di un elettrone e di un la stessa per tutte. È la costante di Fermi, che viene misurata - m- → - + m- µ muone e + e è _ottenuta_ come sequenza_ _ di in maniera precisa misurando_ la massa del e la velocità del √a ( g ) m √a (mg m) m m- → - + n sottoprocessi descritti da e m e A e da m A . decadimento e e + νµ . Caso più semplice: primo sottoprocesso: l’elettrone iniziale All’inizio degli anni 1960, quando erano noti solo tre sapori, scompare e appaiono l’elettrone finale e un fotone; secondo la situazione era confusa perché la velocità del decadimento sottoprocesso: il fotone viene assorbito dal muone iniziale, beta del neutrone (e di alcuni nuclei) era solo circa il 97% di assieme scompaiono e compare il muone finale. quanto previsto dall’universalità e, ancor peggio, le velocità Le interazioni deboli sono di gran lunga più complicate. dei decadimenti di particelle strane in particelle senza Anzitutto ne esistono di due tipi, quelle mediate dalla Z0, stranezza erano un ordine di grandezza troppo piccole. Il chiamate di “corrente neutra” e quelle mediate da W + e W –, problema fu risolto da Nicola Cabibbo [11] che introdusse nel dette di “corrente carica”. Nell’interazione elettromagnetica 1963 il concetto di mescolamento tra i sapori (col linguaggio la carica delle particelle presenti prima e dopo l’emissione di oggi): la corrente debole carica adronica (quella che o assorbimento del fotone è la stessa, perché la carica si sappiamo oggi si accoppia con la W) è una combinazione conserva e il fotone non ha carica. Altrettanto avviene della corrente che non cambia la stranezza, diciamola

per le interazioni deboli di corrente neutra. Le interazioni J|DS|=0, e di quella che la cambia J|DS|=1. La combinazione si deboli mediate da W + e W – invece, per le medesime ragioni, può esprimere come una rotazione attraverso un angolo, cambiano la carica della particella. Ad esempio un elettrone chiamato angolo di Cabibbo può scomparire mentre compaiono un neutrino elettronico e una W –. (3) Una seconda differenza importante è che esistono correnti deboli sia vettoriali sia assiali. Le prime hanno_ forma analoga Il punto importante è che tutte le velocità di decadimento alla corrente elettromagnetica, cioè del tipo eg e, ma anche in leptoni degli adroni e dei leptoni sono predette _ _m n g n g g ad esempio e m e, quelle assiali sono del tipo e m 5e. correttamente con lo stesso valore dell’angolo. L’universalità La_ corrente vettoriale carica, ad_ esempio per l’elettrone, è era così stabilita in forma nuova. Considerazioni analoghe n g nn g g e me, mentre quella assiale è e m 5e. erano state avanzate nel 1960 da M. Gell-Mann e M. Levy [12] Tutte_ le correnti deboli cariche sono del tipo V – A, cioè in una nota a piè pagina. n g - g ) e m (1 5 e . Dopo l’introduzione del concetto di quark, che come già Data questa struttura, si definiscono le proiezioni chirali degli ricordato avvenne l’anno successivo, divenne chiaro che la spinori ψ di Dirac, dette rispettivamente “left” (L) e “right” (R) teoria di Cabibbo implicava che il quark di tipo down che si accoppia al quark u non è né d né s, ma il campo ottenuto dalla rotazione (1) , (4) È facile vedere che la corrente V – A, nell’esempio considerato, _ g si può scrivere La corrente adronica debole carica è quindi d ’L muL. Veniva così stabilito il concetto di mescolamento tra quark. (2)

Quindi, solo le componenti di chiralità negativa hanno 4 Rottura spontanea interazione debole carica. La chiralità però non è in genere La rottura spontanea di una simmetria avviene quando la un osservabile. Lo sarebbe se la particella (di spin ½) avesse lagrangiana del sistema è simmetrica, ma non lo è lo stato di massa nulla. In questo limite essa coincide con l’elicità, minima energia cioè, come si dice, il vuoto. Quando Nambu che è la proiezione dello spin sulla direzione del moto ed cominciò ad occuparsi del problema situazioni del genere è misurabile. Benché tutte le particelle di spin ½, abbiano erano note da diversi decenni per sistemi composti da massa, esistono situazioni in cui essa è piccola, o addirittura molte particelle. Ad esempio in un dominio ferromagnetico trascurabile, rispetto all’energia. i momenti magnetici responsabili del magnetismo scelgono La corrente debole carica (2) è quella che accoppia l’elettrone spontaneamente una delle due orientazioni di energia al suo neutrino. Altre due, del tutto analoghe, accoppiano il minima, rompendo la simmetria. In un superconduttore il leptone µ al suo neutrino e il leptone τ al suo neutrino. Per i condensato nello stato di energia minima è composto di quark ci sono anche tre correnti che accoppiano un quark di coppie di Cooper, che hanno carica non nulla (–2) rompendo tipo up e uno di tipo down. Sappiamo ora che la costante di la simmetria dell’elettrodinamica.

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Nel 1960 Nambu avanzò l’ipotesi ardita che la rottura spettro dei mesoni dovrebbero esistere sia particelle spontanea di simmetria potesse aver luogo anche nelle pseudoscalari, cioè di spin 0 e parità negativa, sia scalari teorie di campo delle particelle elementari. Sviluppò (spin 0, parità positiva), con masse uguali. Limitiamoci per successivamente le idee in una serie di lavori da solo e con semplicità ai mesoni non strani, che contengono cioè i quark collaboratori [13]. u e d. La simmetria chirale per essi è SU(2) × SU(2). Si vede Il vuoto a livello delle particelle elementari, lo stato di energia che i bosoni di Goldstone corrispondenti alla sua rottura minima, è una regione di spazio in cui non sono presenti sono quattro di egual massa: tre pseudoscalari in un tripletto né particelle né campi di forza. Sembrerebbe a prima vista di isospin, e uno scalare singoletto. Il tripletto isoscalare è che non ci fosse nulla. Invece, l’indagine iniziata da Nambu formato dai tre pioni. Il mesone scalare esiste, ma non era ha mostrato che il vuoto quantistico, quando osservato a noto al tempo dei lavori in discussione. Anche se la prima scale dell’ordine di una frazione di femtometro, è un mezzo evidenza sperimentale risale al 1968 [16], ci vollero molti dinamico estremamente attivo nel quale continuamente anni per stabilirne fermamente l’esistenza. La sua massa al coppie particella antiparticella si formano per fluttuazione quadrato è di due ordini di grandezza maggiore di quella del quantistica e subito si annichilano nuovamente. pione. È questo l’effetto della rottura sia esplicita (masse non Un altro contributo fondamentale fu portato da Jeffrey nulle dei quark u e d) sia spontanea (vuoto degli stati adronici Goldstone nel 1961 [14]. Egli dimostrò che la rottura asimmetrico) della simmetria chirale. spontanea di una simmetria esatta, cioè non esplicitamente Più in generale, il concetto di rottura spontanea è un rotta, implica l’esistenza di una o più particelle di spin zero di elemento essenziale del Modello Standard. Nello sviluppo massa nulla, chiamata bosone di Goldstone. della teoria si parte infatti da un’espressione della lagrangiana Oggi conosciamo la teoria dell’interazione forte che lega i in cui le masse sia dei fermioni sia dei bosoni vettori sono quark, che non esistono liberi, a formare gli adroni. Queste nulle. Il meccanismo che “genera” le masse fu scoperto da sono le particelle osservate sperimentalmente. Come già Peter Higgs [17] e da Robert Brout e François Engrlet [18] osservato, le masse dei quark che costituiscono la materia nel 1964. Il bosone scalare di Goldstone corrispondente è ordinaria sono piccolissime, dell’ordine del per cento delle chiamato particella di Higgs. Esso rimane ad oggi ipotetico, masse del protone e del neutrone. Le interazioni forti sono ma ce si ne aspetta la scoperta al nuovo collisore LHC del invarianti sotto la simmetria SU(3) dei sapori (u, d, s), che è CERN. rotta dalle differenze tra le masse dei quark. Nel limite in cui le masse dei quark si annullano, la lagrangiana si può esprimere come somma di due termini uguali, che coinvolgono 5 Mescolamento dei quark e violazione di CP rispettivamente quark “left” e quark “right”, ciascuno Quando si scoprì che le interazioni deboli violano sia la invariante sotto un gruppo SU(3). La simmetria complessiva parità sia la coniugazione particella-antiparticella, Lev è quindi SU(3) × SU(3). Questa, chiamata simmetria chirale, è Landau osservò nel 1957 [19] che tutti i dati disponibili erano però rotta sia esplicitamente, dalle masse non nulle dei quark, compatibili con l’invarianza sotto l’operazione congiunta CP, sia spontaneamente, dall’asimmetria del vuoto (dei sistemi cioè per inversione di parità accompagnata dalla sostituzione adronici). di tutte le particelle del sistema con le loro antiparticelle. Quando Nambu affrontò il problema non esistevano La simmetria, in una nuova forma, sembrava essere stata ancora né il concetto di quark né tanto meno la teoria della ripristinata. Tuttavia nel 1964 Christenson, Cronin, Fitch e cromodinamica quantistica. Ciò nonostante, egli comprese Turlay [20] scoprirono che anche la simmetria CP è violata, a che il pione è il bosone di Goldstone che corrisponde alla livello dei per mille, nei decadimenti dei mesoni K0. rottura spontanea appena menzionata. Come tale, se non ci Il contributo di Kobayashi e Maskawa è la scoperta fosse anche la rottura esplicita, la sua massa dovrebbe essere dell’origine della violazione in un coefficiente di fase presente nulla. Sappiamo oggi che il quadrato della massa del pione nella matrice di mescolamento dei quark. Prima di discuterlo è proporzionale alla somma delle masse dei quark che lo è necessario quindi riprendere il mescolamento dei quark. compongono, e quindi è molto piccola, qualche per cento Una conseguenza immediata_ della teoria di Cabibbo è la della massa del protone al quadrato. Si noti che Nambu aveva presenza del termine d’ g d ’ che descrive una corrente L m L _ _ g g anticipato così che il pione è una particella composta. “neutra”. Esso contiene le correnti neutre d L msL e s L mdL. Nambu fu in grado di giustificare, tra l’altro, una relazione Queste indurrebbero transizioni tra adroni con la stessa carica fenomenologia, trovata da Goldberger e Trieman [15], elettrica e diversa stranezza, transizioni che però non esistono tra la costante di accoppiamento assiale, la costante di o, meglio, sono molto fortemente soppresse. decadimento del pione e la forza dell’accoppiamento del La soluzione del problema fu trovata nel 1970 da Sheldon pione al nucleone. Glashow, John Iliopoulos e Luciano Maiani (“GIM”)[21], che Osserviamo ancora che se la simmetria fosse esatta, nello mostrarono che se ci fosse stato un quarto quark, di carica

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2/3, che fu chiamato charm, c, allora, oltre alla (4) ci sarebbe anni il lavoro sia sperimentale sia teorico in Giappone e anche la combinazione ad essa ortogonale in Occidente procedevano, in buona misura, per strade separate, senza l’interazione reciproca dei nostri giorni. (5) La fisica teorica giapponese fu in quel periodo fortemente _ _ influenzata dal modello introdotto da Sakata nel 1956 che ho g g Quindi , oltre al termine d’L mdL’, ci sarebbe anche s L’ msL’. Si già menzionato. Un contributo importante fu dato nel 1959 vede_ facilmente_ che nella somma dei due le correnti neutre da Gamba, Marshak e Okubo [28] che assunsero a ipotesi g g d L msL e s L mdL si cancellano. Gli autori ipotizzarono che il fondamentale la simmetria tra leptoni e barioni: i tre leptoni, quarto quark avesse massa notevolmente maggiore di quella ν, e, µ e i barioni p, n e Λ . dei quark noti, attorno ai 2 GeV. L’idea fu ulteriormente sviluppata l’anno successivo da Le due relazioni (4) e (5) indicano che nelle correnti deboli Ziro Maki, Masami Nakagawa, Yoshio Ohnuki e Shoischi adroniche cariche non compare la coppia di quark di tipo Sakata [29]. Nel loro modello, che prese il nome di modello down ma la coppia “ruotata” dell’angolo di Cabibbo di Nagoya, dall’università dove lavoravano, i leptoni sono particelle semplici, mentre i tre barioni fondamentali sono + (6) composti dalla “materia B ”, che ha numero barionico e carica elettrica positiva e da un leptone. Essi sono cioè

Nel novembre del 1974 due esperimenti indipendenti, un (7) doppio spettrometro magnetico per elettroni all’acceleratore di protoni AGS a Brookhaven [22] e MARK1 al collisore e+e– Il modello aveva molti lati positivi, ma non è quello realizzato SPEAR di SLAC [23], osservarono una risonanza estremamente in natura. In Giappone però sopravvisse per parecchi anni. stretta di massa di circa 3.1 GeV, chiamata J dal primo e ψ dal Quando però nel 1962 fu scoperto il secondo neutrino, la secondo. Essa fu immediatamente interpretata come stato simmetria tra barioni e leptoni sembrava persa. Due gruppi legato di un quark charm e del suo anti-quark. Il modello GIM teorici, uno di Kyoto composto da Y. Katayama, K. Matunoto, veniva confermato sperimentalmente. S. Tanaka e E. Yamada [30], e uno di Nagoya composto Il quark charm veniva a completare la seconda “famiglia” da Z. Maki M. Nakagawa e S. Sakata [31] avanzarono, per

assieme al quark strano, al leptone µ e al suo neutrino νµ recuperarla, la proposta che i neutrini fossero mescolati. Si che era stato scoperto all’acceleratore di Brookhaven nel noti che questo avvenne prima ancora che si sapesse dei 1962 da G. Damby et al. [24]. Si noti che il mescolamento dei quark, e ancor meno ovviamente del loro mescolamento. I quark può essere espresso indifferentemente o per i quark di neutrini “veri” sono cioè tipo down o per quelli di tipo up. Si usa la prima alternativa perché, storicamente, quando il mescolamento fu introdotto (8) erano noti due quark di tipo down ed uno solo di tipo up. Da un punto di vista teorico non c’erano ragioni per e solo il primo di questi si accoppia alla materia B+ immaginare quark e leptoni al di là di quelli noti. Tuttavia già nel 1967 Antonino Zichichi aveva ipotizzato l’esistenza di (9) un terzo leptone, che chiamò Heavy Lepton (HL), e del suo ν neutrino HL. Zichichi e i suoi collaboratori progettarono e Né un gruppo né l’altro danno giustificazione alcuna n + costruirono il necessario apparato sperimentale ad ADONE a dell’assenza del barione 2B . Se però ci fosse, ipotizzano, Frascati [25], l’anello di accumulazione e+e– di energia più alta allora ci sarebbe un quarto barione fondamentale, che disponibile allora. La reazione complessiva cercata era il gruppo di Kyoto chiama V, con un nuovo sapore, T. È e+e– → e+m–, che, per non violare i numeri leptonici, avrebbe un’ipotesi analoga a quella del charm, ma motivata da ben + – dovuto procedere tramite uno stato intermedio HL_ HL altre considerazioni. + +n - m-n seguito dai decadimenti HL → e e e HL → m. La Per entrambi i gruppi, le correnti deboli adroniche devono massa di HL, ora chiamato τ, è però troppo grande per essere riprodurre, per la simmetria tra barioni e leptoni, le correnti prodotto ad ADONE e Zichichi e collaboratori poterono leptoniche. La corrente barionica dovrà quindi essere [31] solo mettervi dei limiti [26]. Quando un collisore con l’energia sufficiente, SPEAR a Stanford, divenne disponibile, (10) il leptone fu scoperto, con lo stesso metodo, da Martin Perl e collaboratori [27]. Gli autori notano che questa espressione è identica alla È opportuno ora discutere gli sviluppi della fisica delle modifica della corrente barionica suggerita da Gell-Mann e particelle elementari in Giappone negli anni 1960. In quegli Levy [12], aggiungendo che essa trova nel modello di Nagoya

100 < il nuovo saggiatore a. bettini: il premio nobel per la fisica 2008

una giustificazione. Sappiamo oggi che sia i neutrini sia i Dopo la scoperta di Niu, i gruppi sperimentali giapponesi quark sono mescolati, ma con angoli di mescolamento grandi cercarono attivamente eventi simili in esposizioni di per i primi, piccoli per i secondi. camere ad emulsioni ad alta quota. Nel 1974, l’anno della Un fatto ancora oggi poco noto in Occidente è che la scoperta della J/ψ, si erano trovati 20 decadimenti, che scoperta del charm avvenne in realtà nel 1971, tre anni prima furono presentati l’anno successivo alla 14a Conferenza di quella della J/ψ, da parte di Kiyoshi Niu [32], allora a Tokyo Internazionale sui Raggi Cosmici a Monaco [35]. Essi avevano e successivamente a Nagoya. In quegli anni in Giappone tutte le caratteristiche previste per il charm. i raggi cosmici venivano ancora impiegati nella ricerca di È chiaro quindi che il gruppo teorico di Nagoya nel 1971 era frontiera, mentre in Occidente si lavorava agli acceleratori. Era convinto dell’esistenza di un quarto barione fondamentale. questa una conseguenza degli scarsi investimenti in ricerca Ciò favorì in loro l’idea che ce ne potessero essere altri. di base. L’ovvio svantaggio è che non è possibile controllare i Nel 1972 Kobayashi e Maskawa [36] indagarono sulla raggi cosmici primari. Tuttavia essi potevano produrre eventi, possibilità di trovare una spiegazione della violazione di CP con probabilità ragionevoli, ad energie, anche di parecchi TeV, nell’ambito della teoria delle interazioni deboli. Ragionavano allora non disponibili agli acceleratori. A questo scopo Niu e nel modello di Nagoya, cioè i barioni invece dei quark come collaboratori avevano realizzato grandi progressi nella tecnica particelle fondamentali. Una prima conclusione della loro delle emulsioni nucleari, costruendo rivelatori, le “Emulsion analisi fu che ciò non era possibile con solo i quattro noti. Era Chamber”, composti da “sandwich” di emulsioni e materiale necessario introdurre nuovi campi. Discussero due possibilità: plastico trasparente e di ottime proprietà ottiche per il un campo scalare o sei barioni in totale (cioè sei quark). tracciamento delle particelle cariche e di emulsioni e piombo La matematica della seconda possibilità, tradotta in termini di per la misura dell’energia dei gamma, e quindi dei π0. quark, è semplice. La matrice di mescolamento è una matrice In un’esposizione in un volo ad alta quota, Niu e collaboratori unitaria. Se ci sono quattro quark, e quindi due di tipo down osservarono un evento straordinario. Esso mostrava al di là che si mescolano, la matrice è 2 × 2 e ha 4 elementi reali di ogni dubbio la produzione associata, tramite interazione indipendenti. Si dimostra che tre di questi sono fattori di fase. forte, di due particelle instabili, che decadevano in tempi di Essi possono essere eliminati ridefinendo le funzioni d’onda. una frazione di picosecondo, e quindi per interazione debole. La matrice rimanente è reale, la rotazione in un piano, di L’analisi dell’evento permise di determinare la massa di una Cabibbo. delle due particelle. A seconda che la particella carica del Se ci sono 6 quark, e quindi tre di tipo down che si mescolano, suo decadimento fosse un pione o un protone, la particella la matrice è 3 × 3 e ha 9 elementi reali indipendenti. Tre di poteva essere un mesone di massa 1.8 GeV o un barione questi si possono considerare come gli angoli di Eulero di una di massa 2.9 GeV, con incertezze del 30%. Non poteva rotazione degli assi in tre dimensioni (uno di questi è l’angolo quindi essere una particella strana. Niu aveva scoperto un di Cabibbo). Gli altri 6 sono fattori complessi di fase. Se ne uovo tipo di adrone. Era il charm, con la massa prevista da possono eliminare 5 ridefinendo le funzioni d’onda. Ma uno Glashow, Iliopoulos e Maiani, ma fu chiamato X. La scoperta rimane. E tanto basta per avere violazione di CP. fu presentata alla 12a Conferenza Internazionale sui Raggi L’estensione a sei quark della teoria di Cabibbo completata Cosmici nel 1971 e sulla rivista giapponese “Progress of col quarto quark di Glashow, Iliopoulos e Maiani, forniva Theoretical Physics” [32]. quindi un’interpretazione della violazione di CP osservata nei Immediatamente dopo la scoperta, S. Ogawa che guidava il mesoni K0. ramo di Hiroshima della scuola di pensiero di Sakata, mise in Il quinto quark fu scoperto in uno stato legato quark- evidenza che la nuova particella poteva contenere un quarto antiquark nel 1977 [37], il sesto dall’esperimento CDF al tipo di quark [33], che avrebbe potuto essere il charm. Il Tevatron nel 1995 [38]. lavoro giunse a “Progress of Theoretical Physics” nell’agosto La violazione di CP fu studiata nei dettagli, oltre che nei del 1971, ma fu pubblicato dopo qualche mese. decadimenti dei K0, anche in quelli dei mesoni B0. A questo Riuscì invece ad essere pubblicato immediatamente fine furono costruiti due collisorie +e– ad alta luminosità di seguito a quello di Niu un altro articolo teorico di operanti_ all’energia ideale per la produzione di coppie interpretazione, di Ziro Maki e Toshihide Maskawa [34] di B0 B 0, uno, PEP2 a SLAC in California, l’altro, KEKB, a KEK in Nagoya. Essi ricordano che storicamente “il concetto di un Giappone. Entrarono in funzione nel 1999 con gli esperimenti quarto barione fondamentale fu introdotto nel 1962 dai BABAR [39], con grande partecipazione italiana, e BELLE [40]. gruppi di Nagoya e di Kyoto”, come abbiamo già menzionato. Fornirono una serie di test di alta precisione che mostrano, Osservano che siffatta estensione del modello di Nagoya con almeno sinora, perfetto accordo con il Modello Standard e, simmetria leptoni-barioni a quattro barioni fondamentali in particolare, con la matrice di mescolamento di Cabibbo, fornisce una naturale interpretazione dell’evento di Niu. Kobayashi e Maskawa. Tuttavia essi non menzionano il charm.

vol24 / no5-6 / anno2008 > 101 Bibliografia [20] J. H. Christenson et al., “Evidence for the two π decay of the meson”, Phys. Rev. Lett., 13 (1964) 138. [1] The Royal Swedish Academy of Sciences, “Broken Symmetries, [21] S. L. Glashow, J. Iliopoulos e L. Maiani, “Weak interactions with Scientific background on the Nobel Prize in Physics 2008”, 7 October lepton-hadron symmetry”, Phys. Rev. D, 2 (1970) 1285. 2008. [22] J. J. Aubert et al., “Experimental observation of a heavy particle J”, [2] H. Poincaré, “Sur la dynamique de l’électron”, Acad. Sci. Paris, 140 Phys. Rev. Lett., 33 (1974) 1404. (1905) 1504; Rendiconti del Circolo Matematico di Palermo, 21 [23] J. F. Augustin et al., “Discovery of a narrow resonance in e+e– (1906) 494. annihilation”, Phys. Rev. Lett., 33 (1974) 1406. [3] E. Noether, “Invariante Variationprobleme”, Nachr. d. Koenig. [24] G. Damby et al., “Observation of high-energy neutrino reactions and Gessellschaft d. Wiss. zu Göttingen (1918) 235. the existence of two kinds of neutrinos”, Phys. Rev. Lett., 9 (1962) 36. [4] W. Heisenberg, “Über de Bau der Atomkerne I”, Z. Phys., 77 (1932) 1. [25] M. Bernardini et al., “A proposal to search for leptonic quarks and [5] S. Sakata, “On a composite model for the new particles”, Progr. Theor. heavy leptons produced at ADONE”, INFN/AE-67/3 (1967), non Phys., 16 (1956) 686. pubblicato. [6] M. Gell-Mann, “The eightfold way: a theory of strong interaction [26] V. Alles-Borelli et al., “Limits on the electromagnetic production of symmetry”, (1961), non pubblicato. heavy leptons”, Lett. Nuovo Cimento, 4 (1970) 1156; M. Bernardini [7] Y. Ne’eman, “Derivation of strong interactions from gauge et al., “Limits on the mass of heavy leptons”, Il Nuovo Cimento A, 17 invariance”, Nucl. Phys., 26 (1961) 222. (1973) 383. [8] G. Zweig, “An SU(3) model for strong interaction symmetry and its [27] M. L. Perl et al., “Evidence for anomalous lepton production in breaking”, CERN Report 8419/TH 412 (1964), non pubblicato. e+e– annihilation”, Phys. Rev. Lett., 35 (1975) 1489. [9] M. Gell-Mann, “A schematic model of baryons and mesons”, Phys. [28] A. Gamba, R. E. Marshak e S. Okubo, Proc. Natl. Acad. Sci. U.S.A., 45 Lett., 8 (1964) 214. (1959) 881. [10] M. Breindenbach et al. “Observed behaviour of highly inelastic [29] Z. Maki, M. Nakagawa, Y. Ohnuki e S. Sakata, “A unified model for electron-proton scattering”, Phys. Rev. Lett., 23 (1969) 935. elementary particles”, Progr. Theor. Phys., 23 (1960) 1174. [11] N. Cabibbo, “Unitary symmetry and leptonic decays”, Phys Rev. Lett., [30] Y. Katayama, K. Matunoto, S. Tanaka e E. Yamada, “Possible unified 10 (1963) 531. models of elementary particles with two neutrinos”, Progr. Theor. [12] M. Gell-Mann e M. Levy, “The axial vector current in the theory of Phys., 28 (1962) 675. beta decay”, Il Nuovo Cimento, 16 (1960) 705. [31] Z. Maki. M. Nakagawa e S. Sakata, “Remarks on the unified model of [13] Y. Nambu, “A superconductor model of elementary particles elementary particles”, Progr. Theor. Phys., 28 (1962) 870. and its consequences”, Lezione a Purdue (1960), in “Broken [32] K. Niu, E. Mikumo e Y. Maeda, “A possible decay in flight of a new symmetries. Selected papers by Y. Nambu”, a cura di T. Educhi e K. type of particle”, Progr. Theor. Phys., 46 (1971) 1644. Nishijima (World scientific) 1955; Y. Nambu e G. Iona-Lasinio, “A [33] T. Hayashi et al., “A possible interpretation of the new event in the dynamical model of elementary particles based on an analogy with cosmic ray experiment”, Progr. Theor. Phys., 47 (1972) 280. superconductivity”, Phys. Rev. B, 122 (1961) 345; 124 (1961) 246; Y. [34] Z. Maki e T. Maskawa. “Fundamental quartets and chiral U(4)×U(4)”, Nambu e D. Lurié, “Chirality conservation and soft pion production”, Progr. Theor. Phys., 46 (1971) 1647. Phys. Rev., 125 (1962) 862; Y. Nambu e [35] K. Hoshino et al., Proceedings of the 14th International Cosmic Rays E. Shrauner, “Soft pion emission induced by electromagnetic and Conference, 7 (1975) 2442. weak interactions”, Phys. Rev., 128 (1962) 862. [36] M. Kobayashi e T. Maskawa, “CP-violation in the renormalizable [14] J. Goldstone, “Field theories with superconductor solutions”, Il Nuovo theory of weak interactions”, Progr. Theor. Phys., 49 (1972) 652. Cimento, 19 (1961) 154. [37] S. W. Herb et al., “Observation of a dimuon resonance at 9.5 GeV in [15] M. L. Goldberger e S. B. Trieman, “Decay of the π meson”, Phys. Rev,. 400 GeV proton-nucleus collisions”, Phys. Rev. Lett., 39 (1977) 252. 110 (1958) 1178. [38] T. Abe et al., “Observation of top quark production in collisions”, [16] A. Bettini et al., “Evidence for a strong, possibly resonant, scalar ρρ Phys. Rev. Lett., 74 (1995) 263. interaction”, Il Nuovo Cimento, 42 (1968) 695. [39] B. Aubert et al., “Measurement of the CP-violating Asymmetry [17] P. W. Higgs, “Broken symmetries an the mass of the gauge bosons”, Amplitude sin 2β”, Phys. Rev. Lett., 89 (2002) 201802. Phys. Rev. Lett,. 13 (1964) 508. [40] K. Abe et al. “An Improved Measurement of Mixing-induced CP [18] F. Englert e R. Brout, “Broken symmetries and the mass of the gauge violation in the Neutral B Meson System”, Phys. Rev. D, 66 (2002) vector bosons”, Phys. Rev. Lett., 13 (1964) 321. 071102. [19] L. D. Landau, “On the conservation laws for weak interactions”, Nucl. Phys,. 3 (1957) 127.

Alessandro Bettini Professore ordinario di Fisica Generale presso l’Università di Padova dal 1981, ha ricoperto incarichi di responsabilità nell’INFN dal 1978 al 2003, come Presidente della seconda Commissione Scientifica Nazionale, Direttore della Sezione di Padova, Membro della Giunta Esecutiva, Vicepresidente dell’Istituto, e Direttore del Laboratorio Nazionale del Gran Sasso. È stato membro del Super-Proton-Syncroton Committee del CERN (1987-89) e di ECFA (1997-2003), vice-presidente del Mega Science Forum (1996-98) e del Global Science Forum dell’OCSE dal 1999, Presidente del Particle and Nuclear Astrophysics and Gravitation International Committee della IUPAP (1998-2005). Dal 2008 è Direttore del Laboratorio Sotterraneo di Canfranc (Spagna). Fisico sperimentale di particelle elementari ha condotto e diretto esperimenti presso il CERN e LNGS. Ha dato contributi alla spettroscopia degli adroni, in particolare con la scoperta della prima risonanza scalare, allo studio delle annichilazioni di antiprotoni, alla fisica del charm, dei bosoni vettori e del neutrino. È autore o coautore di più di 150 pubblicazioni scientifiche su riviste internazionali con referendari, di tre volumi di fisica generale pubblicati da Zanichelli e di uno di particelle elementari pubblicato da Cambridge University Press. È socio dell’Accademia Galileiana di Scienze Lettere e Arti e della Società Italiana di Fisica, di cui è consigliere.

102 < il nuovo saggiatore il nostro mondo

Torino ospiterà dal 2 al 7 luglio 2010, nella splendida cornice di Torino ma dell’Italia su un prestigioso palcoscenico del Lingotto, la prossima edizione di ESOF – Euroscience scientifico internazionale e per il rilancio di una cultura, quella Open Forum, diventando Città Europea della Scienza (www. scientifica, il cui valore strategico e la cui necessità sono ormai esof2010.org). riconosciuti universalmente. ESOF è un meeting europeo biennale, dedicato alla ricerca Speriamo quindi in una forte risposta della comunità e all’innovazione scientifica ideato da Euroscience www.( scientifica e culturale italiana con proposte innovative e di euroscience.org), organizzazione che riunisce membri di qualità alla call for proposals che sarà aperta da dicembre 40 Paesi europei. 2008 e un’ampia partecipazione a ESOF2010 a Torino. ESOF coinvolge scienziati di tutte le discipline, ricercatori del ESOF2010 è organizzato dall’Associazione TopESOF settore pubblico e privato, insegnanti e studenti, esponenti – Torino per ESOF2010 costituita da Centro Agorà Scienza del mondo politico ed industriale, appassionati di scienza, dell’Università di Torino, Compagnia di San Paolo e operatori dei mezzi di comunicazione e semplici cittadini. Centroscienza Onlus. È un’occasione di incontro unica in Europa 1) per presentare La prima edizione di ESOF si è svolta nel 2004 a Stoccolma e discutere le frontiere della ricerca scientifica e tecnologica, (www.esof2004.org), mentre quella del 2006 è stata la relazione tra scienza e società e le politiche a sostegno ospitata da Monaco di Baviera (www.esof2006.org). della ricerca scientifica Conference( Programme), 2) per La terza edizione si è svolta a Barcellona dal 18 al 22 luglio sviluppare programmi mirati ai giovani (Career Programme), 2008 ed è stata un grande successo di pubblico: ha visto 3) per iniziative rivolte al grande pubblico di diffusione della l’adesione di circa 5000 partecipanti alla sola conferenza, cultura scientifica (“Science in the City” Programme), 4) per raddoppiati rispetto all’edizione del 2006. interagire con il mondo in diretta free streaming (webESOF Anche la presenza dei media è cresciuta rispetto all’edizione Programme). precedente, circa 600 erano quelli presenti nei giorni del La selezione della città che organizza ESOF avviene da parte Forum, a testimonianza di un sempre maggior interesse verso di Euroscience sulla base dei dossier presentati dalle città ESOF, diventato un appuntamento imperdibile nel panorama che partecipano alla gara di assegnazione. La candidatura scientifico europeo. di Torino ha vinto la durissima competizione con Parigi, ESOF2008 è stata un’importante opportunità per presentare Copenhagen e Breslavia ed è con grande orgoglio che alla comunità internazionale presente a Barcellona l’edizione abbiamo ottenuto un successo che contiamo si trasformi 2010 di ESOF, che verrà ospitata a Torino. in un momento importante per la presentazione non solo Uno degli obiettivi principali di ESOF è quello di contribuire ad avvicinare i giovani alla scienza, una delle prime azioni di coinvolgimento promosse da TopESOF è stata proprio rivolta 1 a loro. Il 30 aprile 2008 è stato bandito in collaborazione con La Stampa il concorso “Prendi il bus della scienza: destinazione Barcellona”, riservato agli studenti dei primi due anni di un’Università piemontese. I 40 vincitori del concorso (vedi fig. )1 hanno avuto l’opportunità di vincere un viaggio a Barcellona per partecipare a ESOF2008, seguendo le conferenze in programma ed essendo coinvolti nelle attività che ESOF2010 ha organizzato durante ESOF2008. I 40 ragazzi hanno contribuito a dare una forte visibilità a ESOF2010, offrendosi fra l’altro di far compilare il questionario, presente anche on line sul sito di ESOF2010, redatto allo scopo di raccogliere suggerimenti e consigli per

vol24 / no5-6 / anno2008 > 103 la prossima edizione di ESOF a Torino. 2 I partecipanti di ESOF2008 hanno avuto la possibilità di compilare il questionario anche all’interno dello stand di ESOF2010, più di 400 persone hanno lasciato i loro suggerimenti. Lo stand di ESOF2010 (fig. )2 ha raccolto numerosi consensi tra i visitatori e gli addetti ai lavori: l’uso di colori brillanti, di cubotti colorati che richiamano lo slogan di ESOF2010 “Passion for Science”, che a sua volta si ispira alla tavola degli elementi di Mendeleev, la costante presenza dei 40 ragazzi vincitori del concorso ad animare lo stand, lo ha reso uno dei più visitati dal pubblico. ESOF2010, attraverso il suo stand, ha dato un arrivederci a Torino 2010 e ha confermato l’immagine radicata nella sua storia di una città-laboratorio aperta alla ricerca e all’innovazione scientifica. Sul sito è inoltre possibile iscriversi alla newsletter di I prossimi appuntamenti: ESOF2010 per ricevere regolarmente aggiornamenti Entro il mese di dicembre 2008 saranno pubblicati sul sito sull’evento. www.esof2010.org i temi dell’edizione 2010 di ESOF e la call for proposals per le sessioni del Conference Programme, per le attività del “Science in the City” Programme e del Enrico Predazzi, Andrea De Bortoli Career Programme. Centro Agorà Scienza - Università di Torino

Nell’ambito del programma di“La Fête de Science en France” e nel quadro della comunicazione al grande pubblico dell’ esperimento ALICE, è stata rappresentata al CERN nel Globe de la Science et de l’Innovation la realizzazione teatrale di Marco Monteno “Arlequin et la couleur des quarks”. Si tratta di una favola poetica e divertente che invita a entrare nell’universo della fisica quantistica e dell’esperimento ALICE. L’autore è un ricercatore dell’INFN di Torino, si occupa di fisica nucleare delle alte energie e collabora con ALICE, un esperimento che studia le collisioni di ioni pesanti a LHC, allo scopo di rivelare uno stato della materia primordiale denominato plasma di quark e di gluoni.

104 < il nuovo saggiatore il nostro mondo premio sergio fubini 2008

Il Premio Sergio Fubini è stato istituito dall’INFN per premiare le tre migliori tesi di dottorato del 2007-2008. I vincitori hanno ottenuto il premio in una cerimonia, presso la presidenza INFN, da parte del presidente INFN in presenza della Commissione scientifica teorica dell’INFN.

Sergio Fubini è stato un grande fisico teorico. La sua visione d’insieme che ha portato a varie pubblicazioni. Nella disamina delle tesi ha tenuto lo ha portato a molte applicazioni di modelli teorici. Negli anni 1960 conto, oltre alla chiarezza della presentazione, ai risultati scientifici e al ha dato una base a concetti di matrice S come le singolatità di Regge. potenziale di sviluppo della ricerca nel settore. Le tre tesi giudicate le Successivamente ha fornito una formulazione algebrica alla algebra migliori per il Premio INFN Sergio Fubini 2008 sono, in ordine alfabetico delle correnti che ha giocato un ruolo importante per la nascita del di autore: modello duale. Quindi Fubini ha fattorizzato, insieme a Veneziano, la − Dr. Giuseppe Florio, Decoherence and entanglement in quantum matrice S del modello di Veneziano convergendo verso una teoria di information processing campo con infinite componenti aprendo cosi la strada a quello che − Dr. Stefano Gandolfi,The auxiliary field diffusion Monte Carlo method for sarebbe diventata la teoria delle corde (o stringhe). Ovunque abbia nuclear physics and nuclear astrophysics lavorato, Fubini ha lasciato un profondo segno sugli studenti e sulle − Dr. Salvatore Mansi, Geometric aspects of N=2 supergravity istituzioni come le Università di Torino e Padova, in Italia, e su MIT e La premiazione è avvenuta a Roma il 22 settembre 2008 presso la CERN. Presidenza INFN in occasione della riunione della Commissione Il Premio Sergio Fubini 2008 è stato indetto dalla Presidenza INFN come scientifica teorica dell’INFN. Il Premio è stato consegnato dal Prof. riconoscimento di possibili tre migliori tesi di dottorato discusse nel Roberto Petronzio, presidente dell’INFN, dopo i seminari dei vincitori. periodo dal 15 aprile 2007 al 15 aprile 2008 su argomenti di interesse Il Premio annuale Sergio Fubini, istituito dalla Commissione scientifica della Commissione scientifica teorica dell’INFN (fisica teorica in senso teorica INFN nel 2005, è diventato un Premio dell’INFN dallo scorso lato). Ogni anno vi sono oltre 70 tesi di dottorato nel settore. Il vincitore anno. Successivamente l’INFN ha istituito altri Premi annuali per le linee ottiene un attestato e un premio di 2000,00 euro. La selezione delle tesi di ricerca sperimentali. migliori è stata fatta da una Commissione formata nel 2008 da Silvia Penati (presidente), Marco Radici, e Massimo Pietroni (segretario). La Commissione, che per alcune tesi si è avvalsa di referee esterni, ha Giuseppe Marchesini ricevuto varie proposte di cui ha sottolineato l’elevato livello scientifico Università di Milano-Bicocca e INFN

Progetto Lauree Scientifiche: Borse SIF

Come già fatto nell’anno accademico 2006-2007, la SIF – Società normalmente svolti nella maggioranza degli Istituti di Istruzione Italiana di Fisica – d’intesa con il MIUR, nell’ambito del progetto “Lauree Secondaria Superiore; sono stati formulati in modo da permettere ai Scientifiche”, ha assegnato 42 borse di studio, del valore di 4000 euro, a concorrenti di potersi confrontare non solo su un bagaglio comune di studenti che si sono immatricolati nell’anno accademico 2008-2009 ad conoscenze indipendente dal particolare corso di studi frequentato un corso di Laurea della Classe di “Scienze e Tecnologie Fisiche” – Classe ma anche sulla capacità individuale di sviluppare un ragionamento 25 DM509 e Classe L-30 DM270. L’assegnazione è avvenuta, a seguito di scientifico. una selezione su base nazionale, effettuata attraverso una prova scritta Relativamente al questionario, allo scopo di penalizzare, in media, la diretta a verificare le conoscenze scientifiche, con particolare riferimento strategia della risposta casuale per i quesiti di cui non si conosce quella alla Fisica. esatta, la Commissione ha attribuito i seguenti punteggi: Le borse sono annuali e rinnovabili di anno in anno per tutta la durata › 0 per la risposta non data del corso triennale di studi a condizione di aver superato tutti gli esami › 0.75 per la risposta esatta previsti per l’anno di fruizione della borsa e per gli anni precedenti › -0.25 per la risposta sbagliata entro il 31 dicembre con la media, pesata con i crediti relativi agli Il numero di idonei, cioè di concorrenti con un punteggio maggiore insegnamenti, di almeno 27/30 e voto minimo di almeno 24/30. o uguale al 75% del punteggio massimo conseguibile (che era di I partecipanti al concorso sono stati 486 su 603 che avevano presentato 26.25), è stato di 123. Il sovrapporsi con l’elenco di vincitori alla Scuola la domanda. Superiore di Catania e all’Università degli Studi di Milano Bicocca ha La selezione per determinare i vincitori delle 42 borse si è svolta il determinato due rinunce allungando la classifica dei vincitori fino al 15 Ottobre 2008 contemporaneamente nelle varie Sedi universitarie quarantaquattresimo classificato della graduatoria degli idonei il cui italiane in cui era presente un corso di Laurea delle sopra citate classi. punteggio è stato di 22.00. La prova scritta è durata 3 ore e si è articolata in 35 quesiti a risposta A tutt’oggi, l’86% dei vincitori delle borse vinte nella selezione dell’anno multipla, con una sola risposta esatta tra le quattro indicate. accademico 2006-2007 ha ottenuto la proroga a testimonianza della Le fasi di preparazione e di correzione degli elaborati si sono validità e della selezione effettuata e dello stimolo, fornito ai più svolte a Bologna presso la sede della SIF e sono state curate da meritevoli, a proseguire con regolarità i propri studi universitari. una Commissione, nominata il 21 Settembre 2008 dal Consiglio di Il bando del suddetto concorso, i 35 quesiti e le rispettive soluzioni, le Presidenza della Società Italiana di Fisica e composta da Vincenzo Grasso graduatorie degli idonei e dei vincitori, sono disponibili all’indirizzo (Presidente), Anna Cavallini, Josette Imme’, Letteria Silipigni e Rosa Maria http://www.sif.it Sperandeo Mineo. I 35 quesiti, sorteggiati tra quelli proposti da ogni Commissario, Vincenzo Grasso hanno riguardato argomenti di Fisica, Chimica, Matematica e Logica Università di Messina

vol24 / no5-6 / anno2008 > 105 il nostro in ricordo di mondo

Frederick Seitz e amicizia con molti illustri fisici della sua epoca, in Solido negli anni ‘50-‘60 . particolare con alcuni dei fisici italiani che si erano Passiamo ora a descrivere sommariamente alcuni rifugiati negli Stati uniti per sfuggire alle leggi risultati scientifici di grande rilievo ottenuti dal razziali del 1938 (2). Seitz nella sua lunga carriera. Egli per primo ha Egli non riusciva tuttavia a capacitarsi del perché applicato le proprietà dei gruppi spaziali alla in quel periodo la Fisica in Italia si presentasse classificazione degli stati quantici dei cristalli unicamente come Fisica delle particelle elementari ricavando principi di validità generale sulla e in parte come Fisica nucleare, rinunciando a sequenza dei livelli elettronici e sviluppando contribuire al vertiginoso sviluppo della tecnologia il formalismo matematico di base. Con E. P. e dell’elettronica a stato solido che si ebbe in Wigner (il suo maestro a Princeton) ha applicato seguito all’invenzione del transistor (1948) e concretamente per primo il concetto delle bande del transistor a giunzione (1949). Nel 1960 fu di energia sviluppando un metodo per calcolarle sviluppato il MOS (transistor ad effetto campo a (in seguito chiamato di Wigner e Seitz), che è struttura planare) che ha costituito la base per i diventato il fondamento di tutti i metodi moderni circuiti integrati. Nel 1954 fu inoltre inventato il per il calcolo della struttura a bande. In tal modo MASER e nel 1958 il LASER (nel 1960 evoluto nel ha risolto il problema della coesione dei metalli, laser a semiconduttore che poi ha dato origine, tra un problema che non era risolubile con la teoria l’altro, agli ubiqui LED ). Ma anche in altri aspetti del legame chimico né con la teoria degli elettroni Il due marzo scorso è morto Frederick Seitz, fondamentali della Fisica dello Stato Solido il indipendenti a causa dell’importanza degli effetti fondatore della moderna Fisica dello Stato contributo italiano in quel periodo era pressoché di correlazione. Solido. Riteniamo utile ancorché doveroso inesistente. Un altro settore cui il Seitz ha contribuito in ricordare brevemente le sue attività scientifiche e Nel 1957 la teoria BCS della superconduttività maniera rilevante è quello dell’interazione organizzative, connesse con lo sviluppo della Fisica aveva spiegato un fenomeno che aveva resistito radiazione-materia sia nei cristalli perfetti con dei Solidi nell’Italia degli anni ’50-’60. ai tentativi di interpretazione dei più illustri le transizioni tra stati elettronici che negli stati Frederick Seitz era nato a San Francisco il 4 fisici teorici per quasi mezzo secolo e che poi di impurezza, contribuendo alla spiegazione del Luglio 1911. Era cresciuto in un quartiere ha permesso (tra le molte altre applicazioni) di fenomeno della fluorescenza. In questo contesto abitato prevalentemente da italo-americani di produrre campi magnetici di svariate decine di ha introdotto il cosiddetto metodo delle coordinate ascendenza ligure, chiamato infatti Nuova Liguria. Tesla. Un grande sviluppo aveva anche avuto lo configurazionali (una modellizzazione del teorema I suoi compagni di giochi erano figli di piccoli studio degli stati elettronici nei Solidi che aveva adiabatico) che attraverso l’accoppiamento degli commercianti o impiegati che costituivano la portato tra l’altro alla teoria e alla tecnologia dei stati elettronici con i modi vibrazionali spiega modesta borghesia di Nuova Liguria senza alcuna semiconduttori. la differenza di frequenza tra l’assorbimento e importanza sociale, politica o amministrativa nella Il Seitz, che aveva dato contributi importanti a l’emissione (Stoke’s shift) e le relative probabilità società californiana, all’epoca in prorompente tale teoria, aveva preconizzato questi sviluppi di transizione. Tale metodo gli ha consentito di sviluppo(1). e si domandava che cosa avrebbe potuto fare interpretare lo spettro di emissione degli alogenuri Fu forse questa contiguità di giochi e per “esportare” in Italia questo tipo di Fisica. alcalini drogati con tallio, che costituiscono una frequentazioni che suscitò nel giovane Frederick L’occasione gli si presentò con la comparsa del classe di materiali importanti per la rivelazione la curiosità di approfondire i rapporti tra la società giovane Fausto Fumi al Carnegie Institute of delle radiazioni. italo-americana e quella del loro paese di origine. Technology, di cui Seitz era direttore delle ricerche, Da segnalare sono anche i suoi contributi alla Nei primi anni del dopo-guerra, F. Seitz era già con una borsa Fullbright. Scrive F. Seitz (3): comprensione della struttura elettronica associata divenuto un fisico famoso che aveva contribuito “One must give very special recognition to Fausto for ai difetti reticolari e delle proprietà ottiche dei a fondare su basi quantomeccaniche la Fisica dei being the adventuresome Columbus of solid state centri di colore. Solidi. Il suo libro “Modern Theory of Solids”, apparso physics and coming essentially alone to the United Un aspetto rilevante della personalità del Seitz nel 1940, era stato per molti decenni la bibbia sulla States”. è stata la grande generosità che lo ha spinto a quale si erano formate generazioni di ricercatori. Fumi seguì Seitz all’Università dell’Illinois nel 1949, dedicare molto del suo tempo alla formazione Nel periodo bellico aveva lavorato al “Progetto prima di rientrare in Italia a Milano, stabilendo dei giovani e alla creazione di una scuola di Fisica Manhattan”, particolarmente allo sviluppo proficui contatti con l’Università di Pavia dove dei Solidi all’Università dell’Illinois, per molti metallurgico del silicio (allora usato per i rivelatori si trovavano gli (allora giovani) scriventi. F. Seitz anni un punto di riferimento a livello mondiale a cristallo per microonde, ma in seguito divenuto venne spesso in Italia in quegli anni, facendo in questo settore. F. Seitz ha avuto una messe il materiale elettivo per la moderna elettronica a conferenze e seminari, suggerendo esperimenti, di riconoscimenti che sarebbe troppo lungo stato solido). La vastità dei suoi interessi e la sua favorendo il soggiorno di ricercatori italiani nelle elencare, tra gli altri la Presidenza dell’Accademia capacità di coordinare attività molto diversificate lo Università americane, in particolare all’Università americana delle Scienze, la medaglia Franklin avevano portato a stabilire rapporti di familiarità dell’Illinois dove alcuni di noi hanno potuto (1965), la medaglia Compton (1970), il più ambito ricoprire posizioni di ricerca superiori a quelle che riconoscimento dell’Institute of Physics americano, e Lauree Honoris Causa da 32 Università. Ma il (1) ci competevano come giovani ricercatori. Unica eccezione, tuttavia di grande rilevanza, Nel 1957 F. Seitz collaborò all’organizzazione della più grande dei riconoscimenti è la stima dei suoi era costituita da Amedeo Pietro Giannini (San Josè prima Scuola italiana di Fisica dello Stato Solido a colleghi e l’affetto dei suoi allievi. Tutti quelli che lo 1870, San Mateo 1949), che aveva fondato nel 1904 Varenna (diretta da F. Fumi). Subito dopo ci fece hanno conosciuto, e gli scriventi in particolare, non la Bank of Italy, trasformata nel 1928 nella Bank of avere contratti con i Servizi Americani (AFOSR), dimenticheranno mai la sua grande bontà, il suo America, una delle più grandi banche commerciali sorriso da cui traspariva comprensione e simpatia, degli Stati Uniti, che ebbe un ruolo essenziale nello passaggi gratuiti per e da gli Stati Uniti, e in ogni le sue frasi semplici ma sempre dense di significato. sviluppo agricolo e industriale della California. caso un sostegno scientifico, psicologico e morale A lui abbiamo voluto bene come a un padre e un (2) che servì a superare le inevitabili difficoltà associate Tra gli altri: E. Fermi, E. Segrè, G. C. Wick, B. Rossi, all’inizio di una attività di ricerca in un settore per amico e il suo ricordo ci accompagnerà per il resto U. Fano, F. Rasetti. noi nuovo e molto diversificato. Insieme ad altri della nostra vita. (3) F. Seitz: “Reminescence of a half century of solid illustri scienziati che frequentarono in quegli anni state science with Italian links”, in: “The origin of Solid- le Università di Milano e Pavia – tra gli altri Sir Nevill Giuseppe Franco Bassani State Physics in Italy, 1945-1960”, a cura di G. Giuliani, Mott, J. Robert Schrieffer, Alfred Kastler, Jacques Scuola Normale Superiore, Pisa Società Italiana di Fisica, Atti di Conferenze, Vol.13 Friedel, Tom Morgan – ci fece sentire partecipi dello Gianfranco Chiarotti (Editrice Compositori, Bologna) 1987, p. 215. sviluppo che stava avendo la Fisica dello Stato Università di Roma “Tor Vergata”

106 < il nuovo saggiatore Venzo De Sabbata mai a scapito della fisica e dei metodi sperimentali problems” in solid state physics. This had required impiegati a rivelarla. Egli diceva sempre designing and building instrumentation of che una buona fisica si deve fare e teoricamente unprecedented quality, and providing support e sperimentalmente senza mai eccedere nel for establishing in Palermo a complete line of formalismo matematico. cryogenic facilities. Results included: Questo insegnamento, da lui rigorosamente 1) Highlighting the key relation between phonon applicato alla fisica della Gravità, ha formato molti and optical spectra in paramagnetic crystals. ricercatori che ora sono impegnati nella ricerca. 2) Sorting out the cascade of photostimulated Per questo dobbiamo essergli riconoscenti per la electronic and ionic processes in Silver Halide sua opera scientifica e didattica a favore della fisica crystals, and the way to govern it. italiana. 3) Evidencing a novel type of phase transition, concerning the dynamics of a subsystem of protons Pierluigi Fortini within the frame of much heavier atoms. Università di Ferrara Then, her interests shifted towards macromolecule and protein physics. These studies (combining molecular dynamics simulations, static and dynamic light scattering, and CD experiments) have greatly contributed to the time and space multiscale view of the interplay among All’età di 84 anni è venuto a mancare il Professor Beatrice Palma-Vittorelli Venzo De Sabbata. protein conformation, dynamics, aggregation, Ha svolto la sua attività di ricerca assieme crystallization, and the solvent’s statistical all’insegnamento di Relatività Generale presso le mechanics. They have also shown that very often Università di Bologna e di Ferrara. nucleation processes of protein aggregates and La sua attività ha riguardato la fisica della crystals share unsuspected universality features, Gravitazione e la Relatività Generale ove ha stemming from the universal scaling properties apportato notevoli contributi sia nel campo teorico of critically divergent fluctuations. This allows che in quello sperimentale (ricerca delle onde in-depth understanding of the underlying gravitazionali). fundamental physics, and related predictive power De Sabbata ha svolto la parte teorica in and control of nucleation. Significantly, the last full collaborazione con illustri studiosi della materia. paper she has contributed and co-authored is just In particolare ricordo qui la collaborazione con in press, still to appear on Faraday Discussions, with l’allievo di Einstein, il Professor Nathan Rosen, the record of a long, interesting discussion by many con cui ha realizzato sviluppi tendenti a cercare participants. una generalizzazione della Relatività Generale The above list shows Beatrice’s extraordinary (teoria bimetrica della gravità). In questo contesto commitment and achievements in research, di collaborazioni internazionali va inserita teaching, organization and family life. This is l’organizzazione, con cadenza annuale, di corsi Maria Beatrice Palma-Vittorelli, Emeritus Professor all the more true if the point of departure and relativi alla teoria della gravità e alla sua parte of Physics at the University of Palermo and the environmental conditions of her whole sperimentale. I corsi avevano luogo presso il Emeritus Fellow of the Società Italiana di Fisica, enterprise are taken into account. But Beatrice was Centro Ettore Majorana di Erice, nel quadro passed peacefully away on August 1st, 2008. She extraordinary. In her drive to let things happen, della International School of Cosmology and was born in Roma (1930), did University studies in she reconciled her spirit of hard worker with that Gravitation “Peter G. Bergmann” di cui De Sabbata Palermo and post-doc work at MIT (Strandberg) of gran Signora; her razor-sharp logics with her divenne il direttore. In particolare va appunto and Harvard (van Vleck). sudden flashes of imagination; her bent towards ricordato un interessante corso della Scuola sulla Back in Palermo, she joined forces with her personal understanding and forgiving with her generalizzazione della Relatività Generale al campo colleague and husband M. U. Palma and devoted proverbial rigidity in ethical matters. We are complesso. decades of strenuous efforts to research and to missing her dearly. Con riferimento alla parte sperimentale, De basic and advanced teaching. This was aimed Sabbata va citato per il suo lavoro per rivelare le (under Bruno Rossi’s and Edoardo Amaldi’s Lorenzo Cordone onde gravitazionali. Infatti egli propugnò l’uso di encouragement) at spotting and educating University of Palermo un interferometro che doveva essere confrontato promising students, to be later trained elsewhere in con l’uso di una antenna gravitazionale di tipo diverse fields and attracted back in Palermo, to help Weber. diversifying research activities there. New research Egli ne era così persuaso da convincere della fields so promoted, adding to established work sua idea il CNR per finanziargli uno studio sulla on condensed matter and magnetic resonances possibilità di usare un tale interferometro, in un include biophysics, quantum electrodynamics, momento in cui il parlare di onde gravitazionali era statistical simulations of molecular dynamics, considerato quasi fantascientifico. physics teaching, optoelectronics and (with Bruno Non va taciuto il grande impegno didattico che il Rossi’s fundamental help), astrophysics and the Professor De Sabbata profuse nell’educare i giovani revival of the historical astronomical observatory. al concetto fondamentale che la Relatività Generale All that generated the conditions for establishing era innanzi tutto una scienza sperimentale. I suoi in Palermo two new institutes by the physical corsi partivano sempre da quanto era già stato sciences branch of CNR. In addition to science, she appurato sperimentalmente per giungere alla took a relentless loving care of her two children proposta di ulteriori prove sperimentali. and of her family, and opened cheerfully her Così in generale tutti i suoi lavori sono improntati home to visitors, colleagues, students and a wide, ad un formalismo molto raffinato, quale appunto sometimes memorable, spectrum of friends. è la matematica della teoria einsteiniana, però Her group and herself had solved some “standing

vol24 / no5-6 / anno2008 > 107 opinioni

La sicurezza del collider LHC del CERN Anche il Premio Nobel delude?

è partita anche in Italia, proprio alla vigilia del tanto Ancora una volta la fisica italiana è stata dimenticata atteso avvio del progetto LHC del CERN, una campagna nell’assegnazione dei premi Nobel. “Dimenticanza” che di stampa allarmistica sui presunti rischi di questo dura da troppi anni. Basti pensare, verso la metà del formidabile progetto la cui realizzazione si deve secolo scorso, al premio, mai assegnato ai fisici italiani all’impegno già da oltre un decennio di una vastissima Ettore Pancini, Oreste Piccioni e Marcello Conversi, per comunità scientifica internazionale, non soltanto il celebre esperimento che portò nel 1947 alla scoperta, europea. nei raggi cosmici, della particella in seguito nota come Il 10 settembre 2008, due fasci di protoni di muone. elevatissima energia collideranno uno contro l’altro Altra duplice occasione mancata è quella di Giuseppe per la prima volta nel Large Hadron Collider (LHC), una Occhialini: il premio Nobel fu assegnato ai soli inglesi gigantesca macchina acceleratrice circolare, lunga 27 Patrick M.S. Blackett nel 1948 e Cecil F. Powell nel km, situata a 100 m di profondità vicino Ginevra, presso 1950, rispettivamente per lo sviluppo della camera il Laboratorio Europeo di Fisica delle Particelle (CERN). di Wilson e le scoperte con essa effettuate nella Si tratta di un avvenimento scientifico staordinario, di radiazione cosmica, e per lo sviluppo della tecnica delle enorme portata. emulsioni fotografiche e la scoperta del mesoneπ . Si Ciò nonostante accade di leggere sulla stampa articoli dimenticarono in entrambi i casi del fondamentale allarmisitici che paventano la possibilità di eventi contributo di Occhialini, peraltro riconosciuto dallo di estrema pericolosità originati dalle collisioni, che stesso Blackett. addirittura metterebbero a repentaglio l’esistenza del Nel 1995 il premio Nobel fu assegnato per metà nostro pianeta. Si tratta in realtà di pura fantascenza a Frederick Reines per la scoperta del neutrino di nessun fondamento scientifico. Basti pensare che elettronico. L’altra metà andò a Martin L. Perl per la Terra è bombardata da miliardi di anni dai raggi la scoperta del leptone τ e non fu condivisa con il cosmici. Ogni anno miliardi di collisioni delle particelle fisico italiano Antonino Zichichi, colui che ebbe l’idea dei raggi cosmici con i nuclei della Terra avvengono originale di un leptone pesante con il suo neutrino. A a energie maggiori o uguali a quelle che avverranno quel tempo Nicola Cabibbo fece notare che “la ricerca in LHC. Ma la Terra, e gli altri pianeti, non hanno mai di un leptone più pesante della particella mu, conclusasi subito alcun danno. con la scoperta di Perl, era incominciata alla fine degli La SIF invita a visitare il sito web del CERN: http:// anni sessanta per opera del gruppo di Zichichi a Frascati” www.cern.ch e, in particolare, la pagina “The e nella prefazione del libro “Lepton Physics at CERN safety of the LHC”: http://public.web.cern. and Frascati” (1994) scrisse: “The idea of a charged Heavy ch/public/en/LHC/Safety-en.html, dove, Lepton, carrying a new lepton number and accompanied con parole semplici, destinate a un vasto pubblico, by its neutrino, had no theoretical motivation. vengono date risposte scientificamente rigorose e Nevertheless it was Nino’s idea and his first priority in his pienamente rassicuranti a tanti (leciti) quesiti. Il sito experimental work at CERN”. web del CERN è molto ricco di notizie, di video e audio Nel 1984, il premio Nobel dato a Carlo Rubbia e Simon interviste a numerosi esperti, nei quali questo tema Van der Meer (a completamento di quello dato nel della sicurezza è esaurientemente affrontato. Vale 1979 a Sheldon L. Glashow, Abdus Salam e Steven anche la pena soffermarsi sulle splendide immagini Weinberg), riportò all’attenzione di tutti la miscela del collider LHC e dei favolosi apparati sperimentali scoperta circa venti anni prima da Cabibbo tra stati di costruiti per compiere questo ulteriore grande passo quark della prima e della seconda famiglia. Fu Zichichi avanti nella ricerca in fisica fondamentale, da sempre a scrivere in quell’occasione:“Sta qui la genialità intuitiva fonte di progresso e prosperità. di Nicola Cabibbo. Nonostante le pochissime cose note in quegli anni, egli seppe affermare una grande verità: Dunque, tutti tranquilli. Sta per partire uno dei progetti le forze deboli “vedono” le particelle fondamentali delle scientifici più affascinanti mai concepiti dall’umanità. varie famiglie in modo nettamente diverso da come fanno Dobbiamo esserne molto fieri, dar prova di entusiasmo le altre forze fondamentali della Natura. E per primo ne e curiosità, non certo di paura e creduloneria. misurò la diversità”. L’angolo di Cabibbo, nato nel 1963, era lo strumento nuovo. Alessandro Bettini Nonostante questo angolo abbia avuto un ruolo Università di Padova estremamente importante nello sviluppo della teoria Luisa Cifarelli delle interazioni deboli, il Comitato Nobel ha preferito Università di Bologna ignorarlo a vantaggio della “origine della rottura della simmetria che prevede almeno tre famiglie di quark in Pubblicato Online First il 2 settembre 2008 Natura”.

Ida Ortalli Università di Parma

Pubblicato Online First il 7 ottobre 2008

108 < il nuovo saggiatore recensioni

M. Cini - Elementi di Fisica Teorica. G. Benenti, G. Casati and G. Strini Springer-Verlag Italia, Milano. 2006; Principle of Quantum Computation pp. 260; € 28,95 and Information. Vol. II: Basic Tools and Special Topics. World Scientific, Scrivendo in un numero precedente (24, no. 1-2, 94 (2008)) del Topics and Methods Singapore 2007; pp. 350; € 35.57 in Condensed Matter Physics di Michele Cini, sarebbe stato naturale rifarsi al testo che Ho avuto già occasione di parlare da queste quantistica, i vari aspetti e modelli della l’autore aveva precedentemente realizzato colonne (Il Nuovo Saggiatore Vol. 21; no. decoerenza, la correzione degli errori per gli studenti del triennio di scienza dei 1-2; pp. 97-98, (2005)) del primo volume di quantistici e i primi esempi di implementazione materiali. Provvedo in ritardo. Questo testo, questo testo dedicato ai fondamenti della sperimentale di computazione quantistica. come il Topics and Methods, nasce direttamente computazione e informazione quantistica. Quest’ultimo capitolo è di grande interesse sul campo dell’insegnamento. Rivolgendosi L’insieme dei due volumi costuisce un’opera per i fisici di materia condensata, sia nel campo però a una fascia di studenti più giovani imponente, la prima ad affrontare da un dell’elettronica quantistica che in quello e quindi meno preparati, l’autore si pone punto di vista veramente didattico un tema delle nanotecnologie. Gli autori presentano l’obiettivo di motivare e stimolare il loro di enorme quanto recente interesse e sempre anche, come special topics asteriscate, alcuni interesse per la fisica teorica, di non spaventarli in rapida evoluzione. Da questo punto di vista argomenti di grandissimo interesse generale, ai con troppa matematica, ma piuttosto di l’impresa è coraggiosa, dal momento che quali hanno peraltro dato contributi personali insegnar loro il “come si fa”, ossia condurli occorre individuare nella grande massa di di ricerca assai rilevanti. Essi riguardano per mano alla soluzione di molti interessanti lavori recenti sull’argomento i concetti generali l’evoluzione del concetto fisico di entropia, problemi. Il testo offre un’ampia rassegna e un filo conduttore consolidato, destinati a il caos quantistico e la sua relazione con la della fisica teorica elementare che serve ai durare. computazione quantistica, la crittografia materialisti, dai complementi di fisica classica Il problema si pone soprattutto nel secondo quantistica, la comunicazione quantistica con ai fondamenti della meccanica quantistica. volume, dedicato ai vari aspetti teorici e fotoni e il teletrasporto. Oltre ai capitoli essenziali per i materialisti può sperimentali della computazione e informatica Vorrei aggiungere un piccolo elogio agli autori far specie trovare gli elementi di teoria della quantistica che aprono prospettive di per avere pensato non solo agli studenti e relatività, stimando che per loro essa non sia applicazione in un prossimo futuro. La giovani ricercatori del settore, ma, senza dirlo di grande utilità. Ma, grazie all’efficacia dello numerazione dei capitoli e la numerazione esplicitamente e con molto tatto, anche a stile didattico, alla fine del corso gli studenti delle pagine procede dal primo volume, noi professori di altri settori, che vorremmo saranno molto lieti di avere appreso argomenti a indicare una perfetta continuità, anche disperatamente tenerci aggiornati, cercando comunque di grande interesse generale e didattica. è specificato che il volume è di capire i formidabili articoli, molto tecnici e anche molto formativi. In fondo i materialisti pensato per un corso complementare di stringati, che compaiono su “Physical Rewiew dichiarano, a seconda delle circostanze e senza laurea triennale e per un corso ad hoc di Letters”, “Nature” e “Science”. Per non parlare offesa per nessuno, di essere “fisici che sanno la laurea specialistica (e posso testimoniare che delle mirabolanti versioni giornalistiche, che chimica” o “chimici che sanno la fisica” o ancora funziona), mentre il secondo volume è adatto già ci teletrasportano da un capo all’altro “ingegneri quantistici”. Comunque la si prenda, a un corso di indirizzo della specialistica e del pianeta come le macchine di Archimede ognuna di queste vanterie implica un buon a studenti di dottorato che si dedicano a Pitagorico. Questi due volumi, che raccomando corso di fisica teorica di base, e Michele Cini ha questo campo di ricerca, sia di fisica, che di a tutti i colleghi nelle suddette condizioni, ci egregiamente contribuito all’aspirazione dei matematica, che di informatica, purchè con riportano sul solido terreno della nostra buona materialisti di essere prima di tutto buoni fisici. una buona base di meccanica quantistica. meccanica quantistica. I quattro capitoli del secondo volume coprono Giorgio Benedek in modo esauriente la teoria dell’informazione Giorgio Benedek

vol24 / no5-6 / anno2008 > 109 scelti per voi

Energia solare per fabbricare Metamateriali e superlenti Occhi elettronici idrocarburi I recenti sviluppi di metodi di micro e Tutti gli esseri viventi hanno occhi di forma L’anidride carbonica ha una pessima nanofabbricazione stanno dimostrando la approssimabile a quella sferica, mentre i reputazione ormai da anni, per i noti problemi possibilità di controllare la propagazione sistemi artificiali sono basati su sensori che climatici. Per questo motivo appaiono della luce in modi che non sono possibili con formano immagini su superfici piane: queste particolarmente interessanti alcune idee i materiali presenti in natura. I metamateriali sono tappezzate con fotorivelatori che che si propongono di usare energia solare stanno aprendo la strada verso applicazioni possono produrre immagini con più di dieci per ridurre l’anidride carbonica a ossido di finora considerate impossibili: in analogia milioni di informazioni. La scelta dei sistemi carbonio che, con aggiunta di idrogeno e alla relatività generale in cui spazio e tempo naturali è di gran lunga migliore perché l’ottica opportuni catalizzatori, può essere trasformato sono curvati, la nuova ottica mostra che geometrica fuziona assai meglio con superfici in idrocarburi liquidi. Un processo del genere, anche lo spazio percorso dalla luce può curve che non con superfici piane. Nel caso di noto come processo Fischer-Tropsch fu essere reso curvo in modo del tutto arbitrario, superfici piane, per correggere le distorsioni inventato nel 1920 e utilizzato durante la lungo percorsi progettati con precisione tipiche dei bordi delle lenti, occorre aumentare seconda guerra mondiale dalla Germania, nanometrica. il loro numero facendo crescere il peso e il per ottenere petrolio partendo dal carbone Come ben noto, la luce si propaga in modo costo dell’apparato e diminuendo la luminosità gassificato, e dal Sud Africa quando le sanzioni che il cammino ottico, dato dall’integrale delle immagini. L’occhio artificiale elettronico applicate contro la discriminazione razziale di linea dell’indice di rifrazione n, risulti un sviluppato da un gruppo dell’ Università provocarono il blocco delle importazioni di estremo, in pratica un minimo relativo. Di dell’Illinois è stato progettato in modo da petrolio. conseguenza, creando opportune distribuzioni essere deformabile e comprimibile così da LARE, una società che opera nel New Mexico, spaziali della costante dielettrica e della poter essere modellato ed assumere una forma ha costruito un prototipo di reattore su piccola permeabilità magnetica è possibile controllare emisferica.

scala in cui CO2 viene iniettata in una camera il percorso della luce su tutte le scale spaziali, La fase iniziale del processo di fabbricazione di reazione con un concentratore solare che dalle dimensioni macroscopiche fino a consiste nel produrre, su un supporto di silicio, permette di raggiungere la temperatura di dimensioni inferiori a quelle della lunghezza un insieme di rivelatori fotoconduttori tali

2400 °C sufficenti a produrre la scissione di CO2 d’onda: si può, ad esempio impedire alla da sopportare una compressibilità elastica, in CO + O. Nell’arco di un anno LARE metterà luce di penetrare in particolari regioni di malgrado l’elevato livello delle tensioni a punto un nuovo prototipo di reattore di spazio, rendendo così invisibile ciò che è necessarie: il merito di questa tolleranza spetta maggiore potenza che permetterà di valutare contenuto in esse. Più interessante appare tutto ai sottili fili metallici che interconnettono la quantità di CO producibile. Un gruppo rivale, quello che può sembrare una specie di i fotorivelatori. La seconda innovazione che opera a Sandia (laboratorio nazionale del dispositivo complementare che permette di consiste nella scelta di un materiale che DOE statunitense), sta sviluppando un sistema concentrare la luce in una particolare regione permetta la trasformazione in forma emisferica denominato CR5 che funziona a temperature dello spazio, indipendentemente dalla di una configurazione piana. Poiché durante meno estreme, consistente in un disco direzione da cui proviene. Le trasformazioni la trasformazione dalla geometria planare a ruotante costituito da un materiale ceramico ottiche di cui stiamo trattando permettono quella emisferica intervengono significative che, riscaldato a 1500 °C libera ossigeno anche la costruzione di lenti piane che deformazioni meccaniche, gli autori hanno che recupera a 1100 °C, quando circola in trasformano i campi dell’onda evanescente sviluppato modelli basati sulla tecnica di

atmosfera di CO2. (che portano informazioni sulla struttura analisi agli elementi finiti per determinare Centi, della Università di Messina, ha ideato una dell’oggetto su dimensioni inferiori a quelle le distribuzioni spaziali dei fotorivelatori, cella che produce nonano e etilene, che sono della lunghezza d’onda, e la cui ampiezza come pure quelle (che avvengono durante blocchi importanti per ottenere le plastiche diminuisce all’aumentare della distanza con il processo) degli sforzi e degli spostamenti e altri materiali comunemente derivati dal legge esponenziale) in normali onde luminose. fra le interconnessioni dei rivelatori. Questa petrolio. La cella di Centi è un lontano parente Simulazioni effettuate sulle superlenti tecnologia annuncia l’avvento di una nuova della cella a combustibile che genera elettricità hanno dimostrato che potrebbero diventare classe di strumenti a grande angolo, bassa facendo reagire idrogeno o metanolo con normali accessori per i comuni microscopi, distorsione e dimensioni compatte. ossigeno, funzionando però a rovescio. Da di cui aumenterebbero il potere risolutivo, un lato della cella si trova un catalizzatore di permettendo di osservare l’onda evanescente Nature, 454, 7 agosto 2008, pp. 703 e 748 diossido di titanio che permette la rottura delle che porta informazioni sui dettagli a distanze molecole di acqua, quando sono investite inferiori a quelle della lunghezza d’onda. dai fotoni della luce solare, in ioni idrogeno e Con una superlente, al posto di una comune ossigeno gassoso: gli ioni idrogeno migrano lente di ingrandimento, potremo un giorno attraverso una membrana permeabile ai osservare oggetti di piccole dimnsioni, quali protoni oltre la quale un catalizzatore costituito cellule, virus e frammenti di DNA? da nanotubi di platino facilita le reazioni con

CO2, che producono idrocarburi. L’ energia che Science, 322, 17 ottobre 2008, p. 384 sarebbe liberata usando tali idrocarburi come combustibili rappresenta circa 1% dell’energia solare necessaria a produrli, non male perchè superiore a quella della fotosintesi delle piante. a cura di Sergio Focardi

New Scientist, 1 marzo 2008, p. 32

110 < il nuovo saggiatore indici del volume 24

INDICE PER FASCICOLI Borexino: un rivelatore unico per lo studio dell’oscillazione dei neutrini di bassissima energia Numero 1/2, 2008 G. Bellini, L. Miramonti, G. Ranucci 46 Scienza e tecnologia di un combustibile compatibile con Editoriale/Editorial l’ambiente: l’idrogeno L. Cifarelli 3 A. Miotello 59 Cutting the cost of electricity in D-He3 Tokamak reactors Domenico Pacini, un pioniere dimenticato dello studio dei A. Sestero 5 raggi cosmici Misure con attivazione neutronica sulla presenza di arsenico A. De Angelis, N. Giglietto, L. Guerriero, E. Menichetti, nei capelli di Napoleone Bonaparte e di suoi famigliari P. Spinelli, S. Stramaglia 70 M. Clemenza, E. Fiorini, L. Guerra, C. Herborg, M. Labra, Lev Landau: A physics genius on a logarithmic scale E. Orvini, A. Piazzoli, E. Previtali, F. Puggioni, A. Santagostino 19 S. M. Kiselev 75 Le cellule staminali incontrano le grandi macchine della fisica XCIV Congresso Nazionale della Società Italian di Fisica F. Rustichelli 31 Programma Generale 79 Il filo di Ariane: la nascita dell’Europa spaziale Energia: una sfida per la fisica del XXI secolo A. Russo 36 E. De Sanctis 82 L’onda evanescente e la nano-ottica EPS: i primi 40 anni M. Allegrini 46 A. Di Virgilio 89 Programma della Scuola estiva “Enrico Fermi”, Varenna 55 In ricordo di Beppe Nardulli (1948-2008) XCIV Congresso Nazionale 59 P. Colangelo, N. Cufaro 92 Bandi dei concorsi a premi della SIF 63 In ricordo di Domenico Brini (1923-2008) L’istituto Galileo Galilei per la Fisica Teorica F. Casali, G. Di Cocco, S. Focardi, G. Giacomelli, G. Maltoni, R. Casalbuoni 67 M. P. Morigi 92 Indagine sui laureati in Fisica a Bologna nel periodo 1991-2005 Recensioni 93

M. Spurio 74 Il mesone Bs - Orologi campione - Lenti gravitazionali e La Società Europea di Fisica alla frontiera delle sfide del XXI materia oscura secolo S. Focardi 99 R. A. Ricci 88 Annunci 100 In ricordo di Carlo Caso M. Giannini 89 Numero 5/6, 2008 In ricordo di Pier Giorgio Merli G. Lulli 89 In ricordo di / In memory of Giuseppe Franco Bassani Cerimonia a Torino in onore di Carlo Castagnoli G. La Rocca, G. Grosso 3 L. Ferrero 90 Editoriale/Editorial Opinioni 92 L. Cifarelli 5 Recensioni 94 Photons, dust, and honeybees Morire di inquinamento acustico - Il Geckil, un nuovo tipo di D. Wiersma 7 colla - A quanto ammontano le riserve mondiali di carbone? Electronic and transport properties of pristine graphene S. Focardi 96 nanoribbons Annunci 97 A. Cresti 16 Optical tweezers and their applications Numero 3/4, 2008 E. Di Fabrizio 27 Max Planck - A conservative revolutionary Editoriale/Editorial M. Cardona, W. Marx 39 L. Cifarelli 3 Fresnel, the prince of the opticians La missione Cassini-Huygens: 4 anni in orbita attorno a Saturno R. Colella 55 F. Capaccioni 5 Cerimonia Inaugurale XCIV Congresso Nazionale della Alla ricerca degli aggregati nucleari kaonici Società Italiana di Fisica 62 T. Bressani, A. Panzarasa 17 The 40th anniversary of EPS: Gilberto Bernardini’s Trasporto in nanofili di semiconduttore contributions to the Physics of the XX century S. Roddaro 28 A. Zichichi 77 Il caos quantistico Premio Nobel per la fisica 2008 G. Casati 36 A. Bettini 98

vol24 / no5-6 / anno2008 > 111 ESOF 2010 Colella R., Fresnel, the prince of the opticians 24:5/6, 55 E. Predazzi, A. De Bortoli 103 Cordone L., In ricordo di Beatrice Palma-Vittorelli 24:5/6, 107 Premio Sergio Fubini 2008 Cresti A., Electronic and transport properties of G. Marchesini 105 pristine graphene nanoribbons 24:5/6, 16 Progetto Lauree scientifiche: borse SIF Cufaro N. (vedi Colangelo P.) V. Grasso 105 In ricordo di Frederick Seitz D G. F. Bassani, G. Chiarotti 106 De Angelis A., Giglietto N., Guerriero L., Menichetti E., In ricordo di Venzo De Sabbata Spinelli P., Stramaglia S., Domenico Pacini, un pioniere P. Fortini 107 dimenticato dello studio dei raggi cosmici 24:3/4, 70 In ricordo di Beatrice Palma-Vittorelli De bortoli a. (vedi Predazzi E.) L. Cordone 107 De Sanctis E., Energia: una sfida per la fisica del Opinioni 108 XXI secolo 24:3/4, 82 Recensioni 109 Di Virgilio A., EPS: i primi 40 anni 24:3/4, 89 Energia solare per fabbricare idrocarburi - Metamateriali Di Cocco G. (vedi Casali F.) e superlenti - Occhi elettronici Di Fabrizio E., Optical tweezers and their applications 24 :5/6, 27 S. Focardi 110 F Ferrero L., Cerimonia a Torino in onore di Carlo INDICE PER AUTORI Castagnoli 24:1/2, 90 Fiorini E. (vedi Clemenza M.) A Focardi S. (vedi Casali F.) Allegrini M., L’onda evanescente e la nano-ottica 24:1/2, 46 Fortini P., In ricordo di Venzo De Sabbata 24:5/6, 107

B G Bassani G. F., Chiarotti G., In ricordo di Giacomelli G. (vedi Casali F.) Frederick Seitz 24:5/6, 106 Giannini M., In ricordo di Carlo Caso 24:1/2, 89 G. Bellini, L. Miramonti, G. Ranucci, Borexino: un Giglietto N. (vedi De Angelis A.) rivelatore unico per lo studio dell’oscillazione dei Grasso V., Progetto Lauree scientifiche: borse SIF 24:5/6, 105 neutrini di bassissima energia 24:3/4, 46 Grosso G. (vedi La Rocca G.) Bettini A., Premio Nobel per la fisica 2008 24:5/6, 98 Guerra L. (vedi Clemenza M.) Bressani T., Panzarasa A., Alla ricerca degli Guerriero L. (vedi De Angelis A.) aggregati nucleari kaonici 24:3/4, 17 H C Herborg C. (vedi Clemenza M.) Capaccioni F., La missione Cassini-Huygens: 4 anni in orbita attorno a Saturno 24:3/4, 5 K Cardona M., Marx W., Max Planck - A conservative Kiselev S. M., Lev Landau: A physics genius on a revolutionary 24:5/6, 39 logarithmic scale 24:3/4, 75 Casalbuoni R., L’istituto Galileo Galilei per la Fisica Teorica 24:1/2, 67 L Casali F., Di Cocco G., Focardi S., Giacomelli G., Labra M. (vedi Clemenza M.) Maltoni G., Morigi M. P., In ricordo La Rocca G., Grosso G., In ricordo / In memory of di Domenico Brini (1923-2008) 24:3/4, 92 Giuseppe Franco Bassani 24:5/6,3 Casati G., Il caos quantistico 24:3/4, 36 Lulli G., In ricordo di Pier Giorgio Merli 24:1/2, 89 Chiarotti G. (vedi Bassani G. F.) Clemenza M., Fiorini E., Guerra L., Herborg C., M Labra M., Orvini E., Piazzoli A., Previtali E., Puggioni F., Maltoni G. (vedi Casali F.) Santagostino A., Misure con attivazione neutronica Marchesini G., Premio Sergio Fubini 2008 24:5/6, 105 sulla presenza di arsenico nei capelli di Napoleone Marx W. (vedi Cardona M.) Bonaparte e di suoi famigliari 24:1/2, 19 Menichetti E. (vedi De Angelis A.) Colangelo P., Cufaro N., In ricordo di Miotello A., Scienza e tecnologia di un combustibile Beppe Nardulli (1948-2008) 24:3/4, 92 compatibile con l’ambiente: l’idrogeno 24:3/4, 59

112 < il nuovo saggiatore Miramonti L. (vedi Bellini G.), graphene nanoribbons Morigi M. P. (vedi Casali F.) A. Cresti 24:5/6, 16 Il caos quantistico O G. Casati 24:3/4, 36 Orvini E. (vedi Clemenza M.) La missione Cassini-Huygens: 4 anni in orbita P attorno a Saturno Panzarasa A. (vedi Bressani T.) F. Capaccioni 24:3/4, 5 Piazzoli A. (vedi Clemenza M.) Photons, dust, and honeybees Predazzi E., De Bortoli A., ESOF 2010 24:5/6, 103 D. Wiersma 24:5/6, 7 Previtali E. (vedi Clemenza M.) Trasporto in nanofili di semiconduttore Puggioni F. (vedi Clemenza M.) S. Roddaro 24:3/4, 28

R FISICA E... Ranucci G. (vedi Bellini G.), Ricci R. A., La Società Europea di Fisica alla frontiera Le cellule staminali incontrano le grandi macchine delle sfide del XXI secolo 24:1/2, 88 della fisica Roddaro S., Trasporto in nanofili di semiconduttore 24:3/4, 28 F. Rustichelli 24:1/2, 31 Russo A., Il filo di Ariane: la nascita dell’Europa Misure con attivazione neutronica sulla presenza spaziale 24:1/2, 36 di arsenico nei capelli di Napoleone Bonaparte e Rustichelli F., Le cellule staminali incontrano le di suoi famigliari grandi macchine della fisica 24:1/2, 31 M. Clemenza, E. Fiorini, L. Guerra, C. Herborg, M. Labra, E. Orvini, A. Piazzoli, E. Previtali, S F. Puggioni, A. Santagostino 24:1/2, 19 Santagostino A. (vedi Clemenza M.) Optical tweezers and their applications Sestero A., Cutting the cost of electricity in D-He3 E. Di Fabrizio 24:5/6, 27 Tokamak reactors 24:1/2, 5 Scienza e tecnologia di un combustibile Spinelli P. (vedi De Angelis A.) compatibile con l’ambiente: l’idrogeno Spurio M., Indagine sui laureati in Fisica a Bologna A. Miotello 24:3/4, 59 nel periodo 1991-2005 24:1/2, 74 Stramaglia S. (vedi De Angelis A.) PERCORSI

W Domenico Pacini, un pioniere dimenticato dello Wiersma D., Photons, dust, and honeybees 24:5/6, 7 studio dei raggi cosmici A. De Angelis, N. Giglietto, L. Guerriero, Z E. Menichetti, P. Spinelli, S. Stramaglia 24:3/4, 70 Zichichi A., The 40th anniversary of EPS: Gilberto Fresnel, the prince of the opticians Bernardini’s contributions to the Physics of the R. Colella 24:5/6, 55 XX century 24:5/6, 77 Il filo di Ariane: la nascita dell’Europa spaziale A. Russo 24:1/2, 36 L’onda evanescente e la nano-ottica INDICE PER RUBRICHE M. Allegrini 24:1/2, 46 Lev Landau: A physics genius on a logarithmic scale SCIENZA IN PRIMO PIANO S. M. Kiselev 24:3/4, 75 Max Planck - A conservative revolutionary Alla ricerca degli aggregati nucleari kaonici M. Cardona and W. Marx 24:5/6, 39 T. Bressani, A. Panzarasa 24:3/4, 17 Borexino: un rivelatore unico per lo studio IL NOSTRO MONDO dell’oscillazione dei neutrini di bassissima energia G. Bellini, L. Miramonti, G. Ranucci 24:3/4, 46 Congressi SIF e atti societari Cutting the cost of electricity in D-He3 Tokamak Programma della Scuola estiva “Enrico Fermi”, reactors Varenna 24:1/2, 55 A. Sestero 24:1/2, 5 XCIV Congresso Nazionale 24:1/2, 59 Electronic and transport properties of pristine Bandi dei concorsi a premi della SIF 24:1/2, 63

vol24 / no5-6 / anno2008 > 113 XCIV Congresso Nazionale della Società Italiana RECENSIONI di Fisica, Programma Generale 24:3/4, 79 Cerimonia Inaugurale XCIV Congresso Nazionale Atoms and Plasmas in Super-Intense Laser Fields, della Società Italiana di Fisica 24:5/6, 62 D. Batani, C. J. Joachain and S. Martellucci (Editors), The 40th anniversary of EPS: Gilberto Bernardini’s recensito da G. Benedek 24:1/2, 94 contributions to the Physics of the XX century E. Majorana – appunti inediti di fisica teorica, A. Zichichi 24:5/6, 77 S. Esposito, E. Recami (a cura di), recensito da G. Pisent 24:3/4, 93 Notizie generali Elementi Di Fisica Teorica, M. Cini, recensito da L’istituto Galileo Galilei per la Fisica Teorica G. Benedek 24:5/6, 109 R. Casalbuoni 24:1/2, 67 Ettore Majorana, Aspects Of His Scientific And Indagine sui laureati in Fisica a Bologna nel Academic Activity, F. Guerra and N. Robotti, periodo 1991-2005 recensito da M. Giannini 24:3/4, 98 M. Spurio 24:1/2, 74 Ettore Majorana Scientific Papers on the occasion La Società Europea di Fisica alla frontiera delle sfide of the centenary of the birth, G. F. Bassani and the del XXI secolo Council of The Italian Physical Society (Editors), R. A. Ricci 24:1/2, 88 recensito da G. Benedek 24:3/4, 96 Progetto Lauree scientifiche: borse SIF Flashes of Physics in Italy. A collection of scientific V. Grasso 24:5/6, 105 papers in memory of Carlo Castagnoli, R. A. Ricci (Editor), recensito da G. G. C. Palumbo 24:3/4, 95 Commemorazioni, profili e premi Fundamental Astronomy - forth edition, H. Karttunen, In ricordo di Carlo Caso P. Kroger, H. Oja, M. Poutanen, K. J. Donner (Editors), M. Giannini 24:1/2, 89 recensito da B. Bertotti 24:3/4, 93 In ricordo di Pier Giorgio Merli Introduction To Elementary Particle Physics, A. Bettini, G. Lulli 24:1/2, 89 recensito da L. Cifarelli 24:3/4, 98 Cerimonia a Torino in onore di Carlo Castagnoli Introduction to Mathematical Physics, M. T. Vaughn, L. Ferrero 24:1/2, 90 recensito da G. Capon 24:1/2, 95 In ricordo di Beppe Nardulli (1948-2008) Principle of Quantum Computation and Information. P. Colangelo, N. Cufaro 24:3/4, 92 Vol. II, G. Benenti, G. Casati, G. Strini, recensito da In ricordo di Domenico Brini (1923-2008) F. Casali, G. Benedek 24:5/6, 109 G. Di Cocco, S. Focardi, G. Giacomelli, G. Maltoni, Rudimenti di meccanica quantistica, C. Rossetti, M. P. Morigi 24:3/4, 92 recensito da L. Sertorio 24:3/4, 96 Premio Nobel per la fisica 2008 The Scientific Legacy Of Bruno Rossi. A Scientific A. Bettini 24:5/6, 98 Colloquium In Honour Of Bruno Rossi on the Premio Sergio Fubini 2008 100th Anniversary of his Birth, Padova – Venezia, G. Marchesini 24:5/6, 105 September 16 – 17, 2005, A. Pascolini (Editor), In ricordo di Frederick Seitz recensito da G. G. C. Palumbo 24:3/4, 94 G. F. Bassani, G. Chiarotti 24:5/6, 106 Topics and Methods in Condensed Matter Theory. In ricordo di Venzo De Sabbata From Basic Quantum Mechanics to the Frontiers of P. Fortini 24:5/6, 107 Research, M. Cini, In ricordo di Beatrice Palma-Vittorelli recensito da G. Benedek 24:1/2, 94 L. Cordone 24:5/6, 107 SCELTI PER VOI Convegni, conferenze, seminari e mostre Energia: una sfida per la fisica del XXI secolo Morire di inquinamento acustico - Il Geckil, un nuovo E. De Sanctis 24:3/4, 82 tipo di colla - A quanto ammontano le riserve EPS: i primi 40 anni mondiali di carbone? 24:1/2, 96

A. Di Virgilio 24:3/4, 89 Il mesone Bs - Orologi campione - Lenti gravitazionali ESOF 2010 e materia oscura 24:3/4, 99 E. Pedrazzi, A. De Bortoli 24:5/6, 103 Energia solare per fabbricare idrocarburi - Metamateriali e superlenti - Occhi elettronici 24:5/6, 110

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