CNEA NT-14/88
Progress Report 1986/1987
Basic Research Department
Comisión Nacional de Energía Atómica
Dirección de Investigación y Desarrollo
Gerencia Centro Atómico Bariloche
8400 - Bariloche (R.N.) Argentina 1988 CNEA NT-14/88
Progress Report 1986/1987
Basic Research Department
Comisión Nacional de Energía Atómica
Dirección de Investigación y Desarrollo
Gerencia Centro Atómico Bariloche
8400 - Bariloche (R.N.) Argentina 1988 INDEX
Page
1. Introduction i
2. Table v
3. Atomic Collisions 1
4. Low Temperature Physics 23
5. Magnetic Resonance 49
6. Metal Physics 61
7. Neutron and Reactor Physics 79
H. Theoretical Physics - Computational Physics 91
9. Theoretical Physics - Elementary Particles 103
10. Theoretical Physics - Nuclear Physics 113
11. Theoretical Physics - Solid State 125
12. Appendix I - Department Staff 149
13. Appendix II - Visiting Scientists 151
14. Glossary 159 - i -
INTRODUCTION
This 1986-1987 Progress Report gives an overview of the organization, activities and future projections of the Basic Physics Department. A synthetic description is given In the Table following this Introduction.
Because each Division within the Department has its own specific characteristics, needs, and history, we have felt that a clearer picture would «merge by having each of them give their own Independent summary of lines of research, current work, and achievements within this period, with a brief description of facilities. There is however, a shared context which applies to the department as a whole and which is essential for a fuller vision.
Many years of sustained effort were necessary In order to achieve the present material Infrastructure of this Department, and its continuous growth was only possible through carefully planned investment.
The demanding present technical standards of the different shop facilities and the expertise of their st.aff, wnlch in another environment might be taken for granted, had to be built from the ground up. It is only fitting that this should be acknowledged In this Introduction.
Viewing the future, we feel that we are still short of our goals:
Even within our policy of thoughtful use of meagre budgets there are many areas in which considerable investment is still due for organic growth of the Department as a whole. Specific examples of this are optics and sample preparation and analysis. For the incorporation of these as well as of other areas, our main guidelines are harmonious growth and i :»l.oj;'i'a¡. i oil wilh ill"? a\\-".:MÍy •.-- i si. ing, facilities
:¡ ;.-.- ¡ry;;: i.-:-:,'.; !íepor¡ ..>!j.;! ¡i Le ; ¡'<:o::;p! •'•L»'¡ without, special mention of tli'.. ,HJW field of high T ai.;jercj¡'id>.¡ctlng material;;. This project began in
'••.i! ¡y l'.,H/ íjii'l involved the combined effoi Ls of all the Divisions of this
IK ¡.u.i-t r.iüiil.. Hose-arch on high T ceramic superconductors has been i ;:wui •!: rig l:i ¡•¡••v\y -úaparAs: A broader Find richer viewpoint on the physics
:•'. S in •.. •"• a\.\v cr i <-i! s, a new and st i mis I a l i na close col labrirat ion with the
,"fi|iiir:.! li^i;;;-u-fu ficpai l.raer.L and with scientists in other groups here and
;-jii--"-id, iind ;\ nuinher i-.C original com. f i but Ions and published papers. A t •: 11 =.i i \.- - - ni' thus I ¡i-">i year's work, however, while positive in having met a
. lv I I ( i.}'/; Í:'.:C:CGSÍ'UJ i y. t;till bears witness to the shortcomings in our'
!••••; .;.u-c:i?i; (chifífly for the preparation and characterization of samples).
)'!,::re is a der-o commitment to developing and maintaining closr^ lies with !.:ie academic coi.i.nurilty here and abroad. Basic among these is the
:.\ Ü¡'/''':. íc¡-, Lcpai-VHient, while not teaching forma) courses, supervise
:!."'. .'.; Jiivl Ph.D. theses. This strong academic Insertion is also borne
:-.-.;!• \>y ;"i)..: MTÍOUS meet i ngr;, \.vir-k'-;niipt: onti courses on Superconductivity, i \. oiiii.- í oJ i is ions aiid Solid State Fhyiiics within this period. Financial jiippo: I from Ji'TI' (Tri ei ! e i made it possible for nine Latin American
Se i or:., i:, i t; to Join the Department as research associates. Other cooperation agreements with several foreign institutions are li<;ted in detail sepHirat' ¡y. A lots! of forty-nine Argentine and eighty-six foreign
••;< i'intis.ts visited the O"partmi?nt during this period. More detalle»' ii.tiii million it; p,lven in trv Appendixes. - ill -
Our activities have been possible through the collaboration of many
men and women in Centro Atómico Bariloche who devote their time and effort
to supporting activities. I wish to thank all of them.
This report was edited through the joint effort of Veronica Grünfeld,
Alejandra Cohen, Norma Badino, Madeleine Ferreira and
Maria Elena de la Cruz.
Bias Alascio
Head Basic Research Department
San Carlos de Barí loche, June, 1988. STAFF DIVISION GRADUATE LINES OF RESEARCH SCIENTISTS TECHNICIANS PUBLICATIONS STUDENTS
Amorphous superconducting restáis, metallic multilayers, low LOW TEMPERATURE 7 11 5 33 PHYSICS dimensional systems, intermediate valence, ceraciic super- conductors. Ion-gas ¿lid ion—solid collision processes, emission and . , j ATOMIC COLLISIONS 11 12 capture of electrons in such processes. Surface physi.cs, interaction of ions with solid surfaces. ?! | Martensir.ic tr--¡nsf orna. Eior., thermcdynamic . .-. fy.-staii o graphic METAL PÜYSICS 7 7 2 •;nd kinetic :-; '• u J i e n of thio t cansfci ;,;itior.. li.f.ernal i'ric- j tion if! A.Í a'loys, ¿as jerectJor: ir, metáis.
í?eu£vcr: cif fri • "ion in so3 id and liquid condsn!:.= (! natter, NEUTROS & REACTOR 5 4 12 PHYSICS determiT;2ti.->r, ¡- * i fue tures , Dabye-Wsiler facr.crs. Neutron phvíics and calculations. i Magnetic imparities, spin 2Íass'-s> antiferremagnatí», one " '" ~1 MAGNETIC 6 6 1 RESONANCE dinensicr..-jl mí«¡s, magnetism in superconducting cera.Ei::s.
Anomalies in fialc! theoyajs, phsn^aieaoiogy o? supersymrnetric ELEMENTARY 5 7 -- 10 PARTICLES theories; singular Lagrsn^ians and canonical systems with constraints. Intermediate valence systerr.s, superconducting networks, SOLID STATE 1? 7 — 44 PHYSICS surface?, superlattices, disordered systems- high critical temperature superconductors.
SUCLEAR 3 2 — Theory of irreversible processes in nuclear dynamics, 11 PHYSICS Fokker-Planck equation, nuclear fission.
Spin glasses, optimization problems, neural systems,
THEORETICA L PHYSIC S COMPUTATIONAL 1 3 __ cellular automata, computational technology in parallel 7 PHYSICS architecture computers.
TOTAL 57 59 12 196 -z
ATOMIC COLLISIONS
1. STAFF
Scientists
M. Abbate + V. H. Ponce N. Arista E. Sánchez ++ H. Ascolani ++ S. Suárez ++ R. Barrachina G. Zampieri G. Bernard! ++ D. Zanette ++ N. Capuj ++ A. Ceballos L. de Ferrariis ++ Technicians J. C. Eckardt P. Fainstein + J. de Pellegrin P. Focke C. Wenger C. R. Garibotti ** J. Gervasoni M. Guraya + IB Graduate G. Lantschner Student M. L. Martiarena ++ W. Meckbach * J. Sobehart
* CNEA/CONICET Researcher ** CONICET Researcher + CNEA Fellow ++ CONICET Fellow - 3 -
2. GENERAL DESCRIPTION
Research in this laboratory involves several processes of
interaction of ions and electrons with matter (solids, surfaces, gases
and plasmas).
2.1. Facilities:
Atomic collision experiments are performed using several
electrostatic accelerators, which include a 300-KV (Kevatron), a
100-KV (Kevatrito), a 10-KV (TOF) accelerators and a 2-MV van de Graaf
accelerator. The laboratory also has surface analysis equipment which
uses Auger, XPS, LEED and SIMS techniques. Other standard equipment
includes high vacuum systems, sample evaporators, electrostatic
analyzers, particle detectors and data acquisition systems.
2.2. Cooperation Agreements:
The various lines of research carried out have enabled the group
to develop cooperation agreements with local and foreign laboratories.
In recent years Joint research programs with the following groups
have been particularly relevant:
- Oak Ridge National Laboratory and University of Tennessee, Atomic
Collisions Group: Studies of electron transfer to the continuum
processes (NSF - CONICET Cooperation Agreement).
- University of Georgia, Department of Physics: Electron emission
induced by atomic collisions (NSF - CONICET Cooperation Agreement). • iiiotitul l'ür Kernphysik, Unlversi tal. Frankfurt: Fleet roa emission
in meed by atomic: collision;; on gaseous and solid targets
(¡Ici'mai',- Ai-gpnl. i ne ('ooperat ion Agreement CNl-'A-KJ'K I.
- Uiii •f-isilé do iiordesaix, l.aboratoi re dos CoJlisioncs Atomiques:
:it urii >.•:: on atomic collisions (French - Argentine Cooperation
Aj;r< emerit ) .
Mi.i i/cT^j dad d<- Al i cunto. Depart amento de lisica Aplicada, Alicante,
I-V.puñu.
V.'itliin Ar'genLÍ na the laboratory works in cooperation with-
ln;.l. it.ut.o do Pi sica do Itosario (1F1R), CON I GET, Rosario.
hisUlii'o 'ji; A;il r-onomía y Física del Fspacio Í1AFE}, Buenos Aires.
Instituto para el desarrollo Tecnológico de la Industria Química
( IN'I !•.(,"), Siintü. F6.
- I.-Locutorio TANÜAR, CNtA, Buenos Aires.
Ü.'Í.'J. Organized by our Laboratory:
With the support, of CNKA and Secretaría de Ciencia y Técnica,
Argentina, the first. Latin American Workshop on Atomic Collisions was organized. It took place in our laboratory during 6-15 October, 1986. - 5 -
Participants: from Brazil (Universidade Federal do Rio de
Janeiro, Univ. Estadual de Sao Paulo, Pontificia Universidade
Católica), Colombia (Univ. Nacional de Colombia, Instituto de Asuntos
Nucleares), Chile (Universidad Católica), México (Univ. Nac.
Autónoma). - 6 -
3. RESEARCH PROGRAMS
A. Emission and capture of electrons in solids and gases:
a) "Kevatron" i ine
This research program covers processes of electron emission
induced by the interaction of atomic projectiles with gaseous and
solid targets. The emitted electrons originate from ionization of the
target or t.he projectile. Gaseous targets are produced by a molecular
beam of low velocity; solid foil targets are prepared by evaporation
in vacuum and subsequent dissolution of a plastic backing.
Double differential distributions -in angle and energy-of the
emitted electrons are measured. Of particular interest is the case in
which the electrons are emitted with velocities close in direction and
magnitudir to the velocity of the emerging projectiles. For these
elections the interact inn with the ionic projectile is strong.
Experimentally one observes a characteristic cusp shaped peak of so
called "convoy electrons" centered at this velocity.
During the present period we have performed the following
experiments:
- Using an electrostatic ion analyzer in tandem with our coaxial
electron spectrometer we localized the energy of the convoy electron
peak produced by beam-foil interaction with a precision of 0.2eV.
We are thus able to show that these electrons are not slowed down by
the surface potential. - 7 -
- We completed the construction and installation of a new
electrostatic electron analyzer which makes it possible to cover the
complete angular range of 360 deg and energies down to 2-3eV.
Extended Gas effects have been reduced to a minimum.
- With this equipment we measured double differential electron
distributions for protons and neutral hydrogen projectiles
interacting with Helium and for protons traversing a thin carbon foil.
These measurements complete existing information and permit a
quantitative comparison with theories.
- Measurements at higher energies were performed by W. Meckbach in
cooperation with investigators of the Frankfurt group, using the
UNILAC at GSI Darmstadt (KfK-CNEA agreement).
b) "Kevatrito" line
In this line we study electron emission for ion beams incident on solid surfaces at small angles, in reflection and transmission conditions, and with energies below lOOKeV.
Experiments performed:
- Electron emission in glancing collisions of protons with surfaces.
Measurements of double differential (angle-energy) distributions for
Si and Na:Si surfaces corresponding to protons reflected at the
surface.
- Similar studies for transmission of protons in Al foils and in Al
implanted with Na at the emergence surface. Influence of the work - a -
function on the electron emission characteristics.
- Study of Auger electron emission from Si surfaces using Ar ions at
various incidence and observation angles. Variation of the
distributions when Na ions are implanted on the Si target.
B. Experimental activities in surface physics: Ion-surface interactions:
This research line covers studies of electron emission from solids and electronic processes in surfaces using techniques of Auger
;;pec;troscopy (AES) and photoelectron spectroscopy using X-rays (XPS).
We have measured the rate of oxygen desorption from oxidized surfaces of Mg, M, and Si bombarded with 4KeV He, Ne, Ar, and Kr ion.1;. We have derived ion-induced oxygen desorption cross-sections which are in good agreement with theoretical estimations.
We have studied the Auger electron emission from surfaces bombarded with low-energy heavy ions. Auger decay processes inside and outside the solid have been clearly identified. Comparing the results of a Monte C^rlo simulation and the experiment we have determined important parameters.
We have made XPS analysis of several high-T superconductors and some Cu oxides.
We aro presently foJlowing in four research lines: Intrinsic and extrinsic electronic excitations in photoemisslon (Plasmas and e-h - 9 -
pairs), effect of surface conditions on ETC processes (Electron
Transfer to the Continuum of the Projectile), epitaxial growth of metallic films on different crystalline substrates, and XPS analysis of amorphous silicon-based semiconductors.
C. Interaction of. fast Ions with matter:
This research line includes experimental and theoretical studies of energy loss processes and multiple scattering of ions traversing thin solid foils.
The experiments are made using light ions with energies in the
50-300KeV range and with evaporated foils of thicknesses between 100 and lOOoX.
During this period the following studies have been made:
- Angular dependence of the energy corresponding to the maximum
stopping of protons in solids, and the shift in th • position of the
maximum for different angles of emergence of the beams. The study
was made on foils of aluminium, copper and silver.
A theoretical model was developed to explain the angular dependence
of the energy loss.
- Energy distributions of ion beams traversing thin solid foils. The
first three moments of the energy distributions were determined.
They give the values of the stopping power (first), straggling
(second) and skewness (third). Foils of A£, Cu, Ag and Zu were
used A theoretical model was used to represent the energy-loss
moments. - 10 -
- The relation between the energy-loss moments and the foil thickness
fluctuations was studied. Equations were obtained to determine the
foil roughness. This provides a new method for surface roughness
studies with a resolution of the order of loA.
D. Theoretical studies of atomic collision processes in gases, solids and plasmas:
The following aspects were covered:
- fnergy loss of ions in solids: A theoretical model was developed to
í^tudy electronic excitations and energy losses in atomic systems and
solids. It describes the energy loss fluctuations for all the atoms
in the periodic table.
- Energy loss of particles in plasmas: the model was extended to
describe atomic systems at high temperatures. The calculations
explain the observed enhancement of the energy loss of proton beams
in solids at very high temperatures.
- Laser field effects on the interaction of particles with plasmas.
The response function of dilute plasmas was calculated in the
presence of a laser field. The interaction of particles in the
plasma is strongly modified for laser intensities in the range of
interest of laser fusion research. - 11 -
4. CONFERENCES AND PUBLICATIONS
4.1. Conferences:
4.1.1. Internati onal Conferences:
15th INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS, Grado, Italy, 16 - 20 June, 1986:
"Iteration Scheme for the Solution of the Nonlinear Spatially Homogeneous Boltzmann Equation" D. H. Fuji!, R. 0. Barrachlna, C.R. Garibotti.
"Anisotropic Approach to Equilibrium in the Nonlinear Spatially Homogeneous Boltzmann Equation" R.O. Barrachina, C.R. Garibotti.
DEUTSCHE PHYSIKALISCHE GESELLSCHAFT, Federal Republic of Germany, 17 - 21 March, 1986:
"Konvoielectronen von Schnellen Leichten Ionen ais Antwort auf das Ladungsgleichgewicht im Festkorper" P. Koschar, 0. Hell, M. Burhard, J. Kemmler, W. Lotz, K.O. Groeneveld, A. Clouvas, J. Remlllieux, W. Meckbach.
lleme COLLOQUE DE LA PHYSIQUE SUR LES COLLISIONS ATOMIQUES ET ELECTRONIQUES, Metz, France, 1986:
"Ionization dans les Collisions Ion-Atome" P. D. Falnstein, R. D. Rivaróla.
9th CONFERENCE ON THE APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY, Dentón, Texas, U.S.A., 1986:
"Application of Distorted Wave Models for Electron Emission in Ion-Atom Collisions" R. D. Ri varóla, P. D. Fainstein.
ENCUENTRO LATINOAMERICANO DE COLISIONES ATÓMICAS, Bariloche, Argentina, 1986:
"Régimen Cuasiadlabático en Colisiones Atómicas" V.H. Ponce.
"Actividades Experimentales a Energías Intermedias en Bariloche" W. Meckbach.
"Interacción de Partículas con Sólidos y Plasmas Densos" N.R. Arista.
"Dependencia Angular del Frenamiento de Protones en Sólidos" M. M. Jakas, J.C. Eckartit, N. E. Capuj, G. Lantschner.
"Informe de Actividades Experimentales en Física de Superficies" M. Abbate. - 12 —
"Emisión Electrónica en Colisiones Rasantes de Iones con Superficies" L. de Ferrari is.
"Electrones en la Cresta Internúcleo y su Difracción en Láminas Sólidas" W. Meckbach.
"Estudio del Espectro de Electrones en la Colisión H - H. Descripción de la Cresta" M. L. Martiarena, V. H. Ponce.
"Dependencia Angular del Frenamiento de Protones en Láminas Sólidas" H. Ascolani, M. M. Jakas, N.R. Arista.
Xllth INTERNATIONAL CONFERENCE ON ATOMIC COLLISIONS IN SOLIDS" (ICACS), Okayama, Japan, 12 - 16 October, 1987:
"Double Differential Electron Distributions Induced by 170 keV H+-He, H°-He and H - Solid Foil Interactions" G.C. Bernard!, S. Suárez, P.R. Focke, W. Meckbach.
"Double Differential Spectra of Electrons Emitted from the Forward and Backward Surface of a Carbon Foil Traversed by a Beam of Hydorgenic Projectiles" S. Suárez, G.C. Bernardi, P.R. Focke, W. Meckbach.
"Calculated Convoy Electron Distributions Due to Electron Loss Collisions Inside Solid Targets" R.O. Barrachina, A. R. Goñl, P.R. Focke, W. Meckbach.
3rd WORKSHOP ON HIGH ENERGY ION ATOM COLLISIONS, Debregen, Hungary, 1987:
"Angular Distributions of Electrons Emitted in Proton-Helium Collisions" G.C. Bernard!, S. Suárez, P.R. Focke, W. Meckbach.
"Non-Equilibrium Convoy Electron Production in Coincidence with Outgoing Projectile Charge States" J. Kemmler, 0. Heil, C. Biedermann, P. Koschar, H. Rothard, K. Kroneberger, A. Kovér, G. Szabó, L. Gulyás, D. Berényi, P. Focke, W. Meckbach.
"Electron Emission at Small Angles in H -He Collisions" C.R. Garlbotti, D. H. Zanette, M.L. Martiarena.
10th WERNER BRANDT WORKSHOP ON PENETRATION PHENOMENA: DYNAMIC INTERACTIONS OF ENERGETIC PROBES WITH CONDENSED MATTER, Alicante, Spain, 1987:
"Energy Loss Slowness-Coefficient for 50 to 250 keV Protons Traversing Thin Solid Films" J.C. Eckardt.
XV INTERNATIONAL CONFERENCE ON THE PHYSICS OF ELECTRONIC AND ATOMIC COLLISIONS, Brighton, England, 1987: - 13 -
"Calculation of the Electron Emission on the Ridge in Proton-Helium Collisions" M.L. Martiarena, A. D. Gonzalez, C.R. Garibotti, D. H. Zanette.
"A Theoretical Model for Ionizatlon in Ion-Atom Collisions. Application for Impact of Multicharged Projectiles in Helium" P.D. Fainstein, V.H. Ponce, R.D. Rivarola.
"Three-Particle One-Dimensional Models. Excitation and Capture" J.i£. Miraglia, V. Rodriguez, M.S. Gravielle, V.H. Ponce.
- FRUHJORSTAGUNC DER SCWEIZERISCHEN PHYSIKALISCHEN GESELLSSCHAFT, Zurich, Switzerland, 1987:
"Change of Surface Magnetism Induced by Ar - Sputtering of Fe O " M. Aeschlimann, G.L. Bona, F. Meier, M. Stampanoni, G. Zampieri.
"Magnetic Surface Properties of Amorphous TbFe- Films" M. Aeschlimann, G.L. Bona, F. Meier, M. Stampanoni, G. Zampieri, H.C. Siegmann.
- EUROPEAN CONFERENCE ON SURFACE SCIENCE, Luzern, Switzerland, 1987:
"Ferromagnetism of Thin Epitaxial fee Cobalt and fee Iron Films on Cu (001) Observed by Spin-Polarized Photoemisslon" M. Stampanoni, D. Pescia, G. Zampieri, G.L. Bona, A. Veterlaus, F. Meier.
4.1.2. Domest i c Conferences:
71a REUNION DE LA AFA, Córdoba, October, 1986:
"Decaimiento Temporal de Singularidades en Soluciones de la Ecuación de Boltzmann" D.H. Zanette, M.L. Martiarena, C.R. Garibotti.
"Decaimientos Potenciales en Soluciones de la Ecuación de Boltzmann" D.H. Zanette, C.R. Garibotti.
"Entropía del No Equilibrio para un Gas Diluido" D.H. Zanette, C.R. Garibotti.
"Emisión Electrónica en Condiciones de Incidencia Rasante de Protones de Superficie" L. de Ferrari is, R.A. Baragiola.
"Plasmones en el Espectro XPS de Ar y K Implantadas en Al" M. Abbate.
"Producción de Electrones por Transmisión de H y H en Láminas Delgadas de D y Al en el Rango de Energías de 10 a 100 keV" E. Sánchez, L. de Ferrari is.
"Desplazamiento con el Ángulo do la Energía a que se Produce el Máximo Frenamiento de Haces Iónicos" M. M. Jakas, G. Lantschner, J.C. Eckardt. - 14 -
"Pérdida de Energía de Partículas en Sistemas Atómicos Confinados: Efectos Cuánticos y Térmicos" N.R. Arista, A. R. Piriz.
"Modelo de Cas de Electrones Inhomogéneos para Describir la Pérdida de Energía de Partículas en Sólidos" N.R. Arista.
- 72a REUNION DE LA AFA, Barí loche, September, 1987:
"Distribuciones noblemente Diferenciales de Electrones Eyectados de IFIH Superficies; de Entrada y Salida de Haces Iónicos en Láminas de Carbono" S. Suárez, G.C. Bernardi, P. R. Focke, W. Meckbach.
"Producción de Electrones Convoy por Transmisión de H (60 keV) en Láminas Delgadas de Aluminio. Dependencia con las Condiciones Superficiales" F.. A. Sánchez.
"Electrones Convoy Producidos en Colisiones de Pérdida dentro del S6J ido" P.H. Focke, R.O. Barrachina, W. Meckbach.
"Forma de los Espectros de Pérdida de Energía de Protones que •M r;iviesan Láminas Delgadas" N.K. Arista, N.E. Capuj, C. Lantschner, J.C. Eckardt.
"Perdida de Energía cié Iones que Atraviesan Laminas Delgadas Inhomogéneas" N.K. Capuj, M. M. Jakas.
"Orden Ferromagnético en Monocapas de Co Evaporadas sobre Cu (001)" D. Pescia, M. Stampanoni, G. L. Bona, R. F. Willis, F. Meier, i"., /ampieri.
"Estudio de Fenómenos Magnéticos Mediante Fotoemisión con Análisis de Spin y Resolución Temporal" <;. 1.. Bona, F. Meier, G. Schonheuse, M. Aeschlimann, M. Stampanoni, H.C. Siegmann, G. Zampieri.
"Contribuciones Intrínsecas y Extrínsecas a la Producción de Plasmones on XPS" M. Abbate, N.R. Arista.
"Ionización de Helio por Impacto de Iones Altamente Cargados" P.D. Fainstein, V. H. Ponce, R. D. Rivarola.
"KfenLo:: de Segundo Orden en la Emisión de Electrones por Impacto de Ititics Desnudos sobre Blancos Neutros" l'.li. Kiiins-.Lt.-in, V.M. Ponce, R. D. Rivarola.
"¡Vininc-rión de Vacancias de Capa Te por Impacto de Núcleos sobro AL'ini'is" A. Martínez, K 1). Fainstein, G. Deco, R. 1). Rivarola. - 15 -
"Modelo Teórico para Ionización en Colisiones Ion-Atomo Multielectrónico: Ionización del Helio" P. D. Fainstein, R. D. RIvarola.
"Ecuación de Boltzmann Generalizada para Gases de Dos Velocidades" D.H. Zanette.
"Difusión No Lineal de Partículas en un Medio Dependiente del Tiempo" D.H. Zanette, R.O. Barrachina.
"Solución General de la Ecuación de Boltzmann para una Mezcla Binaria de Gases" M. L. Martiarena, R.O. Barrachina, D.H. Zanette.
"Análisis XPS de Compuestos de La-Sr-Cu-O" H. Ascolani, M. Guraya, M. Abbate, G. Zampieri, D. Esparza, C. D*Ovidio, M.T. Malachevsky.
"Producción de Electrones Convoy por Transmisión de H (60 KeV) en Láminas Delgadas de Al. Dependencia con las Condiciones Experimentales" E. A. Sánchez.
4.1.3. Invited Communictions:
Xílt.h INTERNATIONAL CONFERENCE ON ATOMIC COLLISIONS IN SOLIDS (ICACS), Okayama, Japan 12 - 16 October, 1987:
"Beam Foil Convoy Electrons and their Possible Origin" W. Meckbach.
INTERNATIONAL SYMPOSIUM ON DYNAMIC INTERACTION OF CHARGED PARTICLES WITH SOLIDS, Wako-shi, Saitama, Japan, 8-9 October, 1987:
"Experimental Aspects of Measurement of Atomic Projectile Induced Electron Distributions" W. Meckbach.
X REUNIAO DE TRABALHO SOBRE FÍSICA NUCLEAR, Sociedad Brasileira de Fisica, Caxambú, Brazil, 1987:
"Interacción de Iones en Sólidos y Plasmas" N.R. Arista.
3rd WORKSHOP ON HIGH-ENERGY ION-ATOM COLLISION PROCESSES, Debrecen, Hungary, 1987:
"Electron Emission at Small Angles in H -He Collision" C.R. Garibotti.
IX INTERNATIONAL SEMINAR ON ION-ATOM COLLISIONS, Frankfurt, Federal Republic of Germany, 1987:
"Angular Distribution of Electrons Emitted in H -He Collision" C.R. Garibot.ti. - 16 -
II TALLER LATINOAMERICANO DE FÍSICA DE PLASMA, Medellín, Colombia, 1987:
"Teoría de Respuesta Dieléctrica de Plasmas Cuánticos" N.R. Arista.
"Interacción de Partículas con Plasmas Densos" N.R. Arista. - 17 -
4.4. Publications:
"OBSERVATION OF A NEW ATOMIC-LIKE PEAK IN THE ION-INDUCED AUGER SPECTRUM OF Si" L. de Ferrari is, 0. Grizzi, G. Zampieri, E.V. Alonso, R. A. Baragiola. Surface Science 167, L175 (1986).
"M NN AUGER EMISSION OF K EXCITED WITH LOW ENERGY Ar( + ) AND K( + ) PROJECTILES" G. Zampieri, R. A. Baragiola. Physical Review B33, 588 (1986).
"IMPACT-PARAMETER DEPENDENCE OF THE ELECTRONIC ENERGY LOSS OF PROTONS IN COLLISIONS WITH ATOMS" H. Ascolani, N.R. Arista. Physical Review A33, 2352 (1986).
"KINETIC ELECTRON EMISSION FROM SOLIDS INDUCED BY SLOW HEAVY IONS" E. V. Alonso, M. A. Alurralde, R. A. Baragiola. Surface Science 166, L155 (1986).
"COINCIDENCE EXPERIMENT CONCERNING THE ORIGIN OF CONVOY ELECTRONS PRODUCED BY SWIFT DEUTERIUM BEAMS TRAVERSING CARBON FOILS" M.G. Menéndez, M. M. Duncan, S.D. Berry, I. A. Sellin, W. Meckbach, P.R. Focke, I.B.E. Nemirovsky. Physical Review A33, 2160 (1986).
"A COMPARISON BETWEEN MULTIPLE INTERACTION COMPUTER SIMULATIONS AND THE LINEAR THEORY OF SPUTTERING" M. M. Jakas, D. E. Harrison, Jr. Nuclear Instruments and Methods B14, 535 (1986).
"ADIABATIC LIMIT FOR THE TIME DEPENDENT COULOMB PROBLEM" M. V. Ganduglia, V.H. Ponce. J. of Chemical Physics 84, 3324 (1986).
"ITERATIVE SOLUTION OF BOLTZMANN EQUATION" D. H. Fujii, R.O. Barrachina, C.R. Garibotti. J. of Statistical Physics 44, 95 (1986).
"CONTINUUM EMISSION DURING ION-ATOM COLLISION AT HIGH PROJECTILE ENERGIES" A.D. González, J. E. Miraglia, C.R. Garibotti. Physical Review A34, 2834 (1986).
"TEMPERATURE TRANSFORM OF BOLTZMANN EQUATION" R.O. Barrachina, D. H. Fujii, C.R. Garibotti. J. of Statistical Physics 45, 541 (1986).
"DIFFRACTION OF LOW ENERGY ION INDUCED SECONDARY ELECTRONS EMITTED IN THE FORWARD DIRECTION FROM A SOLID FOIL" A.R. Goñi, S. Suarez, P.R. Focke, G.C. Bernardi, W. Meckbach. Physical Review Letters 57, 3584 (1986). - iH -
"FFFF.CTS HI-' THE UANNIER RIDGE ON SECONDARY ELECTRON SPECTRA IN I'¡*OTON-HL- HIM COLLISIONS" W. Moi-kbu-h, P. R. Focke, A. R. Gofii, S. Suarez, J. Macek, M. C. Meriende?. !;hy:;ica! Review Letters 37, 1587 (1986).
"AN1SOTROP1C APPROACH TO EQUILIBRIUM IN THE NONLINEAR SPATIALLY HOMOGENEOUS ISOLTZMANN EQUATION" R. 0. Barrat-hina, C.R. Caribotti. Rarefied Cas Dynamics, Ed. by V. Boffl, C. Cerclgnami (Teubner, St.iitt.tfiirl., 19815) Vol. 1, pp 10.
"ITKKATION SCHEME FOR THE SOLUTION OF THE NONLINEAR SPATIALLY HOMOGENEOUS BOLTZMANN EQUATION" li. II. Fuji i , R.O. Bar-rachina, C.R. Garibotti. Ikurfied (¡as Dynamics, Ed. by V. Boffi, C. Cerignami {Teubner, Slul.lgart., 1986) Vol. 1 pp 514.
11 Ni >N I SÜTROPIC SOLUTIONS OF BOLTZMANN EQUATION" li.i) Barrarhina, C.R. Caribotti. .). i,f Statistical Physics 45, 467 (1986).
".AM hi.i-:CTKON CAS APPROACH TO THE ENERGY LOSS OF CHARGED PARTICLES IN SOI.iDH: THÍ-: CONFINED ATOM MODEL" N.H. Arista i <.! Physirs CH3, 1.811 (1986).
"i.l.KCTRON EMISSION IN PROTON BEAM SURFACE INTERACTION AT GRAZING ÍNÍ. IDENCF." !.. de Forrar-iis, R. A. Baragiola. I'hyHk-al Review A33, 4449 (1986).
"BEAM FOIL CONVOY ELECTRON IMUBLE DIFFERENTIAL DISTRIBUTION FOR nn-riDO keV PROTONS INCIDENT ON CARBON FOILS" I'.K. Focke, W. Meckbach, I. Nemirovsky, G. C. Bernardi. Nucli-ai- Infitruments and Methods BÜ, 314 (1986).
"I-.FI--F.CT OF ION BOMBARDMENT ON THE SURFACE MAGNETISM OF Fe O " 3 4 M. Aoschl imann, G. L. Bona, F. Meier, M. Stampanoni, G. Zampieri, II. Siej'mann. Applied Physics Letters 49, 824 (1986).
"ANALYSIS OF A SECONDARY ELECTRON EMISSION IN BEAU FOIL EXPERIMENT WITH MOLECULAR IONS" N.R. Arista, M. M. Jakas, G. Lantschner, .l.C. Eckarc?-. i'liysica] Review h'M, 5112 (1986).
"SPIN POLARIZED PH0T0EM1SSI0N FROM IRON BY PULSED LASER RADIATION" • ,.!.. Bona, F. Meier, C. Schonhense, M. Aeschlimann, M. Stampanoni, (;. Xampicri , H. Siegmanr,. Phyo ic-.il Review H'M_, 77S4 (1986).
"I-.NI.I«;Y LOSS AND STRAGGLING OF CHANNELED PROJECTILES BY TNNER SHELL ;-:i.i-:ri RUNS" :•;.(,'. GoJdbf.Tg, V. )•!. Ponce. Radiation Effects l_00, 139 (1986). "THE USE OF ELECTRON TRANSLATION PHASE FACTORS IN LOW ENERGY ATOMIC COLLISIONS" V.H. Ponce. Nucleares (I.A.N. Colombia) N°l, 47 (1986).
"JON INDUCED RIDGE ELECTRONS AND THEIR DIFFRACTION IN SOLID FOIL TARGETS" A.R. Goñi, W. Meckbach, S. Suárez, P. R. Focke, G.C. Bernardi. /.. für Physik D4, 253 U987).
"SYMMETRIC EIKONAL MODEL FOR ION1ZATION IN ION ATOM COLLISIONS" P.D. Fainsteín, R. D. Rivaróla. J. of Physics B20, 1285 (1987).
"UNITED-ATOM LIMIT OF RADIAL COUPLINGS BETWEEN MOLECULAR WAVEFUNCT1ONS" A. Marcías, A. Riera, P. J. Salas, V.H. Pouce. J. of Physics B20, 295 (1987).
"DO SOLID SURFACES POTENTIAL BARRIERS RETARD CONVOY PEAK ELECTIONS?" S. Suárez, A.R. Goñi, W. Meckbach, P. R. Focke. V.. fur- Physik D6, 55 (1S87).
"ENERGY LOSS DISTRIBUTIONS OI~ 50-26 keV PROTONS TRAVERSING THIN SOLID FOILS: DETERMINATION OF THE SKKWNKSS COEFFICIENT AND INFLUENCE OF FOIL ROUGHNESS" N.K. Capuj, .J.C. Eckardl, G. Lantschner. N. R. Arista. Physical Review A36, 3715 (1987).
"NOB1.K f;AS ION SPUTTERING YIELD OF GOLD AND COPPER: DEPENDENCE ON THE ENERGY AND ANCLE OF INCIDENCE OF PROJECTILES" A. Oliva-Florio, R. A. Biiragiola, M. M. Jakas, E.V.Alonso, J. Ferrón. Physical Review B35, 21S8 (1987).
"ENERGY LOSS OF FAST PARTICLES IN CONFINED ATOMIC SYSTEMS AT VERY HIGH TEMPERATURE" N.R. Arista, A.R. Piriz. Physical Review A35, 3450 (1987).
"POWER-LAW DECREASING SOLUTION OF THE BOLTZMANN EQUATION" D.H. Zanette, C. R. Garibotti, R.O. Barrachina. Physics Letters A120, 219 (1987).
"AUGER ELECTRON EMISSION FROM Al INDUCED BY keV Ar BOMBARDMENT EXPERIMENTS AND MONTE CARLO SIMULATION" 0. Grizzi, R. A. Baragiola. Physical Review A35, 135 (1387).
"ION INDUCED DESORPTION OF OXYGEN FROM SOLID SURFACES" E.V. Alonso, G. Zampieri, M. Abbale, 0. Grizzi. J. of Nuclear Materials L44. 287 (1987).
"APPLICATION OF DISTORTED WAVE MODELS FOR ELECTRON EMISSION IN ION-ATOM COLLISIONS" R. D. Rivarola, P.D. Fainstein. Nuclear Instruments and Methods B2A/2H, 240 (1987). 20 -
"KERROMAGNETISM OF THIN EPITAXIAL fee COBALT FILMS ON Cuinn OBSERVED BY SPIN POLARIZED PHOTOEMISSION" I) IVscia, G. Zampieri. M. Stampanoni, G. Bona, R. Willis, F. Meier. Physical Review Letters 58, 933 (1987).
"CHANGE OK SURFACE MAGNETISM INDUCED BY Ar+-SPUTTERING OF Fe O " 3 4 M. Aeschlimann, G.L. Bona, F. Meier, M. Stampanoni, G. Zampieri. Helvetica Physica Acta 60. 794 (1987). "MAGNETIC SURFACE PROPERTIES OF AMORPHOUS Tb Fe FILMS" M. Aeschlimann, G. L. Bona, F. Meier, M. Stampanoni, G. Zampieri, H.C. Siegmann. Helvetica Physica Acta 60, 792 (1987).
V.:i EFFECTS IN THE I0NI2ATI0N OF HELIUM BY ION IMPACT" P ¡'.0. KainsU;in, V. H. Ponce, R. D. Rivarola. Physical Review A36, 3639 (1987). "IJUURI.K DIFFKRENT1A1. DISTRIBUTIONS OF ELECTRONS EMITTED WHEN 170 keV l'l:f)T()NS INTERACT WITH A THIN CARRÓN FOIL" :;. Siiai-cz, W. Merkbaeh, Ci.C. Bernard!, P. R. Focke. / I'iji' Physik 1) (to be published).
"VARIATION OF PEAK ENERGY LOSS WITH ANGLE OF OBSERVATION" ¡;. l.;inl sclujcr, J.C. Kck;¿i-dt, M. M. Jakas, N. P.. Capuj, H. Ascolani. Physical Review A (to be published).
"A THF.ORITICA!. MOW"! FOR I0NIZATI0N IN ION-ATOM COLLISIONS. APPLICATION FOR IMPACT i.1 MULTIC1IARGF.D PROJECTILES ON HELIUM" P.M. Ka.insl.ein, V. II. Ponce, R. IJ. Rivarola. J. of Physics B (to be published).
"NON-LINEAR PAKT1CI.K DIFFUSION IN A TIME DEPENDENT HOST MEDIUM" U.K. Zanette, R. 0. Barrachina. Physics of Fluids (to be published).
"TWO-VELOCITY GAS DIFFUSION WITH REMOVAL AND REGENERATION PROCESSES" 13. II. Zanette. Physica A (to be published).
"KKRROMAGNETISM OF THIN EPITAXIAL fee COBALT AND fee IRON FILMS ON Cu (001) OBSERVED BY SPIN-POLARIZED PHOTOEMISSION'1 M. Stampanoni, D. Pescia, G. Zampieri, G.L. Bona, A. Vaterlaus, F. Meier. Surface Science (to be published).
"DOUBLE DIFFERENTIAL SPKCTRA OF ELECTRONS EMITTED FROM THE FORWARD AND BACKWARD SURFACE OF A CARBON FOIL TRAVERSED BY A BEAM OF HYDROGENIC PROJECTILES" S. Suarez, G.C. Bernard i, P. R. Focke, W. Meckbach. Nuclear Instruments and Methods B (to be published).
"INELASTIC KNLRGY LOSSES IN CASCADES AND THE THEORY OF ATOM EJECTION" I). K. Harrison, Jr., M. M. Jakas. Nuclear Instruments and Methods (to be published). - 21 'ill
"THE COMPUTER SIMULATION OF ATOMIC COLLISIONS IN SOLIDS" R. Webb, M. M. Jakas, D.E. Harrison, Jr. Nuclear Instruments ana Methods (to be published).
"ENERGY LOSS AND STRAGGLING OF CHANNELED PROJECTILES BY INNER SHELL ELECTRONS" B.C. Goldberg, V. H. Ponce. Radiation Effects (to be published).
"INSTRUMENTAL EFFECTS ÍN MEASUREMENTS OF ELECTRON DISTRIBUTIONS INDUCED BY ATOMIC COLLISIONS" G.C. Bernard!, P.R. Foclce, S. Suárez, W. Meckbach. Nuclear Instruments and Methods (to be published).
"ANGULAR DISTRIBUTIONS OF ELECTRONS EMITTED IN PROTON-HELIUM COLLISIONS" G.C. Bernardi, P.R. Focke, S. Suárez, W. Meckbach. Nuclear Instruments and Methods (to be published).
"CALCULATED CONVOY ELECTRON DISTRIBUTION DUE TO ELECTRON LOSS COLLISIONS INSIDE SOLID TARGETS" R. 0. Barrachina, A. R. Goñi, P.R. Focke, W. Meckbach. Nuclear Instruments and Methods (to be published). - 23 -
LOW TEMPERATURE PHYSICS
1. STAFF
Scientists Technicians
D. Castello + A. Arriberre L. Civale + R. Fuentes + F. de la Cruz R. Scotti M. E. de la Cruz S. Trochine P. Esquinazi * H. Tutzauer .1. ftuimpel ++ J. Luzuriaga IB Graduate R. Maiztegui # Students E. Martinez G. Nieva + R. Decca M. Nunez Regueiro * C. Duran E. Osquiguil ++ K. Hallberg J. Sereni ° A. Izbizky H. Safar
CNEA/CONICET Researcher + CNEA Fellow ++ CONICET Fellow ° von Humboldt Fellowship (1986/87) °° SECYT Fellow * Under contract to ALTEC 2. GENERAL DESCRIPTION
Over the years this laboratory has developed its own cryogenic
equipment as well as basic infrastructure for a sample preparation
laboratory.
2.1. Facilities:
To accommodate more equipment our facilities were relocated and
expaniji-ii iliji-liiK Mu- 1ÍIH11 1 !)H7 period.
The following contributions of new equipment were received as
part, of oxlijl. lnji Cooperation Agreements:
- Federal Republic of Germany: Ultrasonic equipment which is al"eady
operating.
- France: A cryostat for the measurement of transport properties
between 1.5K and 400K.
- Sputtering equipment, which has already been calibrated. It is now
being adapted for production of superconductor
structures.
We have also strengthened our on line data acquisition
capabilities with several aditional personal computers and
peripherals.
Since February 1987, a substantial effort has been devoted to
research in ceramir superconductors with samples supplied by the
Magnetic Resonance and the Research and Development Divisions of the
Centro Atómico Buriloche. A program is under way to develop thin foils from these superconductors. Also in connection with this area of research the Laboratory has organized a literature search and reprint exchange library available to the Centro Atómico staff as well as the other laboratories interested in the subject.
Cryogenics: This section, a part of the Low Temperature Division, produces liquid helium, air and nitrogen to fulfill the requirements oT laboratories at the Centro Atómico Bariloche and those of other
laboratories in the area (INVAP, INTA). In 1987 the Laboratory purchased a liquid nitrogen machine with a 30 £/hour production and a
:(000 t. storage tank. The facilities will be put into operation in
I'.WH.
V..'¿. Cooperation Agreements:
Amorphous sampler were made for the angular correlations laboratories at the Physics Departments of the Universidad Nacional de
La Plata and the School of Engineering of the Universidad de Buenos
Aires.
The Laboratory received financial assistance from CONICET. The
KTF gave grants to Drs. P. Esquinazi, M. Nunez Regueiro and
J. I.uzuriaga.
Scientific cooperation agreements with CNRS-CRTBT, Grenoble,
France; Heidelberg University, Germany and the Materials Science and
Kleotrical Engineering Jopartmonts of the University of California at
O.'ivi:;, have continued. - 27 -
2.3. Conferences:
The staff of the Division participated in several International
Conferences as attendants, guest speakers and contributing papers.
- "INTERNATIONAL CONFERENCE ON ANOMALOUS RARE EARTHS AND ACTINIDES",
Grenoble, France, 7-11 July, 1986.
- "ADRIÁTICO RESEARCH CONFERENCE ON HEAVY FERMION SYSTEMS", Trieste,
Italy, 15-19 July, 1986.
- "ALEXANDER VON HUMBOLDT TAGUNG", Aachen, Federal Republic of
Germany, 6-9 October, 1986.
- "NEW DIRECTIONS IN LOW TEMPERATURE PHYSICS", Los Alamos, NM, U.S.A.,
20-21 October, 1986.
- "SEMICON 86", Buenos Aires, Argentina, 8-13 December, 1986.
- "FRÜH-JAHRSTAGUNG VON DER DEUTSCHEN PHYSIKALISCHES GESELLSCHAFT",
Münster, Federal Republic of Germany, March 1987.
- "THE EMRS CONFERENCE - MEETING ON SUPERCONDUCTING MATERIALS WITH
HIGH TRANSITION TEMPERATURES", Strasbourg, "r-ance, June 1987.
- "ALEXANDER VON HUMBOLDT TAGUNC", Bonn, Federal Republic of Germany,
July 1987. - 28 -
- "WORKSHOP ON CHARGE DENSITY WAVES", Aussois, France, September 1987.
- "1987 FALL MEETING", Materials Research Society, Boston, Mass.,
U.S.A., 30th November to 5th December, 1987. - 29 -
:i. RESEARCH PROGRAMS
A. Amorphous Metals
1) A change of dimensionality in the behavior of vortices in
amorphous Zr Cu has been observed. Through this change from two to
three dimensions the first experimental determination of the pinning
force range has been achieved.
Kxperiments to determine the angular dependence of the collective
regimes were performed. The results obtained up to now for a three
dimensional regime showed that the collective pinning disappears when
the surface pinning increases with the angle between magnetic field
and surface sample decreasing. The bidimensional regime shows an
angular dependence inducing a change of dimensionality for small
angles. The boundary conditions imposed by the sample surface in both
regimes are now under- study.
2) Measurements on superconductors by means of the vibrating reed
technique have begun within an Argentine-German cooperation program.
The dilution refrigerator was put into service and the
thermometer was calibrated. The necessary auxiliary parts for sample
mounting the coaxial cables were installed and the completed facility
now permits measurements down to temperatures of 0.07K and with
magnetic fields of up to 50KOe. Using this experimental setup:
- Low temperature acoustic properties of Zr Cu amorphous alloy were 70 30 studied, with particular attention to their evolution with - •)() -
annealing. Results were interpreted within the framework of the Two
Level System (TLS) moael and two features should be remarked: a) The
decrease in attenuation; the increase in thermal conductivity and
the change of the temperature dependence of the sound velocity
observed upon annealing are due mainly to a change in the coupling
constant between phonons and TLS; b) The electron TLS interaction is
different from that predicted by theory.
- Using the vibrating reed with a magnetic field applied parallel to
the roed, the elastic coupling constant of the flux line lattice to
the material was measured in amorphous Zr Cu . In an as quenched 70 30
sample, the measurements are in agreement with those obtained from
critical current experiments done previously in the group. Upon
annealing, results indicate that a low critical temperature (T <1K)
phase may be growing in the sample surface.
3) Measurements of the magnetic flux enclosed in superconducting amorphous Zr Cu in the Meissner state or in the mixed state have r 70 30 been performed using a SQUID.
The quantized penetration of flux as vortices is a characteristic of the mixed state. These vortices can be treated as interacting particles when the density is a function of temperature and external magnetic field. In general the results were obtained sweeping temperature at constant external magnetic field. The observed irreversibi1 ities indicate the existence of pinning forces in the dei'ects of the bulk as well as the presence of a surface barrier. - '¡I -
When the magnetic j"ield is low enough, the entrance and exit of
the vortices can be inaividually detected, which means that in this
range collective movements have disappeared. In this high dilution
limit (non interacting vortices) the influence of the surface barrier
and defects on one vortex can be studied. The experimental
observations showed an anomalous decrease of magnetic flux at constant
field and increasing temperature. This result has been interpreted as
the permanence of the system in a particular non-equilibrium quantum state characterized by the number of vortices.
ÍSomc- measurements of the flux variation as a function of time,
induced by the "flux creep" phenomenon, at fixed temperature and applied field have also been made. Preliminary results show
logarithmic dependence with time, in agreement with theoretical predict ions.
B. Superconducting Muít i layers:
We have worked on samples of superconducting multilayers. These consist in periodic arrangements of layers of two different materials, one superconducting and the other normal. In our case the super-conducting material is Nb.
The size effect on the critical temperature, perpendicular critical field and resistivity was studied in Nb/Af multilayers. The results can be qualitatively understood as a change in the electronic density of states with constant diffusion coefficient. It is possible to propose several mecaanisms for this behavior. One is based or. variations of the electronic lifetime. Another is the size effect - !2 -
described by a weak localization theory. Still another is a
modification on the boundary conditions in the Ginzburg Landau theory.
The parallel critical field follows the Ginzburg Landau theory
for samples of thickness comparable to the coherence length. As the
thickness increases, theoretical predictions start deviating from the
experimental results. These cases show a temperature dependence which
is neither linear nor square root, as in a homogeneous sample.
The angular dependence of the critical field shows sharp peaks
near the parallel orientation. in no case have we observed the
fiuiKiod maxima predicted by the Lawrence and Doniach theory.
Over H secies c,v Nu/Cu multilayers provided by Dr. I.K. Schuller,
Argonne National Lab. J.S.A., we measured the magnetization of the
superconducting state. The -¡ampies all have l^tm thickness but the
periods- ranged from 10A to ii') A. The results show that the behavior or these materials is well described by a superconducting penetration depth. This penetration depth is in excellent agreement with an extrapolation of the microscopic theory of superconductivity in homogeneous and isotropic materials.
The vortex contribution to the flux expulsion shows structure as a function of applied magnetic field. This structure was explained in terms of a model including vortex-vortex and vortex-surface repulsion.
The existence of a finite field for complete expulsion of vortices war; established. This field i s different from zero due to the fact
that the sample thickness is comparable to the penetration depth. - 33 -
In the model the structure in the magnetization vs. field curve
is interpreted as a dimensional transition in the vortex lattice. In a sample of thickness comparable to the penetration depth the vortices
interact repulsively among each other and with the surfaces. This
interaction tends to align them in the center of the sample. As the density of vortices grows, the repulsion between them becomes stronger until the row splits into a bidimensional lattice. This model can be adjusted to the data without free parameters.
C. Low Dimensional ity:
Study of transport properties of low dimensional systems: A cryostat for transport measurements between 1,5K and 400K (brought by a French expert) was put into operation. The experiments are to verify whether resistivity saturation is adequately explained by the phenomenological theory based on molecular states.
Lie. Dario Castello continued work on his doctoral dissertation with the construction of an apparatus for measuring the resistivity of samples under external strain. We have also measured the behavior of the 1-D compound NbSe under high pressure (80Kbar). This experiment was done partly during the visit of Dr. M. Nunez Regueiro to. Grenoble and of Dr. J.M. Mignot to Bariloche, within fhe Argentine-French cooperation program. As a consequence of this collaboration a new field of research, that of high pressures, becomes available for the
Centro At6mico, and the Low Temperature Division will be able to measure resistivity between IK and 300K up to 100 Kbar of pressure.
For the small pressure range (1 to lOKbar) a piston cell has been orderec, using the Third World Academy grant of M. Núñez Regueiro.
U. intermedíate Valence and Heavy Fermi on Systems:
We have studied rare earth and actinide compounds, which show the characteristic behavior of heavy fermion systems, using the specific heat technique. The interest of such a study was to recognize the main feature:; of the transition from an Intermediate Valent (IV) to a
,:::ij;netic or to a Kondo ¿round state.
in the CePd W compounds, where H are the B and Si i ni crst i I. i nls, it was possible to compare both kinds of transitions
\.'M hin the same environment. With addition of B, there is a
I .runs i t. ion from the IV .round state of Ce, in CePd , to a concentrated
Kondo one. In the case of Si the transition leads to a magnetic state. In both cases an i ni ermediate state, due to Ce magnetic clusters, was detected. We have also found anomalous behavior in the thermal excitations of the Ce crystal field levels. Further measurements of specific heat under applied magnetic fields up to 3
Tes la, confirmed the Kondo-like and the magnetic behavior induced by B and Si interstitials respectively.
The Ce Ni Pd pseudoternary alloy appeared to be a good example of a ferromagnetic Kondo-dense system, for low x values. We have verified the predicted competition between the magnetic exchange interactions and the Kondo effect. From the temperature dependence of the entropy gain, we have found that only a doublet crystal field ground state is involves in the Kondo singlet state formation. - 35 -
This research pro;\ram is part of a cooperation project, with the
I.MSFS of the University of Strasbourg (France). During the visit of
Dr. J. Sereni to those laboratorios preliminary studies on the Ce Rh X I'd system were carried out. l-x
The specific heat measurements on Tb impurities diluted in a Th supnrconducl. ing matrix were complemented with magnetic susceptibility measurements at the University of Cologne (W. Germany). These studies confirmed the instability of the 4f shell of Tb in that matrix. At Tb concentra!, ions higher taan 10% the alloy behaves as a spin glass-like system.
K. Vi brat i n;?. Reed Technique:
1) IJy submerging the vibrating reed in helium the superfluid transition may t*r ::>'iiii-d. Results can be interpreted by means of the two-fluid model and classical fluid mechanism.
'¿) By using deled ion and driving electrodes made of different superconducting materia.s in the vibrating reed, the behavior of tl.ose materials could be studied. It is possible to interpret the results by assuming that vortices penetrate the electrode and are subsequently pinned. With this technique it might, be possible to measure H , and pinning forces in a sample deposited on the electrodes.
I'. Ceramic Superconductors:
1) Experimental results on the superconducting and normal properties of Ba(PbBi)O were analyzed and interpreted in collaboration
with •• ¡enlists at. the- . ¡n i v«.-r -s i dad de Buenoti Aires. It was shown that
the dí;gree of elect.r-i.jal connectivity between the grains can be
control !ci through t h«..-rm;il treatment. This mechanism makes it
possible to control the effective JnLergrain interaction that produces
a coherent phase transition.
y.) Since l-Y-bruary 1JSJ7 a big effort has been made in the Low
Temperature Lab to app,y hij;h T ceramic superconductors. Research was carried out on the following subjects: :i) ¡ili.'ct.rical resist i vi ...y, magnetic flux expulsion and lower critical field measurements, performed in t.he l.a Sr ^ Cu O system for di f feri'n!. heal treatments. The results obtained stressed the í-ranulíií" oharacti-r n¡' the system. A simple.' model to Luke iiitu account the temperature and magnetic field dependence of i.he magnetization curves. Within this model it is possible to estimate the critical current values. The irreversibi1 ity of the magnetization curves, even in the presence of very low magnetic fields, indicates that the behavior of the material is that of an inhomogeneous superconductor. The influence oí' oxygen content1, of i.he samples on the resistivity and magnetization. The resistivity turns out to be linear in T at high temperatures (up to 800K) and to have semiconducting-!ike behavior at low t.emperal 'ires. - 37 - Detailed electrical resistivity measurements,performed on samples of La Sr Cu O in a wide range of temperatures (4K to 1.8 Ü.V. 4-y 1000K) as a function of heat treatment in vacuum and in 1 Atm of oxygen at 550K. The resistivity of this material changes reversibly by more than two orders of magnitude with variations of oxygen content of less than 1%. Using the fact that the resistivity does not saturate at high temperatures a lower limit for the value of the electronic mean free path has been estimated. As -A consequence of this analysis it has been established that t.hr;;-;e materials are high K superconductors in the clean limit. II. has been observed that the oxygen content of the material controls- u transition from a metallic regime at high temperatures where I.ho resistivity is linear in T to a localized one at low temperature;;. The low temperature regime has been interpreted in terms of the Variable Range Hopping model. (conduction by localized electronic states near the Fermi level). b) The thermal conductivity of both La Sr Cu O and RBa Cu O l-x x 4-y 2 3 7-x (where H is a rare earth) systems was measured. It was found that al 1 these compounds show a neat. T dependence at low temperatures (1.ü been interpreted by assuming the existence of tunneling systems (TS). Phonon scattering against these systems must give a mean free path varying as of , where o> is the phonon frequency and hence a T dependence. The existence of TS can also explain naturally the behavior of sound attenuation and the linear term of the specific heat at low temperature. On the other hand from the behavior of the phonon thermal conductivity below the - 38 - supi;•conduct ing I.run.¿i t ion temperature we have been able to obtain the I emperature dependence of the superconducting gap. The temperature gap is 2A(0) = 3.3+0.7 k T , which favours a weak D C coupling mechanism for high temperature superconductivity. c) The following proper-ties were studied by means of the vibrating reed technique: - Superconducting critical field H in l,a Ba Cu O with 1 ^ Cl l.B 0.2 4 different values of oxygen content. II in KuHn Cu O . el :: :i 7 Sound velocity and attenuation in different ceramic superconductor:; in the 0.1 to 1S0K temperature range. - Magnetisation and pinning ¡'orces in La Sr Cu 0 . c ' r> 1.8 0.2 4 I-rom these measurements the following results are to be emphasized: The vibralinj' rood technique is adequate for measuring H and pinning forces in superconducting ceramics. There i;; evidence for the oxiKt^nrc of two-level systems, similar to those found in glasses in high T superconducting ceramics. - There ;ire anomalies in sound velocity and attenuation. Sr' l"u 0 was measured in a semi-adiabat ic calorimeter. An o. v. 1 anomaly associated with the superconducting transition was observed. Using tho two-fluid model, we obtain a value for the Sommerfcld cooficient which is five times larger than that predicted by the band calculations. We have also measured the non-superconducting compound La Cu O intending to use it as a matrix for thermal excitations. Because of their different structural characteristics, reflected in a different, phonon spectrum, we concluded that La Cu O is not an appropriate reference compound. For both superconducting and non-superconducting compounds a linear term in the specific heat, was observed. In this case its microscopic origin is still controversial. In cooperation with the Magnetic Resonance group, the low t.(.-mjf)cral.ure specific heat of the high temperature superconductors (RK) Ha. Cu 0^ (with RE = Gd, Dy) was measured. A magnetic ordering a* T = 2.2 and 0.91K was detected for Gd and Dy respectively. This study was complemented by magnetic susceptibility, KPK and electrical resistivity measurements, performed at. the Magnetic Resonance Laboratory. These measurements evidentiated a certain instability in the superconducting properties due to the presence of magnetic moments. Within t.he same cooperation program, the low temperature calorimiHrie study of Gd Ku lía Cu 0 is currently in x 1 -x ?. 3 V * progress. For low Gd concentrations, the Schottky anomalies originated in the ground st.atn crystal field splitting are observed. At high concentral ions, the temperature of the maximum - 40 - of the magnetic specific heat contribution increases linearly with x as is characteristic for spin glass systems. 4. CONFERENCES AND PUBLICA IONS 1.1. Conferences: 4.1.1. International Conferences: D.P.G., Freudenstadt, Federal Republic of Germany, April, 1986: "Akustiche Untersuchongen von Araorphem PdZr und CuZr in Supraleitenden und Normalen Zustand" P. Ksquinazi. H. M. Ritter, H. Neckel, G. Weiss. INTERNATIONAL. CONFERENCE ON ANOMALOUS RARE EARTHS AND ACTINIDES, Grenoble, France, 7-11 July, 1986: "Anomalous Crystal Field Effects in Ce-Heavy Fermion" J.G. Serení, G. Nieva, J.P. Kappler. "Anomalies of Dilute Terbium in Thorium" J.G. Sereni, G. Nieva, E. Braun, F. Oster, E. Brück, B. Roden, D. Wohlleben. - V INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER, Urbana, 111., U.S.A., August, 1986: "Acoustic Studies of Amorphous PdZr in the Normal and Superconducting State" S. Hunk linger, P. Esquinazi, H. M. Ritter, H. Neckel, G. Weiss. 18TII INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS, Kyoto, Japan, 20 - 26 August, 1987: "Flux Line Pinning in a Superconducting Vibrating Reed" P. Esquinazi, E. II. Brandt. WORKSHOP ON CHARGE DENSITY WAVES, Aussois, France, 19 - 24 September, 1987: "F.iToct of Local CDW Instabilities on the Properties of Metals: Phenomenology of the kesist ivi t.y, Magnetic Susceptibility, Thermal Conductivity and Behaviour with Irradiation Defects" M. Núñez Regueiro. "Effect of Local CDW on the Properties of Metals: A Simplified Exactly Solvable Model" G. Ortiz, M. D. Núñez Regueiro, M. Nunez Regueiro, B. Alascio. "Tunneling Systems in High Temperature Superconducting Ceramics" D. Castello, C. Duran, P. Esquinazi, A. Izbizky, J. Luzuriaga, G. Nieva, M. Núñez Regueiro. FALL MEETING, M. K. S , Boston, U.S.A. November 30 - December 5, 1987: - i a - "TIK; Cmnular Hehavior of l.aSrCuO: Oxygen Concentration Effects on the Eled.r1 i:al Hesistivity" I.. Civ;ilt?, E.J. Osquiguil, II. Safar, E.N. Martinez, F. de la Cruz, r;. I.. Nir.-vii, H. Di'cca. 4.1.2. Domestic Conferences: 71a RKUNION UK I .A AJ-'A, Córdoba, October, 1986: "EfVct.o Kondo y Orden Magnético en CeNi Pd (Oxl) X vi ~x) (,.!.. Nieva, J.G. Serení, J.P. Kappler, M. Afyouni. "Exponentos Críticos del Módulo de Young y de la Conductividad Eléctrica dt; I Queso Gruyere tridimensional" .). Sof'o, J. l.orenzana, E.N. Martínez. "I i.t.rzav: do I'inninp, y Defectos en Superconductores Amorfos Medidos a Través < i< - I na Corrientes Criticas" .1. l.uzuriaf»¡i. "Magnetización "fundiciones do Contorno en Anclaje Colectivo de Vórtices en ! ¡ii|x.-rcondut: lores Amorfos Tipo II" K.J. Osquiguil, F. ¡it- In Cruz, F..N. Martinez. "lleKunclajo de la Rot. dp Vórtices en el Régimen Colectivo: Un Comportamiento Cri t ico" F. di: la Cruz, K.J. Osquiguil, .i. I.uzuriaga, E.N. Martínez. TAn REUNION DF I.A AFA, Bar i loche, September, 1987: "Parámetros de Orden Inhomogéneo: Una Característica de la Superconductividad f;n Óxidos Cerámicos" J. Cu impel. I.. Civale, E. J. Osquiguil, E.N. Martínez, G. L. Nieva, F. de la Cruz. "1.a Transición Superconductora en La Sr CuO como Fenómeno ^ 1.8 0.2 4 Percolat ivo" E.J. Osquiguil, F. de la Cruz, E.N. Martínez. "La Lengüeta Vibrante en Helio Líquido: A Través del Punto Lambda" P. Fquinazi , .L Luzuria^a, E.N. Martínez. "AlRiinor; Comentarios y Apreciaciones sobre la Aplicación de Teorías de C-impo Medio a I ;i Superconductividad de Alta Te" F. dr; la Cruz. "Kfeetos de) Oxigeno on el Sistema LaSrCuO" E.J. OsquiRuil. C. Polín, C.I.. Nieva, L. Civale, R. Decca, M. H¡;nyaí:nr, F. "Superconductividad en ,:1 Sistema LaSrCuO en Función de Concentración de Sr" K. Hallberg, E.J. Osquiguil, L. Civale, M. Benyacar, F. de la Crux, D. Esparza, C. D'Ovidio, M.T. Malachevsky. "Mediciones Magnéticas en Superconductores Mediante una Cinta Vibrante" C. Duran, P. Esquinazi, J. Luzuriaga. "Anomalías en la Fricción Interna y Velocidad del Sonido de los Superconductores Cerámicos l.aSrCuO e YBaCuO" P. Esquinazi, J. Luzuringa, C. Duran. "Estado Fundamental a H = 0 del Superconductor Sinterizado LaSrCuO" L. Civale, H. Safar, F. de la Cruz, C. D'Ovidio, D. Esparza. "Comportamiento de Campos Críticos en el Sistema LaSrCuO" E.J. Osquiguil, K. Hallberg, F. de la Cruz, C. D'Ovidio, D. Esparza. "Calor Específico dol Superconductor I.a Sr CuO " H ' 1.8 .2 4 (;.!.. Nieva, K. N. Martínez, A. lzbizky, F. de la Cruz, D. Esparza, C. IVOvidio, M.T. Malachevsky. "Longitud de Penetración Superconduotora en Multicapas de Nb/Cu" J. Guimpel, F. de la Cruz, J. Murduk, I. Schuller. "Transición Dimensional en la Red de Vórtices de Multicapas de Nb/Cu" J. Guimpel, L. Civale, F. de la Cruz, I. Schuller. 4.3. Doctoral Dissertations: "Efectos de Tamaño en Superconductores Inhomogéneos" .1. Guiropel Scientific Advisor: F. de la Cruz (December, 1987). 4.4. Publications: "A SUPERCONDUCTING VIBRATING REED APPLIED TO FLUX-LINE PINNING. 1 - THEORY" E.H. Brandt, P. Esquinuzi, H. Neckel. .1. of [.ow Temperature Physics 63, 187 (1986). "A SUPERCONDUCTING VIBRATING REED APPLIED TO FLUX-LINE PINNING. 1! - EXPERIMENT" P. Esquinazi, H. Neckel, G. Weiss, E.H. Brandt. .1. of Low Temperature Physics 64., 1 (1986). "LOW TEMPERATURE THERMAL PROPERTIES OF CePd B SYSTEM" 3 x J.C. Serení, G.I.. Nieva, .). P. Kapplor, M. J. Besnus, A. Meyer. .1. of Physics i in, 435 (1986). "THE TUNNELING MOHI-.I. - INCOMPLETE FOR AMORPHOUS METALS" II. Neckel , I'. Esquinazi, G. Weiss, S. Hunklinger. Solid SI.aU' Communications 57, 151 (1986). "DRASTIC INCREASES OÍ-- FREQUENCY AND DAMPING OF A SUPERCONDUCTING VICRATING REED IN A i.or.;;iTui)lNAi. APPLIED FIELD" E. II. Isründt, P. Esquin^/.i, H. NeckeJ , G. Weiss. Physical Review Letters. SB, 89 (1986). "I MEAL TWO DIMENSK'f.M. KI.UX PINNING INDUCED BY ANNEALING IN SUPERCONDUCTING AMORP1U .,IS 7.V Rh " 7S 2S .1. Luzur¡rip,¡\, ('. O'Ovit.io, F. do la Cruz. Solid Sl.ia.tr- Communicat ions KV, i'.i'.i (1986). "HV/JÍ DEPENDENCE OF THE SUPERCONDUCTING CRITICAL TEMPERATURE AND FIELDS OF Nb/Al MULTILAYERS" J. Guimpel, M. E. de hi Cruz, F. de la Cruz, H.J. Fink, 0. Laborde, J. (.'. Vi 1 legior-. .1. of Low Temperature Physics QÜ. 151 (1986). "STRUCTURAL AND MAGNETIC PROPERTIES OF THE TERNARY RARE EARTH (RE) COMPOUND SERIES RE IN Au(2) (RE = La to Lu, Y)" M.J. Ucsnus, J.P. Kuppler, M.I'. Ravet, A. Meyer, R. Lahiovel, J. Pierre, E. Sifuid, CÍ. ... Niev;i, .I.G. Sereni. J. of Less Common Metals 120. 101 (1986). "DIMENSIONAL CROSSOVERS IN COLLECTIVE FLUX PINNING" E.N. Martinez, V. L. P. Frank, E.J. Osquiguil, F. de la Cruz. Solid State Communications 60, 151 (1986). "ACOUSTIC STUDIES OF AMORPHOUS PdZr AND CuZr IN THE NORMAL AND SUPERCONDUCTING STATE" S. Hunk linger, P. Esqui.iazi, II. M. líit.ter, H. Neckel, G. Weiss. V Int. Conf. on Pho..on Scattering in Condensed Matter, Ed. by A.C. Anderson and .J.I'. Wolfe, Springer Verlag 1986 (Berl in-Hcidelber-g). "ACOUSTIC EXPERIMENTS ON AMORPHOUS PdgfZrjf) AND Cu Zr?o IN THE SUPERCONDUCTING AND THE NORMAL STATE" P. Esquinazi, H. M. Ritter, H. Neckel, G. Weiss, S. Hunklinger. Z. für Physlk B64, 81 (1986). "SATURATION OF THE RESISTIVITY IN METALS WITH LATTICE INSTABILITIES" M. Núñez Regueiro. Solid State Communications 60, 797 (1986). "A DIMENSIONAL KRONIG - PENNEY MODEL" A.R. Goñi, A.G. Rojo, E. N. Martinez. American Journal of Physics 54, 1018 (1986). "SPECIFIC HEAT OF 1^ eSrQ 2Cu04: ANOMALY AT THE SUPERCONDUCTING TRANSITION" G.I.. Nieva, E. N. Martínez, F. de la Cruz, D. Esparza, C. D'Ovidio. Physical Review B36, 8780 (1987). "SPECIFIC HEAT MEASUREMENTS IN SCANDIUM - RARE EARTH ANISOTROPIC SPIN GLASSES" P. Pureur, G. L. Fraga, D.E. Brandao, R. Caudron, H. Safar, G. L. Nieva. J. of Magnetism and Magnetic Materials 68, 213 (1987). "B OF HIGH-T La Sr CuO AND AMORPHOUS Zr Cu SUPERCONDUCTORS MEASURED BY A VIBRATING REED" C. Duran, P. Esquinazi, J. Luzuriaga, E.H. Brandt. Physics Letters A123, 485 (1987). "ANOMALOUS BEHAVIOR OF SUPERCONDUCTING SAMPLES WITH A FIXED NUMBER OF VORTICES" L. Civale, F. de la Cruz. Physical Review B36, 3b6O (1987). "CURRENT VOLTAGE CHARACTERISTICS IN COLLECTIVE PINNING" F. de la Cruz, .]. Luzuriaga, E. N. Martinez, E.J. Osquiguil. Physical Review B 36, 6580 (1987). "ANOMALIES IN THE INTERNAL FRICTION AND SOUND VELOCITY OF La Sr Cu " 1.8 0.2 4 P. Esquinazi, J. Luzuriaga, C. Duran, D. Esparza, C. D'Ovidio. Physical Review B36, 2316 (1987). "CRITICAL BEHAVIOR OF YOUNG'S MODULUS FOR TWO-DIMENSIONAL RANDOMLY HOLED METALLIZED MYLAR" J. Sofo, .1. Lor-enzana, E. N. Martinez. Physical Review B36, 3960 (1987). "PINNING FORCES AND DEFECTS AS MEASURED BY CRITICAL CURRENTS IN AMORPHOUS SUPERCONDUCTING MATERIALS" J. Luzuriaga. Physical Review B3S, 3625 (1987). "THKRMA1. AND MAGNETIC ANOMALOUS CRYSTAL FIELD EFFECTS IN Ce-Hf COMPOUNDS" G.I.. Nieva, J.G. Serení, J. P. Kapplcr. Physica Soripta 35, 201 (1987). "PENETRATION DEPTH OF' A SUPERCONDUCTING SUPERLATTICE" .1. Cuimpel, F. de la Cruz, J. Murduck, I. K. Schuller. f'hysical KeviewBrW, 36.45 (1987). "THE GRANULAR NATURE OF BULK SUPERCONDUCTIVITY AT 40K IN La Sf C:uO " 1.8 O.'A 4 IJ. Esparza, C. IVOvidio, J. Gu impel, E.J. Osqulguil, L. Civale, I-', do la Cruz. Solid SI ato Communications ti3, 137 (1987). "CONNECTIVITY CONDITION AND REENTRANT PHASE TRANSITION IN Ba(PbBi)O CKANULAR SUPERCONI .UCTOR. ll.(¡. ¡¡t.einmnn, I'. "ANOMALOUS CRYSTAL FIELD EFFECTS IN THE SPECIFIC HEAT OF Ce-HEAVY l-ri'.MinN COMPOUNDS" ... I,. Servni , (;, I.. Nievü, J.P. Kappler. .! ul' MHLgnol.iiiin and Magnetic Materials 63/64, 101 (1987). "I:VIDF:NI:I-: OK ir-INSTABILITY OF DILUTE TERBIUM IN THORIUM" i.e.. Serení, r;. 1.. Nieva, J.G. Huber, E. Braun, F. Oster, E. Briick, it. Uodon, D. Wohl I obeli. .1. '-.f Mar/ioU-,m ¡m<1 Magnetic Materials 63/64. 597 (1987). 7-.fJOMAI.OUS TJIKIiMAI. COriDUCTIV1TY OF La Sr CuO : POSSIBILITY OF A 2-x x 4 rol.AHONIC (;LASS" M. Núíic/. r "KVinENCK OF LOW ENERGY TUNNELING EXCITATIONS IN THE HIGH T c K'Jl>KKi:ONl;UCTOn.S YBa Cu 0 " ?. 3 7-x P. Esquina/.i, C. Duran, C. Fainstein, M. Nunez Regueiro. rhyrjical Review B (to be published). "VIBRATING REED STUDIES OF FLUX PINNING IN ZrCu METALLIC GLASS" iJ. Esqui nazi, .1. Luzuriaga, C. Duran. Physical Review 1! (to bo published). "ANOMALIES IN THE INTERNAL FRICTION AND SOUND VELOCITY IN YBa Cu O 2 3 7-x AND Eulia Cu O SUPERCONDUCTORS" V. :i 7-x ('. luirán, IJ. Eaquinazi, C. Fainstoin, M. Núñe?. Regueiro. Soiid State Communications (to be published). - 47 '/' "CRYSTAL FIELD INTERACTION IN THE Gd Eu BaCuO . SUPERCONDUCTORS" X l-x 2 3 7-O M. T. Causa, C. Fainstein, G. Nieva, R. Sánchez, L. B. Steren, M. Tovar, R. Zysler, D.C. Vier, S. Schultz, S. B. Oseroff, Z. Fisk, J. L. Smith. Physical Review B (to be published) "UNEXPECTED MAGNETID BEHAVIOR IN A SINGLET CRYSTAL FIELD GROUND STATE INDUCED BY Tb-4f INSTABILITIES" E. Braun, A. Bürger, G. L. Nieva, B. Roden, J.G. Sereni. Z. fur Physik B (to be published). "ANNEALING EFFECTS ON THE SOUND VELOCITY AND INTERNAL FRICTION IN THE SUPERCONDUCTING AND NORMAL STATE OF Cu Zr AMORPHOUS ALLOY" 30 70 P. Esquinazi, J. Luzuriaga. Physical Review B (to be published). "THE NATURE OF THE MAGNETIC FLUX BEHAVIOR OF THE SUPERCONDCUTOR LaSr-CuO" L. Civale, H. Safar, F. de la Cruz, D. Esparza, C. D'Ovidio. Solid State Communications (to be published). -15o MAGNETIC RESONANCE I. STAKK Scientists Technician M. T. Causa J. C. Here/. S. M. Dutrúñ ° C. I'alnstein C. A. Ramos IB Graduate II. R. S.iLva * Students K. I). Sanchez + L. i!. Steren ++ A. Falnstein M. Tnvar * M. Servin R. I). Zysler + N. Vegllo CNKA/CON1CKT Id' + CNKA I'el low *"* CON1CKT Kellow Under contract C;I-:NI::HAL DKBCRIPTION The main interest of this group is the study of the magnetic properties of solids. Present research covers measurements of magnetization and magnetic resonance in compounds exhibiting different magnetic behavior: paramagnetic ions diluted in solids, spin-glasses and antiferromagnets. 2.1 Facilities: - Magnetic Resonance Spectrometer (ESR) operating at 9.5GHz and at 35GHz in the range between 1.5K and room temperature. Double Nuclear and Electronic Resonance Spectrometer (ENDOR) oper-at ing at .'iliOllz and radio-frequencies from 10M11/ to 80MHz. - Faraday magnetometer, operating in magnetic fields up to 1.3T and l.i;mpnr-aturo:; from 1. í¡K to TiOOK. - Resistivity bridge wit.h cryostat working between 55K and 300K. - Limited facilities for preparation of samples and their- thermal and mechanical treatment. Atomic absorption spectrometer Perkin Klmer 'A'.m li. 'Á.7. Cooperal. i on Anreements: The group corviuci.fi re«;earch programs in cooperation with the Col lowing l.'iboi'iil.or'iff;: - Magnetic Resonance Laboratory, Physics Department, University of California, San Diego, U.S.A.. - Laboratorio de Resonancias Magnéticas, INTEC, CONICET, Santa Fé, Argent i na. - Laboratorio de Resonancias Magnéticas, Centro de Fisica, Instituto Venezolano de Investigaciones Científicas (IVIC), Caracas, Venezuela. - laboratorio de Espectroscopia Mossbauer, Depto. de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina. - Centre des Kecherirhcs sur les Tres Basses Temperatures, CNRS, Grf'noblc;, I r;inci>. Institute do Physique Applique, Ecole Polytechnique Fedérale, Lausanne, Switzerland. 2. 3 Conferences: The íotaí'f of the Division have participated in several International Conferences - IX ISMAR MEETING, Rio de Janeiro, Brazil, June 29 - July 5, 1986. XXI I I AMPKRK CONGRESS, Roma, Italy, September, 1986. - 53 - ADRIÁTICO RESEARCH CONFERENCE ON HIGH TEMPERATURE SUPERCONDUCTORS, ICTP, Trieste, Italy, 5-8 July, 1987. SECOND EUROPEAN WORKSHOP ON CHARGE DENSITY WAVES, Aussois, France, September, 1987. II SEMINARIO LATINOAMERICANO DK ANÁLISIS POR TÉCNICAS DE RAYOS-X, Bahía Blanca, Argentina, 9-14 November, 1987. 32nd ANNUAL CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS, Chicago, U.S.A. , November, 1987. - 54 - 3. RESEARCH PROGRAMS A. Properties of Paramagnetic ions in Solid Solution: EPR (Electron paramagnetic resonance) and ENDOR (Electron nuclear double resonance) techniques are used to study the interaction of isolated magnetic ions with neighboring atoms of the matrix. Phenomenological models for the stress dependence are used to analyze the data and determine values for the crystal field parameters ;ind hyper fine structure constants as functions of temperature and applied uniaxial stress. Comparisons are made with microscopic models of the interaction between the electrons and the nuclei of neighboring atoms, taking into account the effect of local distortions of the lattice at the impurity site. 13. Spin Glasses: Work in this area, is oriented towards a characterization of their magnetic behavior especially in so called metallic spin glasses, in which the dominant, mechanism is the interaction of localized magnetic moments via conduction electrons. The magnetic anisotropy of the system as a function of temperature and previous history of the samples wa:> determined through magnetic resonance and magnetization measurements. This is a joint project with physicists at. the University of California, San Diego, U.S.A. (NSF-CONICET joint cooperation agreement). - 55 - C. Antlferromagnets: Insulators showing a paramagnetic-to-antiferromagnetic transition as a function of temperature are characterized through ant iferromagnetic resonance spectroscopy (AFMR). Measurements at different temperatures as a function of frequency allow us to analyze the role of the interaction mechanisms: exchange, dipole-dipole interactions, crystal field and spin lattice relaxation. D. Electric transport properties in One-Dimensional Solids: The non-linear behavior of the electric current and electric field has been studied in compounds such as TaS and (TaSe ) I, which 3 4 2 have a metallic chain structure. The analysis of the behavior of resistivity with applied field has led to the observation of new effects in the response of such samples to current pulses. Further work is in progress. There are current cooperation agreements with CRTBT, Grenoble, France and IPA-EPFL, Lausanne, Switzerland. E. High T Superconducting Ceramics: Work in this area began in February"87 with the preparation of Y-Ba-Cu-0 type ceramics (T > 90K). Research focussed originally on: I - Effect of the substitution of 3d (Fe, Mn) for the Cu atoms on the - 56 - compound's superconducting properties. II - Effects due to the substitution of 4f rare earth ions (Eu, Gd, Dm, Er, Dy) for the Y atoms. We have verified that there is no change in the superconducting properties. However, magnetic ordering was observed in some compounds (Gd, Er, Dy). Particular attention was given to: 1) A Ba2Cu307+g (A = Y, Gd, Eu, Sm, Er, Dy) 2) Y Ba [Cu Fe ] 0 _ ( 0 < x < 0.10) 1 2 l-x x 3 7-6 3) (Eu Gd ) BaCuO . (0 < x < 1) l-x x ) 2 3 7-5 Structural and magnetic properties of these compounds were studied through powder x-ray diffraction, electrical resistivity vs. temperature, magnetic susceptibility as function of magnetic field and temperature, EPR, Mossbauer spectroscopy and specific heat as a function of temperature. - 57 - 4. CONFERENCES AND PUBLICATIONS 4.1. CONFERENCES 4.1.1. International Conferences - IX ISMAR MEETING, Rio Ue. Janeiro, Brazil, June 2S - July 5, 1986: "Transfered Hyperfint: Interaction of 4Í"1 Rare-Earth Impurities in Fluori tes" C. Fainstein, C. A. Ramos, M. Tovar. - XXIII AMPERE CONGRESS, Rome, Italy, September, 1986: "Stress Induced Electronic g-shifts for 4f Ions In Fluoriies" C.A. Ramos, M. Tovar, C. Fainstein. - ADRIÁTICO RESEARCH CONFERENCE ON HIGH TEMPERATURE SUPERCONDUCTORS, ICTP, Trieste, Italy, 5th - 8th July, 1987: "Magnetic and Structural Properties of Some ABa Cu O Superconductors" M.T. Causa, S.M. Dutrus, C. Fainstein, G. Nieva, H.R. Salva, • •:. Sánchez, L.B. Steren, M. Tovar, R. Zysler. - SECOND EUROPEAN WORKSHOP ON CHARGE DENSITY WAVES, Aussois, France, September, 1987: "New Effects in the Nonlinear Regime of Monoclinic TsS " H. Salva, M. Servin, P. Monceau, F. Levy, A. Meerschaut. - 32nd ANNUAL CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS, Chicago, U.S.A. , November 1987: "Stabilization of the Tetragonal Phase of YBa Cu O through the 2 3 7—5 Addition of Fe Impurities" M.T. Causa, S.M. Dutrus, C. Fainstein, H.R. Salva, L.B. Steren, M. Tovar, R. Zysler. - II SEMINARIO LATINOAMERICANO DE ANÁLISIS POR TÉCNICAS DE RAYOS-X, Bahía Blanca, Argentina, 9-14 September, 1987: "Preparación de Cerámicos Superconductores de Alta Temperatura; Caracterización Mediante Difractometría de Rayos-x" M.T. Causa, S.M. Dutrús, C. Fainstein, H.R. Salva, R. Sánchez, L.B. Steren, M. Tovar, N. Veglio, R. Zysler. - 58 - 4.1.2. Domestic Conferences 71a REUNION DE LA AFA, Córdoba, October, 1986: "Obtención de Trisulfuro de Tantalio por el Método de Transporte Gaseoso" M. Servin, H. Salva. "Magnetización y Resonancia Magnética de Cu(L - leu)2. Dependencia en Temperatura entre 1.5K y 300K" A. Fainstein. R. Zysler, G. L. Nieva, C. Fainstein, M. Tovar, C.A. Steren, R. Calvo. "K:;tudio de Propiedades Magnéticas del FeNaP 0 " M. Prado, R. Zysler, C. Fainstein, M. Tovar, L. Terrainiello, L. A. Mendoza Zélls, A.R. López García, R.C. Mercader. "Características del Magnetómetro de Faraday Construido en el CAB" M. Prado, R. Zysler, C. Fainstein, J.G. Sereni, M. Tovar. - 1?.:\ REUNION DE LA AFA, Bariloche, September 1987: "estabilización de la Fase Tetragonal de YBa Cu 0 a través de la 2 3 7 Incorporación de Impurezas de Fe" M. T. Causa, S. M. Dutrús, C. Fainstein, H. R. Salva, L.B. Steren, M. Tovar, R. Zysler. "Interacción del Campo Cristalino y Orden Magnético en (RE) Ba Cu 0 " 2 3 V M. T. Causa, S. M. Dutrús, C. Fainstein, G. L. Nieva, H. R. Salva, K. Sánchez, L.B. Steren, M. Tovar, R. Zysler, S. B. Oseroff, J.L. Smith. "Crecimiento de Monocristales de Cerámicos Superconductores" S.M. Dutrús, M. T. Malachevsky, D. Esparza, H. Salva. "Propiedades Normales de Algunos Superconductores Magnéticos de Alta Tc: (RE) BaaCu307" M. T. Causa, S.M. Dutrús, C. Fainstein, H. R. Salva, L.B. Steren, M. Tovar, R. Zysler. "Efectos Anómalos en el Estado Nolineal en TaS3 Monoclínico" H. Salva, M. Servin, P. Monceau, F. Levy, A. Meerschaut. 4.4 Publications: "TRANSFERED HYPERFINE INTERACTION IN THE ESR SPECTRA OF Eu2+ IN CdTe" M. Tovar, M.T. Causa, S.Ü. Cfeeroff. Physical Review B36., •''•"- 03?). "MAGNETIC AND STRUC- iAL PROPERTIES OF SOME ABa Cu O 2 3 7-5 SUPERCONDUCTORS" M.T. Causa, S. M. Dulrus. C. Kains>.t:in, G.L. Nieva, H. R. Salva, R. Sánchez, L.B. Steren, M Tovsr, P.. Zysler. Int. Journal of Modern Physics Bl_, 909 (1987). "EVIDENCE OF LOW ENERGY TUNNELING EXCITATIONS IN THE HIGH T c SUPERCONDUCTORS YBa Cu O •• 2 3 7-x P. Esqulnazi, C. Duran, C. Fainstein, M. Núñez Regueiro. Physical Review B (to be published). "ANOMALIES IN THE INTERNAL FRICTION AND SOUND VELOCITY IN YBa Cu O 2 3 7-x AND EuBa Cu O SUPERCONDUCTORS" 2 3 7-x C. Duran, P. Esquinazi, C. Fainstein, M. Núñez Regueiro. Solid State Communications (to be published). "STABILIZATION OF THE TETRAGONAL PHASE OF YBaaCu307_6 THROUGH THE ADDITION OF Fe IMPURITIES" M.T. Causa, S.M. Dutrus, C. Fainstein, H. R. Salva, L.B. Steren, M. Tovar, R. Zysler. Applied Physics Letters (to be published). "OXYGEN ENVIRONMENT OF Fe IONS IN YBa Cu O : A MÜSSBAUER STUDY" C. Saragovi-Badler, F. Labenski-Kanter, M.T. Causa, S.M. Dutrús, C. Fainstein, L.B. Steren, M. Tovar, R. Zysler. Solid State Communications (to be published). "CRYSTAL FIELD INTERACTION IN THE Gd Eu Ba Cu O . SUPERCONDUCTORS" X l-x 2 3 7-6 M.T. Causa, C. Fainstein, G.L. Nieva, R. Sánchez, L.B. Steren, M. Tovar, R. Zysler, D.C. Vier, S. Schultz, S. B. Oseroff, Z. Fisk, J.L. Smith. Physical Review B (to be published). - 61 - METAL PHYSICS I. STAFF Scientists Technicians A. Abu Arab ++ A. C. Vecchiet M. Ahlers C. Gomez E. Bisogni A. Cuniberti ** F. C. Lovey J. Pelegrina ++ R. Rapacioli * J. Regolini *° IB Graduate E. Romero *** Students M. Sade A. Salva P. Decorte A. Tolley ** F. A. Saule CNEA/CONICET Researcher + CNEA Fellow CONICET Fellow Argentine Army UNCPBA Fellow On leave of absence in France - 63 - ?.. GENERAL DESCRIPTION The Metal Physics Division of the CAB is one of the oldest in the institution. The growth of the laboratory is due to the efforts of many Argentine and foreign scientists, many of whom are still connected with it. What is today the Applied Physics Department (from which sprang INVAP S. E. , the first high technology industrial enterprise in Argentina) originated in this Division. Many of its scientists are now continuing with their work in other official or private inst¡Lutions, thus creating a valuable two-way flow of knowledge. 2.1 Fácil i tics: a. Metallographlc Laboratory The group has the necessary equipment for surface treatment of metal specimens and for observation by optical microscopy. There are several metallographic microscopes and also accessories for applying tensile loads during observation and for varying tho temperature between 77K and 973K. b. Electron Microscopy Laboratory There is a Philips 300 transmission electron microscope with which areas with a maximum thickness of 0.3 microns can be studied, with a resolution of 1.2nm. Specimen holders for deformation, heating, cooling and rotation are available. - M - c. Internal Friction Laboratory There are three automated pendulums that operate in the 77K to 623K. range, with measurable deformation amplitude of 10"7 to 10~3. One of these pendulums has a window for electron irradiation. Oscillation frequencies are in the range of 1 to 5 Hz and 20 to 80 Hz, depending on the pendulum. There is also another pendulum for plastic deformation and cooling down to 4K. Finally, there is a system to excite vibrations in fiat specimens from 30 to 50 Hz, automated for a constant amplitude of lü"7 to 10"S, which functions from 77K up to 550K. d. Other equipment - Deforming machine: An ]n:.,':nn 1123 for applying loads of up to 2,!i00 kg with adjustable cross head velocities between 0.05 and iiOO /min. It. makes it possible to program experiments and has accessories for operating in different temperature ranges from 300K lo ÍS88K, from room temperature to 1473K (in a vacuum or in a controlled atmosphere) and from 77K to room temperature. - Dilatometer: The laboratory has a high speed quenching dilatometer LK02 for programmable; thermal treatments. The equipment has a range Al of K = 200, 400, 1000, 2000, 10000, and 20000, where K = is the Al m ratio between the Jen¿»th changes Al recorded on the chart and those of tho specimen it.s» to room temperature or from room temperature to 1473K; 1623K can be reached, but only In fast cycle. - Resistive and inductive furnaces for thermal treatments, alloy preparation and single crystal growth. - X-ray equipment including standard facilities. - Automated equipment, for coupled measurement of calorimetry and acoustic emission. - Cryostat: The construction of a cryostat which will operate at liquid He temperatures has recently been completed and will be installed and tested in the semiconductor laboratory (LASEM). e. Development of New K.ici 1 ities: As part of the Argentine-Spanish cooperation agreement on Thermoplastic Transformations, an automated facility for detecting (simultaneously), acoustic emission and heat evolution taking place during transformation has been designed, installed and perfected 'n cooperation with Spanish scientists from the Universities of Barcelona and Palma de Mallorca. 2.2. Cooperation Agreements: The Laboratory has cooperation programs with foreign and local research groups. These are: - 66 - Foreign institutions: - INSA, Lyon, France. - Université Catholique de Louvain, Belgium. - Universidades de Barcelona y Palma de Mallorca, Spain, Argentine Institutions: - FAMAF, Universidad de Córdoba: Study of precipitation in aluminium base alloys. - Dirección de Agua Pesada: Fragi1ization Project of Stainless Steel 304 L with Hydrogen (CNEA). - Universidad de Ciencias Exactas e Ingeniería, Universidad Nacional de Rosario. - Instituto de Física de Rosario, (IFIR) CONICET - Universidad Nacional de Rosarlo. - Instituto para el Desarrollo Tecnológico de la Industria Química, (INTEC) Santa Fé. - Universidad Nacional del Centro, Tandil. - 67 - 3. RESEARCH PROGRAMS A considerable part of the research activities is devoted to the study of the martensitic transformation in Cu-Zn based alloys. The study of martensitic transformations in the brasses is of particular interest not only because of the shape memory and double memory effects associated with them, but also because they serve as models for more comple-; materials, and because they show phenomena which are also of general interest in the field of metallurgy and the physics of mr.-tals. Cu-Zn and Cu-Zn-Al alloys are particularly well suited for si. ".dying the thermodynamics, crystallography and kinetics of the mart.on:;i t ic transformation, due to the small hysteresis between the direct and the inverse processes. These transformations make it possible t.o study the influence of thermomechanical treatments on the proper tie:; of both phases. An excellent technique for measuring anelastic effects is internal friction. This technique allows the study of configuration concentration and mobility ex defects, both interstitial and subst i tut ional, as well as the analysis of dislocations and interphasos. Research work on internal friction h;is been going on for many years now. A. Martensitic Transformati on: 1) PHASE STABILITY IN Cu-Zn AND Cu-Zn-Al ALLOYS The analysis of experimental information on enthalpy and entropy of the matrix and some martensit.ic phases shows that the - 68 - configurational entropy plays an important role on the relative phase stability due to the interaction between pairs of atoms, the vibrational entropy and the interaction between the Brillouin zone and the Fermi surface. Results obtained for stress induced martensitic transformation indicate that the role played by distortion energy due t.o the different sizes of the alloy atoms is less important. Energy measurements between orthorhombic and hexagonal martensite are scarce due to competitive transformations to other variants or phases which also take place. It was possible to induce an hexagonal phase in alloys with n/c (electronic concentration) > 1.5, in order to analyse ¡ Is .stab) ] i ty. X) MARTENSITIC TRANSFORMATION AND FERROMAGNETISM Studies on the iit'i-tonfjitic transformation in Cu-Mn-Al alloys have begun. These alloys also show a ferromagnetic effect. Changes in the magnetic proper!, ios have been .m.ilysod. Both phases present in the studied alloys due to the martensitic transformation were paramagnetic and changes in the susceptibility have been detected. 3) PLASTIC DEFORMATION IN THE MARTENSITIC PHASE On stressing a single martensitic crystal under either tension or compression, both plastic deformation and martensite-martensi te transformations can occur. Work has been carried out to analyse which t is dominant. - M - 4) FATIGUE Fatigue of single crystals due to the martensitic transformation depends on the experimental temperature and type of mechanical stress. Dislocations are created in the interior, martensite is retained and different kinds of defects are found at the surface where microcracks are originated. 5) STABILIZATION OF THE MARTENSITE IN Cu-Zn-Al ALLOYS If quenched martensite is obtained, its properties change due to the movement of retained vacancies which decreases the configurational, electronic and distortional free energy. The results obtained so far indicate that during stabilization a new long range order is created. This hypothesis makes quantitative evolution of the observation;; possible. 6) TRANSFORMATION INDUCED PLASTICITY Both the martensitic transformation and the plastic deformation of tt.e matrix produce a shape change of the crystal. Which effect predominates depends on the composition temperature range, and single crystal axis. Only in a small range are both effects competitive. The interaction between both deformation mechanisms ha:; been analysed. The movement of dislocations in the p phase and the induced transformation under high mechanical stresses have been studied. 7) MARTENSITIC TRANSFORMATION IN IRRADIATED Cu-Zn-Al By irradiation with neutrons and electrons vacancies are - 70 - produced, causing a change in the long range order. Therefore, the martensitic transformation should be affected. This effect is unstable when the martensite is irradiated with neutrons. The irradiation of the martensite affects the damping properties of mechanical vibrations. With the appropriate dosage these can be increased and, after a long time of room temperature aging, kept constant. Friction peaks at 20 Hz as a function of time are studied both during the transformation and in a range of the martensite phase. B. Interna] Friction: 1) MICROSCOPIC AND ANKLASTIC STUDIES IN ALUMINIUM BASED ALLOYS In commercial alloys, Al 2024, it is found that the hardening mechanism in dislocation brfik inp by metastable precipitates. Their instability is detected also when they are submitted to low doses of noutronic ami/or electronic irradiation. In commercial Al tiO63, we have continued the analysis of internal friction peaks due to precipitates and grain boundaries using t.herino-mechani cal tests. Anelastic parameters are taken into account. In commercial Ai 3001, studies have been made under the same rolling conditions as in industrial processes. The internal friction niousjurementñ make possible an explanation for the "plateau" in the l>lo(. of yield strerif't.n vf;rr;ur; previous plastic c jformat ion, as a saturation mechanism ir. the dislocation-precipitate interaction. - 71 -hi 2) FRAGILIZATION BY HYDROGEN IN STAINLESS STEEL This subject has not been continued during 1986/87 due to the time required for the elaboration of new samples. Pure Fe-Ci—Ni alloys will be studied by different metallurgical techniques, in collaboration with CNEA-CAC researchers. 3) GAS DETECTION IN METALS The Snoek peak in bcc metals, in particular for oxygen and nitrogen in the fi phase of Zr-Nb-Al alloys is being studied. The result is the following: The internal friction maximum shifts to the left in temperature around 100 C for 216 additional ppm of oxygen and :;hi I'tn to the right 10 0 for- 100 additional ppm of nitrogen. A new application of the Snoek effect in determining the nitrogen content in solid solution in ferritic steels obtained by welding is being explored. 4. CONFERENCES AND PUBLICATIONS 4.1. Conferences 4.1.1. International O.if ere ¡ices: - INTERNATIONAL CONFERE.;: .• ,.'.'J MARTENSIT1C TRANSFORMATIONS, Tokyo, Japan, 1986: "Modulated Microstrc.:: i." os in Cn-2n-Al and the Premartensitic Phenomenon" G. van Tendeloo, M. Chandrasttkaran, F.C. l.ovey. "High Resolution Electron Microscopy of Defects and Twin Interfaces in 9H and 18R Martensites" F.C. Lovey, G. van Tendeloo, S. Amelinckx. "The Interpretation of Extra Spots in Electron Diffracion from 18R Martensite of Cu-Zn-Al" J.L. Pelegrina, M. Chandrasekaran, M.S. Andrade. "An Acoustic Emission and Calorimetric Study of Martensitic Transformation in Cu-Zn-Al" .:. Rapacioli, G. Guenin, J.L. Macqueron. "Fatigue in Cu-Zn-Al Single Crystals Stressed in Compression" M. Sade, F.C. Lovey, M. Ahlers. "The Stabilization of Martensite in Cu-Zn-Al Alloys" M. Ahlers. - PRIMER SIMPOSIO FRANCO-ARGENTINO DE CIENCIAS DE MATERIALES, Mar del Plata, Argentina, October 1986: 'Sobre la Naturaleza ae las Dislocaciones en Cu-Zn-Al Generadas por Deformación Plástica y Transformación Martensítlca Pseudoelástica" R. Romero, S. A. Uribarri, M. Sade, F.C. Lovey. - SOCIEDAD ALEMANA DE METALURGIA, GSttingen, Federal Republic of Germany, 1986: "Fatiga y Transformación Martensítica en Monocristales de Cu-Zn-Al" M. Ahlers, M. Sade, S. A. Uribarri, F.C. Lovey. "Sobre la Estabilidad de Fases Martensíticas en Aleaciones de Latones" M. Ahlers, R. Romero, A. Tolley. "La Estabilización de Martensita en Monocristales de Cu-Zn-Al por Envejecimiento" M. Ahlers, A. Abu Arab, M. Chandrasekaran. - 74 - INTERNATIONAL CONFERENCE ON CALCULATIONS OF PHASE DIAGRAMS (CALPHAD XV), London, England, 1986: "The Stability of MarteAsite Phases in Cu-Al and Cu-Zn-Al alloys" M. Ahlers. INTERNATIONAL CONFERENCE ON PHASE TRANSFORMATIONS, Cambridge, England, "Effects oí' Cycling through the Stress Induced Martensitic Transformation in Cu-Zn-Al Alloys on Dislocation Structures and Two Way Memory" M. Sade, A. flazarabodian, S. A. Uribarri, F.C. Lovey. "Decomposition and Precipitation in Al-Hn-Ag Alloys" A. Ghilarducci, J.P. Simon, M. Audier. EUROPEAN CONFERENCE ON INTERNAL FRICTION AND ULTRASONIC ATTENUATION IN SHEins, Belgium, 1987: "Detection of Oxygen Content in a Beta-Zirconium Based Alloy by Internal Friction" II. A. Porottl, A. Ghilarducci de Salva. "Internal Friction Peaks in a Commercial Duralloy" M. T. Malachevsky, A. Ghilarducci de Salva. "A Ni;w Relaxation Peak in a Solution Treated, Quenched and Annealed Al-Mg-Si Alloy" S. Urreta de Pereyra, h. Bertorello, A. Ghilarducci de Salva. 4.1.2. Domestic Conferences: Yla REUNION DE LA AFA, Córdoba,October, 1986: "Sistemas de Deslizamiento y Comportamiento Plástico de Latones (Cu-An-Al)" F.C. Lovey, R. Romero. "Estabilización de la Martensit.a Inducida en Cu-Zn-Al" A. Abu Arab, M. Chandrasekaran, M. Ahlers. "Efectos Anelásticos a Baja Frecuencia en Aluminio Comercial 2024" M.T. Malachevsky, A. Ghilarducci de Salva. SOCIEDAD ARGENTINA DE METALES, Buenos Aires, 1987: "Efectos Anelásticos y Microestructurales en una Aleación de Al-Mg-Mn Comercial Sometida a Tasas Graduales de Laminación" A. Ghilarducci de Salva. "Efecto Doble Memoria en Aleaciones de Cu-Zn-Al" A. Hazarabedian, M. Sade, F.C. Lovey. "Aplicación del Método de Rastegaev en el Análisis de la Transformación Martensícica Inducida por Compresión" H. Romero, J.L. Pelegrina. 72a REUNION DE LA AFA, Sari loche, September, 1987: "Tres Efectos de Relajación Interesante en Aluminio 6163" A. Ghílarducci de Salva ~ >'r •>••£?> de Pereyra, H. Bertorelio. "Defectos en Estructur '•'. ...iBuiw. .¡áenada" A. Tolley, F. C. Lovey, 0. fiios Jara. "Estabilización de Ir h.. i er.sita en Cu-Zn-Al" A. Abu Arab, M. Ahler - XV REUNION DE LA A. A. !". ;V\ . ¡iari :och<--. November, 1987: "Parámetros a Controlar para Mueve- '.teo d.e la Aleación Al-Mg-Si" S.E. Urreta de Pereyra, H. Betort.lo, A. Ghilarducci. 4.1.3. Invited Communications: CONFERENCIA INTERNACIONAL SOBRE TRANSFORMACIONES MARTENSITICAS, Nara, Japan, 26 -30 August, 1986: "The Stabilization of Martensite In Cu-Zn-Al Alloys" M. Ahlers. .'-MoSIMPOSIO NACIONAL DE ESTADO SOLIDO, Cuernavaca, Mexico, tí - 8 October, 1987: "Transformaciones Martensiticas" M. Ahlers - UNIVERSIDAD CATÓLICA DE LEUVEN, Belgium, June, 198B: "The Martensitic Transformation: A Solid State Phase Transformation" M. Ahlers. - UNIVERSIDAD DE MÜNSTER, Federal Republic of Germany, June, 1986 "The Martensitic Transformation" M. Ahlers. - INSTITUT NATIONAL DES SCIENCES APPLIQUÉES, Lyon, France, June, 1987: "High Resolution Electron Microscopy in Martensite" F.C. Lovey. - UNIVERSIDAD DE LAS ISLAS BALEARES, Palma de Mallorca, Spain, June, 1987: "Estabilización en Martens!ta Cu-Zn-Al" F.C. Lovey - 76 - .;...'.'..:,-.¿1 . !i." ANTWiaiPtN, Amberes, Belbium, 1987: "i-., I i»; . ...ur-L' ul1 l.he Mu.rtensi.tSc Transformation" r'.C. Lcvt.v. INST;'A;.''.J ¡I-: ÍNVESTÍCACIONFS EN MATERIALES, UNAM, Mexico, "Estabi J iiiad ^io Fases eri Metales y Aleaciones" M. Aüit-fs. - I'! 4.4. Publications: "HIGH TEMPERATURE TRAW : STABILIZED Cu-Zn-Al MARTENS1TE" M. Mantel, G. Guenin, .l.i.. Macqueron, J. Muntasell, R. Rapacioli, A. Planes. Scripta Metal lurgica ?'.. •¡•<3 (1986). "PHASE RELATIONSHIPS A-::; •..-ABILITIES OF THE a, THE |3 AND VARIOUS MARTENSITIC PHASES IN SxV-ScS" M. Ahlers. TMS Book Series - iJha.:i.- Tj¡a:,.-:iííis. Alloy Phase Stability and Thermodynamic Aspects oí ';i'...¡i> V-.a! Alloys", ed. T. B. Massalski, E. B. Pearson, L. H. Bennett, Y. A. unang. Metallurgical Society, 1986, pp. 87-108. "MARTENSITE AND EQUILIBRIUM PHASES IN Cu-Zn- AND Cu-Zn-Al ALLOYS" M. Ahlers Progress in Materials Science 30, N°3 (1986). "MODULATED MICROSTRUCTURE IN Cu-Zn-Al" G. van Tendeloo, M. Chandrasekaran, F.C. Lovey. Metallurgical Transactions AH, 2153 (1986). •r ATIGUE IN Cu-Zn-Al SINGLE CRYSTALS STRESSED IN COMPRESSION" M. Sade, F.C. Lovey, M. Ahlers. Proc. of the ICOMAT, The Japan Institute of Metals, Japan (1987) pp 934. "HIGH RESOLUTION ELECTRON MICROSCOPY OF DEFECTS AND TWIN INTERFACES IN 2H AND 18R MARTENSITES OF Cu-Al ALLOYS" F.C. Lovey, G. van Tendeloo, J. van Landuyt, S. Amelinckx. Proc. of the ICOMAT, The Japan Institute of Metals, Japan (1987) pp 762. "THE INTERPRETATION OF EXTRA SPOTS IN ELECTRON DIFFRACTION FROM 18R MARTENSITE OF Cu-Zn-Al" J. Pelegrina, M. Chandrasekaran, M.S. Andrade. Proc. of the ICOMAT, The Japan Institute of Metals, Japan (1987) pp 812. "MODULATED MICROSTRUCTURES IN /3Cu-Zn-Al AND THE PREMARTENSITIC PHENOMENON" G. van Tendeloo, M. Chandrasekaran, F.C. Lovey. Proc. of the ICOMAT, The Japan Institute of Metals, Japan (1987) pp 868. "AGEING OF QUENCHED Cu-Zn-Al ALLOYS IN BETA AND IN THE MARTENSITE STATE" M. Mantel, R. Rapacioli, G. Guenin. Proc. of the ICOMAT, The Japan Institute of Metals, Japan (1987) pp 880. "THE STABILIZATION OF MARTENSITE IN Cu-Zn-Al ALLOYS" M. Ahlers. Proc. of the ICOMAT, The Japan Institute of Metals, Japan (1987) pp 786. - 7ri - "THE FAULT DENSITY I,v 9R TYPE MARTENSITE. A COMPARi'SOx BETWEEN EXPERIMENTAL AND CALCULATED RESULTS" F.C. Lovey. Acta Metallurgica 35, '.103 (1987). "AN ELECTRON MICROSCOPY STUDY OF DISLOCATION STRUCTURES IN FATIGUED Cu-Zn-Al SHAPE MEMORY ALLOYS" M. Sade, S.A. Uribarri, F.C. Lovey. Philosophical Magazine A55, 447 (1987). "SYSTEMATIC STUDY OF MARTENSITIC TRANSFORMATION IN A Cu-?:i-Al ALLOY. OPTICAL MICROSCOPY AND SIMULTANEOUS THERMOSONIMETRY OF A MICROPLATE" C. Pi Cornell, C. Seguí, V. Torra, F.C. Lovey, R. Rapacioli. Thormochimica Acta 113, 171 (1987). "ACOUSTIC EMISSION DURING THE MARTENSITIC TRANSFORMATION OF SMALL MICROPLATES IN Cu-Zn-Al ALLOYS" t'.C. Lovey, J. Ortin, V. Torra. Physics Letters A21_, 3t>2 (1987). "ACOUSTIC EMISSION AND LOCAL CHANGES IN MARTENSITIC TRANSFORMATION" F.C. Lovey, E. Cesari, V. Torra, J. Guilemany. Materials Letters; H, 1bi9 (1987). "AN 1 SOTROPY OF CLUSTERING DURING DECOMPOSITION OF AlZn SINGLE CKYSTAI S" A. C.hi larducc) , J.P. S.inon, F. Livet, P. Guyot. Script.a Metallurgica 2\_, 1061 (1987). "MICH RESOLUTION ELECTRON MICROSCOPY IMAGING OF THE HABIT PLANE IN Oi-Zn-Al SHAPF. ALLOYS" !•'.<:. Lovey, G. van Tenc-eloo, J. van Landuyt. Scr-ipta MotallurRica 7¿_, 1626 (1987). "PHASE STABILITY AND TKE MARTENSITIC TRANSFORMATION IN Cu-Zn ALLOYS"R. hornero, M. Ahlers. .Journal of Physics F (v.o be published). "FORBIDDEN REFLECTIONS IN [100] ZONE ELECTRON DIFFRACTION PATTERNS FROM M18R Cu-Zn-Al MARVENSITE AND THEIR INTERPRETATION" J.L. Pelegrina, M. Char.drasekaran, M.S. Andrade. Acta Metallurgica (to be published). "PLASTICITY IN ft PHASE Cu-Zn-Al ALLOYS" R. Romero, F.C. Lovey, M. Ahlers. Philosophical Magazine (to be published). "THE STABILIZATION OF KARTENSITE IN Cu-Zn-Al ALLOYS" A. Abu Arab, M. Ahlers. Acta Metallurgica (to be published). NEUTKON AND REACTOR PHYSICS 1. STAFF Scientists Technicians M. J. Abbate * R. E. Bravo J. Oawldowskl ++ L. Capararo V. H. Gillette + J. R. Granada IB Graduate F. Kropff Students R. E. Mayer M. M. Sbaffoni P. C. 'lorido N. E. Patino CNEA Fellow CONICET Fellow Argentine Army - 81 - 2. GENERAL DESCRIPTION Research in this Laboratory involves experimental, theoretical and computational activities related to the interaction of neutrons with matter. Thermal neutron diffraction and transmission techniques are being employed, to study the structural properties of materials and to determine the nuclear constants which characterize the interactions of slow neutrons with nuclei. In the Neutron Physics area research is on the properties and characteristics of the neutron field in several systems of interest, including fuel cells in advanced reactors. Z. 1. Facilities: The experimental activity of the Laboratory is based on a pulsed neutron source, consisting of an electron beam accelerated (25 MeV) in a LINAC which hits a heavy target. The intensity of the fast neutrons 12 produced in each pulse is around 10 n/sec. Experiments are performed using the time of flight technique; at present the laboratory has a flight tube 70m long, with detection stations at 17m, 8m and 3m. This line is usually employed for neutron spectroscopy and total cross section measurements. There is also a 5m flight tube, at the end of which a time-focussed diffractometer has been mounted. The facility also includes a data acquisition system, which involves timing and pulse height analysis as well as the "on-line" data recording through a time encoder and a computer. A new acquisition system based on a single microcomputer is under - 82 - development. Other experiments use foil activation techniques, employing a Ge-(Li) detector for the corresponding measurements. Five personal computers which can also be connected to the VAX 11/780 system, are usea to process the data, carry out calculations and develop new computer programs. The Laboratory has a library of computer codes of more than 150 elements, most of them developed locally. 2.2. Cooperation Agreements: Several cooperation agreements have been entered into with other laboratories through various agencies such as NSF and the Argentine-German Cooperation Agreement. At present the following projects are under way: - "Neutronic Studies in Compact Lattices", with the support of the U.N. Development Program and of the IAEA. - "Neutron Coherent and Incoherent Cross Sections", in collaboration with the FRM Reaktorstation Garching der Technischen Universitát München, within the framework of the Argentine-German Cooperation Agreement. The laboratory is also connected with the following institutions: - Virginia Polytechnic Institute and S.U., Blacksburg, Virginia, USA. - KRM Reakt.orstalion Garching, Technischen Universitát München, West Germany. - 83 - - Kernforschungzentrum Karlsruhe, Karlsruhe, West Germany. - Technische Universitát zu Braunschweig, Braunschweig, West Germany. - Universitát Stuttgart, Stuttgart, West Germany. - Research Reactor Institute, Kyoto University, Japan. - Centro di Recerche Ezio Clemente I, ENEA, Bologna, Italy. - Schweizer Bundesinstitut fur Kernforschung, Wiirenlingen, Switzerland. 2.3. Conferences: Researchers of the Laboratory take part regularly in international conferences, either with invited talks, personal attendance or with contributed papers (see 4.1). - 84- RESEARCH PROGRAMS A. Neul.ron Interaction v;ith Condensed Matter: Neutron diffraction and transmission techniques are a valuable tool for condensed matter research, due to their ability to determine the structure and dynamics of a system through the measurement of elastic and inelastic cross sections. A pulsed neutron source permits a high momentum transfer to be attained in scattering experiments, thus allowing a large number of Bragg reflections to be observed in I.ho case of crystalline solids or well defined oscillations in the fase of liquids or amorphous systems. The experimental activity includes total and differential cross suction measurements, using the LINAC as a pulsed neutron source in combination with timc-of'-flight techniques. Diffraction experiments are carried out on sample;: within a wide range of temperatures, providing information on t he thermal displacements of the nuclei as well as on anharmonic motion in crystalline solids, phase transitions and the structure of solids and liquids. Transmission experiments are performed using neutrons with criprgie:; from ñubthermal up to opithermal values. These measurements, when combined with a precise calculation of the total cross section, provide a consistent set of values for the coherent and incoherent cross sections. These magnitudes characterize the slow neutron rwtclttua Interaction an¡l make possible the prediction of the total cross section of a given element at any temperature. During this period, total cross section measurements were carried - 85 - out on S, Bi, Ga and polyethylene, and neutron diffraction was used to study high critical temperature superconducting ceramics. A theoretical model has been developed to describe the interaction of thermal neutrons with molecular gases. The model has been applied to neutron thermal ization problems in moderators, with satisfactory results. At present inelasticity corrections required in structural studies on molecular systems are being evaluated with the use of the synthetic scattering function derived from the model. The analytical expressions derived from the model are being employed for the generation of (thermal) nuclear data in different systems and as a function of temperature. B. Neutron Hiysi es Studies on Nuclear Systems: To obtain data on neutron properties, and to understand neutron field behavior, neutron physics studies are carried out in different kinds of multiplying and non-multiplying assemblies, as well as in homogeneous or heterogeneous systems. The experimental techniques used,(which might globally fall under the label of "neutron spectroscopy techniques"), are those commonly employed for differencial and integral spectrum measurements: time-of-flight, foil activation, die-away, etc.. By such means, different kinds of neutron parameters can be obtained, e.g. neutron cross sections, neutron diffusion constants, multiplication factors, reaction rates, neutron energy spectra, etc.. Up till now we have studied thermal energies, however the -86 - possibilities of research in intermediate and fast energy ranges are currently being developed and new instrumentation has been purchased and put into operation. The new energy range is necessary for the experimental study of the compact fuel lattices which characterize high conversion reactors. As part of the U.N. Development Program and IAEA project "Neutronic Studies in Compact Lattices", a comprehensive bibliographic analysis was carried out on the state-of-the-art in high conversion ri;:ir:t.or research, Identifying open research and development problems. Necessary data sets were generated, and the first cell calculations were performed. Sets of neutron cross sections have also been tested and validated by comparison of the experimental results with numerical calculations, by means of different computational codes. From the theoretical point of view, various methods of solving the neutron transport equation are being studied, as well as the acceleration methods used by Sn codes. A new group-by-group method has been developed and implemented in DOT 3.5 - CAB code. - 87 - 4. CONFERENCES AND PUBLICATIONS 4.1. Conferences: 4.1.1. International Conferences - SEMINAR ON NUCLEAR DATA, JAERI, Tokai-Mura, Japan, November, 1986: "Thermal Neutron Cross Sections: Transmission Experiments and Model calculations" J.R. Granada (Invited Talk). 4.1.2. Domestic Conferences - 71a REUNION DE l.A AFA, Córdoba, October, 1986: "Sección Eficaz del Pol let i leño para Neutrones. Mediciones y Cálculos" J. Dawidowski, R. E. Mayer, J.R. Granada, V.H. Gillette. "Secciones Eficaces Totales de Azufre, Bismuto y Galio para Neutrones Térmico" .I.E. Mayer, V.H. Gillette, J.R. Granada. "Difracción de Neutrones por Tiempo de Vuelo" R.E. Mayer. - XIV REUNION DE LA A.A.T.N., Córdoba, October, 1986: "Estado del Arte en las Investigaciones sobre Reactores Avanzados" M. M. Sbaffoni, M. J. Abbate. "Problemas de Cálculo Neutrónico de Reactores Nucleares de Alta Conversión" M. J. Abbate, M. M. Sbaffoni. - 72a REUNION DE LA AFA, Bariloche, September, 1987: "Difraccción de Neutrones en La Sr CuO : Identificación 1.8S .15 4-y Estructural de Vacancias de Oxígeno" J.R. Granada, R.E. Mayer, V.H. Gillette, J. Dawidowski. 4.2. Invited Talks: - RESEARCH REACTOR INSTITUTE, REACTOR PHYSICS DIVISION, KYOTO UNIVERSITY, Japan, September, 1986: "Neutron Scattering Lengths" J.R. Granada. - RESEARCH REACTOR INSTITUTE, GENERAL SEMINAR, KYOTO UNIVERSITY, Japan, October, 1986: "Research Activities \n the Neutron Physics Division - CAB, Bariloche, Argentina" 88 - J.R. Granada. NUCLEAR ENGINEERING DIVISION, OSAKA UNVIERSITY, Japan, October, 1986: "Neutron Thermal ization in Moderators" J.R. Granada. RESEARCH REACTOR INSTITUTE, REACTOR PHYSICS DIVISION, KYOTO UNIVERSITY, Japan, Octooer, 1986: "A Synthetic Model for Neutron Thermalization" J. R. Granada. - 89 - 4.4. Publications: "INELASTICITY CORRECTIONS IN THERMAL NEUTRON SCATTERING BY MOLECULES USING A SYNTHETIC (INCOHERENT) SCATTERING FUNCTION" J.R. Granada, V.H. Gillette, R. E. Mayer. Physlca B142, 223 (1986). "NEUTRON DIFFUSION PARAMETERS OF H2O AND D20 AS A FUNCTION OF TEMPERATURE" J.R. Granada, V.H. Gillette, R. E. Mayer. J. Nuclear Materials 139, 158 (1986). "ON THE DESIGN OF TIME-FOCUSED DETECTOR BANKS FOR PULSED NEUTRON TOF SPECTROSCOPY" F. Kropff Nuclear Instruments and Methods A245, 125 (1986). "A GROUP BY GROUP UPSCATTERING SCALING METHOD" M. M. Sbaffoni, M. J. Abbate. Annals of Nuclear Energy 13, 101 (1986). "THERMAL NEUTRON CROSS SECTIONS: TRANSMISSION EXPERIMENTS AND MODEL CALCULATIONS" J.R. Granada. Proc. of the 1986 Seminar on Nuclear DAta, JAERI, Tokai-Mura, Japan, JAERI-M 87-025, INDC (JPN), 109/L pp 312 (1987). "NEUTRON CROSS SECTIONS AND THERMALIZATION PARAMETERS USING A SYNTHETIC SCATTERING FUNCTION. II: APPLICATIONS TO H20, D20 AND C6H6" J.R. Granada, V.H. Gillette, R. E. Mayer. Physical Review A3J3, 5594 (1987). "TOTAL CROSS SECTION OF SULPHUR AT SLOW NEUTRON ENERGIES" R. E. Mayer, V.H. Gillette, J.R. Granada. Z. für Naturforschung A42, 791 (1987). "THERMAL NEUTRON CROSS SECTION AND TRANSPORT PROPERTIES OF POLYETHYLENE" J.R. Granada, J. Dawidowskl, R. E. Mayer, V.H. Gillette. Nuclear Instruments and Methods A2§!, 573 (1987). "ANNOYING TEXTURES, NEUTRON TIME OF FLIGHT AND MOVING SAMPLES" F. Kropff. J. of Physics E20, 1418 (1987). "EXPERIMENTAL NEUTRON DATA: SIGMA(E) OF SULPHUR AND BISMUTH IN THE THERMAL AND EPITHERMAL RANGE" R. E. Mayer, V.H. Gillette, J.R. Granada. Nuclear Data Section, IAEA, Expor Library (to be published). "EXPERIMENTAL NEUTRON DATA: SIGMA(E) OF POLYETHYLENE IN THE THERMAL RANGE" J. Dawidowski, J.R. Granada, R. E. Mayer, V.H. Gillette. Nuclear Data Section, IAEA, EXPOR Library (to be published). "EXPERIMENTAL NEUTRON DATA: SIGMA(E) OF Ga IN THE INTERMEDIATE ENERGY RANGE" R. E. Mayer, J.R. Granada, V.H. Gillette. Nuclear Data Section, IAEA, EXPOR Library (to be published). THEORETICAL PHYSICS COMPUTATIONAL PHYSICS 1. STAFF Scientists S. Bacci E. N. Miranda C. Moukarzei N. Parga + CNEA Fellow ++ CONICET Fellow - 93 - DESCRIPTION Interest in Computational Physics spurred the initiation of activities within the Theoretical Physics Division in the last two years. This is closely linked to the large recent advances in computer j design and architecture and the consequent generation of new and powerful techniques for solving problems in theoretical physics. 2.1 Facilities: In addition to full access to the main Computer Center in CAB through remote terminals the group is using a MicroVax II and peripherals (separate printing and graphics equipment). 2. ?. Joint Cooperation Agreements and Projects: These include: - One visit through the CONICET-CNRS (Argentine-French) agreement. - One associate at ICTP (Trieste, Italy). I - Contact through CLAF and TWAS with several Brazilian institut;ons interested in the design and construction of new computer architecture systems. - Particularly close contact with the University of Rome and the APE (array processor- with emulator) group. «• - Frequent and fruitful personal collaboration and contact with CERN (Geneve), Ecole Superiore de Paris, Universidad Católica de Chile and with scientists in Madrid and Marseilles. 2.3. Meetings in Bariloche: Th'> Arpas II meeting took place in February 1987 In CAB. Among those participating were the IFQSP and the University of Sao Paulo, from Brazil, the Escuela Latino Americana de Informática and several Argentine institutions: The Universities of Buenos Aires and La Plata and the TANDAR (with 15 participants). Talks at the meeting dealt extensively with computer architecture specifically designed for work in physics problems (both software and hardware). Several speciiic projects such as SIMD architecture (in t.h<; ARPAS project), and the design and construction of a machine for problems in molecular dynamics ire discussed in detail. :•'..'{. 1 ntornational Meetii.; - and s. to other Institutions: Scientists from this group participated in the following: - French-Argentine Theoretical Physics Colloquim (Buenos Aires, Argentina, 28th August - 5th September, 1986). - School on Statistical Mechanics (Sao Carlos, Brazil, January 1987). - III.AF (Latin American School of Physics) (La Plata, Argentina, July, 1987). - N. Parga (ICTP associate) stayed at ICTP in Trieste and afterwards visited: Ecole Nórmale Superieure de Paris and Universitá di Roma (Muy - July, 1987). lio also participated with lectures in the Workshop on the Theory of Disordered Systems in Biological Models (Bogota, Colombia, September, 1987) and in the Latin American - 95 - Meeting on High Energy Physics (Valparaiso, Chile, December, 1987). - 96 - :i. RESEARCH LINES A. Spin Glasses: An application was proposed of methods in biological taxonomy to study ultrametricity of mean field solutions for spin glasses at zero temperature. Results were compared with those of another model (ultrametric by original construction). These results have a general interest through their possible application to optimization problems, cellular automata and other systems. U. Problems in Combinatorial Optimization: The existence of ultrametricity among the quasi-opt imal configurations of the graph-colouring problem with q colors has been studied. This particular optimization problem was selected because perfect coloring is always possible when q£4. It was found that while for q = 3 the configurations show ultrametric organization this is not so for q = 4. The relation between ultrametricity and frustration is thus made evident: only when all constraints cannot be simultaneously satisfied do the quasi-optional configurations (obtained from minimization of a cost function), organize ultrametrically in configuration space. C. Noural Systems: Neural networks have been proposed as models for associative memory In the human brain. Each new memorized pattern is not required to be independent of those already learnt. A model has been studied - 97 - which makes it possible to store several interrelated memorized patterns. Uesults have been obtained for the total storage capacity as well as for the maximum possible number of uncorrelated stored patterns. D. Cellular Automata: Special attention has been given to Kaufman's model for cellular- automata, as its configuration space shares many charateristics with that of spin glasses. Several properties of the attractor cycles in Kaufman's model were investigated (ultrametriclty particularly). Also under study is the Q2R automaton, with which it is possible to make simulations of spin glasses of finite dimension and of Ising's model (microcanonical). ARPAS (Parallel Architecture) has as its immediate objective the design and construction of a machine for computational physics work. This project is being done in collaboration with the TANDAR laboratory and the Chemical Processing Management group. Training of all nccesKary human resources IK an integral part of this project. After a preliminary meeting (ARPAS II, Bariloche, Feb. 1987) in which a depth analysis was made of all aspects of this project, it was officially begun in August 1987. The system in designed to operate on SIMD architecture, with several calculating modules executing the same instruction with different data. This is particularly suitable for numerical - 98 - simulation of physical systems with local interaction as found in statistical mechanics, high energy physics and some image-processing algorithms. Hardware components include processing, memory and sequential operation units, the host interface and the interconnecting circuitry. Software includes the compiler and the control module. The Computational Physics group is working at present on the compiler, including language, microcode, and sequential unit minimal instruction package. This is being done in close contact with the engineering team in charge of the corresponding hardware elements. Two eLectronic engineers from CAB are also involved In the project. - 99 - 4. CONFERENCES AND PUBLICATIONS 4.1. Conferences: 4.1.1. International Conferences: - COMPUTACAO PARALELA APLICADA A PROBLEMAS DA FÍSICA TEÓRICA, COPPE/UFRJ, Rio de Janeiro, Brazil, 1986: "Requerimientos Computadonales de Algunos Problemas de Física Teórica" N. Parga. - COLOQUIO FRANCO-ARGENTINO DE FÍSICA, Buenos Aires, Argentina, September, 1986: "Simple Numerical Approach to Quantum Lattice Models" S. Bacci, E. Gagliano. "Overlap Distributions and Taxonomy Analysis of Spin Glass States with Equal Weights" N. Parga. - ESCUELA LATINOAMERICANA DE FÍSICA, La Plata, Argentina, July, 1987: "ültrametricidad y Coloreado de Gráficos" S. Bacci, N. Parga. "Autómatas Celulares y Vidrios de Spin" E. N. Miranda, N. Parga. 4.1.2. Domestic Conferences - 72a REUNION DE LA AFA, Bariloche, September, 1987: "Conceptos de Vidrios de Spin Aplicados a Autómatas Celulares" E. N. Miranda, N. Parga. 4.1.3. Invited Communications - V SIMPOSIO CHILENO DE FÍSICA, Santiago, Chile, December, 1986: "Modelos de Vidrios de Spin con Pesos Iguales. Análisis Taxonómico" N. Parga. - TALLER SOBRE TEORÍA DE SISTEMAS DESORDENADOS EN MODELOS BIOLÓGICOS, CIF, Bogotá, Colombia, September, 1987: "Ültrametricidad en Vidrios de Spin y Otros Sistemas Frustrados" N. Parga. - LATIN AMERICAN MEETING ON HIGH ENERGY PHYSICS, Universidad Federico - l.mi - Santa María, Valparaíso, Chiie, December, 1987: "Models of Associative Memories" N. Parga. Invi t.t; - PONTIFICIA UNIVERSIDADE CATÓLICA DE RIO DE JANEIRO, Brazil, 1986: "Vidrios de Spin y Modelos de Memorias Asociativas" N. Parga. - INSTITUTO DE FÍSICA Y QUÍMICA DE SAO CARLOS, USP, Brazil, 1986: "Modelos de Cerebro" N. Parga. - UNIVERSIDAD CATÓLICA DE CHILE, Santiago, Chile, December, 1986: "Aplicación de Mecánica Estadística a Modelos de Memorias Asociativas" N. Parga. - F.COi.K NÓRMALE SUPÉRIEURL, Paris, France, 1987: "The Kauffman Model and its Connection with the Sherrington-Kirkpatrick Model" N. Parga. - UNIVERSIDAD F. SANTA MARIA, Valparaiso, Chile, December, 1987: "On the Use of Spin Glasj Concepts in Optimization Problems" N. Parga (Talk given at ,'onferencia Latinoamericana de Física de Altas Energías, Valparaíso, Chile). - 101 -/ 4.4. Publications: "WARD IDENTITIES AND PHYSICAL INTERPRETATION OF ANOMALIES IN STOCHASTIC QUANTIZATION" M.B. Gavela, N. Parga. Physics Letters B174, 3:9 (1986). "WARD IDENTITIES AND CRiRAL ANOMALIES IN STOCHASTIC QUANTIZATION" M.B. Gavela, N. Parga. Nuclear Physics B275, 546 (1986). "THE ULTRAMETRIC ORGANIZATION OF MEMORIES IN A NEURAL NETWORK" N. Parga, M.A. VIrasoro. Journal de Physique 47, 1857 (1986). "OVERLAP DISTRIBUTION AND TAXONOMY ANALYSIS OF SPIN GLASS STATES WITH EQUAL WEIGHTS" N. Parga. Journal de Physique 48, 499 (1987). "A SIMPLE NUMERICAL APPROACH TO QUANTUM LATTICE MODELS" E. Gagliano, S. Bacci. Physical Review D36, 546 (1987). "ON THE USE OF SPIN GLASS CONCEPTS IN RA.JDOM AUTOMATA NETWORKS" E.N. Miranda, N. Parga. Europhysics Letters (to be published). "ULTRAMETRICITY OF THE KAUFFMAN MODEL: A NUMERICAL TEST" E. N. Miranda, N. Parga. Journal of Physics A (to be published). - 103 - THEORETICAL PHYSICS ELEMENTARY PARTICLES 1. STAFF Scientists IB Graduate Students M. L. Bruschi # M. Carena + I. Allekotte G. Demarco ++ C. Fosco A. García J. Russo L. Masperi F. D. Mazzitelli + R. Monteniayor ** R. Trinchero ** C. Wagner ++ ** CONICET Researcher + CNEA Fellow ++ CONICET Fellow ' IB - 105 - y.. GENERAL DESCRIPTION Research on Elementary Particles at CAB may be traced back to work directed by Francisco Morey Terry on dispersion relations in 19K3 and by Guido Beck on quantization of coupled fields in 1965. The group began its activity in 1968 with research on strong interaction phenomenology (Regge poles and dual models). In subsequent years the group made contributions to reggeon field theory. In the last five years the activity has been devoted to the study of phase transitions in spin and gauge models on the lattice, topological aspects of field theories, stochastic quantization methods,supersymmetry phenomenology and the quantization of discrete systems. The results were reflected in nearly one hundred articles published in international journals. Eight PhD. theses were completed in the group. In 1970 and 1973 c.nd 1986 three Argentine symposia on fields and particles were organized in Bari loche and attended by local physicists interested in the subject as well as a few invited from abroad. ?..2. Cooperation Agree me .its: The International Centre for Theoretical Physics in Trieste has had an important role _n tho formation of the first members of try group, as well as in thi.- updating of th«; research Fjubjects through t ho associat.eship scheme in which two particle physicists of Bariloche are currently taking part. - 106 - From the very beginning of its formal activity in 1968 the Barí loche group kept a strong collaboration with the group in La Plata through joint research, exchange of visitors and periodic meetings. Since 1970 the group also received the benefit of the visit of foreign experts sponsored by the OAS multinational program in physics. In 1978 a collaboration with the University of California at Santa Barbara was established on the basis of mutual visits with the support, of NSF and the CONICET. The same kind of cooperation is currently taking place with the Universidad Autónoma de Barcelona, thanks to the favourable attitutde of the Spanish government. Other important cooperation agreements with visits to and from CÜ:RN and the universities of Rome, Naples, Paris, Marseille, Madrid, taragoza, Catholic University of Rio de Janeiro, Sao Carlos, Sao Paulo and Mexico have been of great value. The group activity in the last two years has been supported by a grant from the CONICET. '¿.3. Meetings organized at Bar!loche: The Third Argentine Symposium on Theoretical Physics of Fields and Particles, dedicated to the memory of J.L. Agudin, was held from June 30th to July 12th, 1986, with the support of CONICET, CNEA, CLAF and ICTP. - 10 7 - The symposium was attended by 50 participants from Argentina, Brazil, Chile, Italy as well as by Argentine physicists living in the U.S.A., German Federal Republic and Italy. Professors R. Peccei (DESY, Hamburg), F. Rapuano and M. Virasoro (Rome University), G. Gelmini (Chicago University) and D. Boyanovsky (Stanford University) gave forty lectures and the rest of the participants seventeen communications. Two panel meetings on high energy research in Latin America and on Devoted Computers were also held. The group received the visits of professors C. Aragao de Carvalho (Pontificia Universidade Católica de Rio de Janeiro), C. Viallet (Paris), A. Malbouisson and F.R.A. Simao (Centro Brasilerio de Pesquisas Físicas de Rio de Janeiro) and C. Garcia Canal. H. Fanchiotti, L. Epele and H. Vuco*ich (Universidad Nacional de La Plata (Universidad Nacional de La Plata), among others. 2. 4. Partici pat ion l_n \nternational meetings and visits abroad: Members of the group attended the First Franco-Argentine Colloquium on Theoretical Physics which was held in Buenos Aires from August 28 to September 5, 1986. L. Masperi visited Trieste, Italy, using the associateship to the International Centre for Theoretical Physics (ICTP) and subsequently went to the Physics Department of the Naples University, Italy, invited for a period of two months. - 108 - RESEARCH LINES A. Anomalies in Field Theory: The quantization of anomalous theories, i.e. those which break at the quantum level symmetries valid at classical level has been studied. These theories may become of great importance for the description of nature since the Standard Model for electro-weak and strong interactions, depending on the experimental determination of it:; fermionic content, might be an anomalous theory. The quantization of this kind of theory is analyzed both in the canonical formalism and in the path integral method. Also, the toi-mulation in terms of differential geometry has been considered to í'ivtí ii. certain unity to all anomalous phenomena. Research is also persued regarding quantization of theories with second class constraints which present ambiguities both in the anomalous models and in those for massive non abelian vector bosons. I?. Phenomenology of Supersymmetric theories: During this period, models derived from supergravity and superstririg theory at low energy were studied, with emphasis on the (atill undiscovered) bounds on top quark mass, which are obtained from them. A critical analysis of models with two families where the top qiirirk is eliminated from the formulation was also performed. The results obtained so far show not only that the top quark is necessary for- the consistency of tne models but also that its mass must be lower than lOOHoV. Therefore, the next generation of accelerators should - 109 - make evident whether or not the theories under study describe physical reality. C. Singular Lagrangians and constrained canonical systems: The central problem refers to the canonical structure and the quantization of theories of arbitrary order. The Lagrangian formulation for these theories does not present major difficulties and its different classical equivalence classes are well defined. However, this is not true for the associated canonical structure and for the quantization concept. All theories of order different from the second are necessarily singular, and though methods to treat them are available, such as the Dirac procedure, they are not free from problems and ambiguities (as is shown e.g. in the anomalous theories). - Ill - 4. CONFERENCES AND PUBLICATIONS 4.1. Conferences: 4.1.2. Domestic Conferences - 71a REUNION DE LA AFA, Córdoba, October, 1986: "Corrientes Topológicas y Condiciones Subsidiarias para Teorías de Campos en Formalismo de Primer Orden" L. Masperi, F.D. Mazzitelli. "Ruptura Espontánea de la Paridad R en Modelos de Supergravedad (N = 1) a Bajas Energías" M.S. Carena, C.E.M. Wagner. - 72a REUNION DE LA AFA, BarJloche, September, 1987: "Renormal lzación de Masa y Causalidad en la Dinámica de una Carga Puntual Clásica" R. Montemayor. "Un Enfoque Alternativo para la Ecuación de Schrodlnger: Operadores de Desplazamiento entre Espacios de Hilbert" R. Montemayor. "Sobre la Cuantización de Teorías Anómalas" R.C. Trinchero. "Comparación de Métodos de Cuantlficación para Modelos Quirales Anómalos" A. Delia Selva, L. Masperi, G. Thompson. "Teoría No Abellana para Bosones Vectoriales y Cuantificación Canónica" M. Carena, C.E.M. Wagner, L. Masperi. 4.2. Invited Talks: L. Masperi gave a talk on Cuant if icación de Teorías de Campos con Vínculos de Segunda Clase at ICTP (Trieste), at the University of Sofia, Bulgaria and at the University of Naples, Italy. 4.3. Doctoral dissertations: "Soiltones en Teoría de Campos" F.D. Mazzitelli. Scientific Advisor: L. Masperi (December, 1986). - 112 - •\. Publ i cat ions: "FIRST OKDER PHASE TRANSITION IN LATTICE QCD AT FINITE TEMPERATURE WITH LIGHT FERMfONS: AN ANALYTIC STUDY" E. Dagotto, A. Moreo, R. C. Trinchero. Physical Review D33, 1121 (1986). "CORRELATION FUNCTIONS OF THE ANTIFERROMAGNETIC HEISENBERG MODEL USING A MODIFIEn LANCZOS METHOD" E.R. Gagliano, E. Dagotto, A. Moreo, F. Alcaraz. Physical Review B34, 1677 (1986). "DECONFINEMENT AND CHIRAL SYMMETRY RESTORATION" R.C. Trinchero. Physical Review D34., 3138 (1986). "AnLER-WEISBERGER SUM RULE AND HADRONIC MODELS" K.I). Mazzitelli, L. Mas.oeri. Physical Review D35, 368 (1987). "LOW ENERGY SUPERGRAVITY: R-PARITY AND THE TOP QUARK MASS" M. Carena, C.E.M. Wagner. Phy:;ics Letters Bi.86, 3ul (1987). "COMMENT ON 'NEW M0D2L OF b QUARK INTERACTIONS: A SUPERSTRING ALTERNATIVE'" J. Russo, C.E.M. Wagner. Physical Review Letters 58, 1380 (1987). "NKUTRALINO PRODUCTION .N e+e~ ANNIHILATION" M. Carena, C.E.M. Wagner. J-'hy.sics Letters B19B, 599 (1987). "AN ALTERNATIVE APPROACH TO THE SCHRODINGER EQUATION SHIFTING OPERATORS BETWEEN HILBEHT SPACES" H. Mont.emayor Physical Review A36, lfitíS? (1987). "LIMIT ON THE TOP QLARK MASS WITHIN THE FRAME OF THE MINIMAL SUPERSTRING INSPIRED MOJEL" M.S. Carena, C.L.M. Wagaer. Physics Letters B (to be published). "NON ABEÍ.IAN THEORY FOR MASSIVE VECTOR BOSONS AND CANONICAL QUANTIZATION" M. Carena, C. E. M. Wagner, L. Masperi Physical Review D (to be published). THEORETICAL PHYSICS NUCLEAR PHYSICS STAFF Scientists IB Graduate Student M. O. Cáceres L. D. Salem ++ P. Alemany M. E. Spina H. S. Wio * * CNEA/CONICET Researcher ++ CONICET Fellow - I 1 •> — •f>.. GENERAL DESCRIPTION Research in this group is related to the statistical mechanics of nuclear processes, and to non-equilibrium statistical mechanics in general. 2.2. Cooperation Agreements: There are some cooperation agreements with other theoretical groups. The group is in contact with the following institutions: - institut für Theoretische Physik, Physik Department, Technischen Universitát München, Munich, W. Germany. - KAMAF, Un:versidad Nacional de Córdoba, Córdoba, Argentina. - Depart.ement. de Ihysiqae Nucleaire, CE. N. Saclay, France. - Dipartimento di Fisica, Universita di Catania, Italy. Departament de Paysique Theorique, Univorsite de Geneve, Switzerland. - Service de Chimie Phy.,ique, Universite Libre, Brussels, Belgium. - Departamento de Física Teórica, Universitát de les Ules Balears, Palma de Mallorca, Sp^in. - Departamento de Físico., Universidad de Cantabria, Santander, Spain. - 116 - - Indian Statistical Institute, Calcutta, India. - 117 - 3. RESEARCH PROGRAMS A. Nuc1ear Dynamics: Research in nuclear dynamics is focussed on the study of processes that because of their characteristics call for a description in the framework of statistical mechanics and transport theory. Generally speaking they can be classified as: - Large amplitude nuclear motion of dissipative character, ie. nuclear fission and deep inelastic collisions between heavy ions. - Small ¡amplitude collective motion as found in giant resonances. The many body character of such problems makes necessary a deeper understanding of non-equilibrium kinetic and transport theories. The following problems nave been considered so far: - Giant resonance dynamics through the nuclear Vlasov equation. Normal modes frequencies and strength fragmentation as well as f.he characteristic motion have been obtained in this way. Selfconsistency and finite size effects have also been studied. Quantum effects are completely disentangled so semiclassical approximations can be tested. - 118 - - Description of collective nuclear motion through fluidodynamical models. Comparison with the hydrodynamic, viscoelastic and elastic regime (zero sound): the criteria for a particular truncation of the transport equations have been analyzed. - Solutions of the Fokkei—Planck equation in relation with nuclear fission in the framework o£ linear response theory. Also the study of competition between emission of light particles and fission. B. Non-equi1ibrium Stat istical Mechanics: Theoretical researcn on non-equilibrium processes consists mainly of studies within transport types of approach. Tht= analysis of fluctuations in stable and unstable systems is also investigated in order to study their non-equilibrium structure. Processes under" study: - Transport in disordered media in the context of linear response theory by using a mesoscopic description of the velocity-velocity autocorrelation function. - Elimination of variables in the context of non-Markovian stochastic processes in order to understand the problem of dynamic vs. static disorder. - Elimination of variables in the Fokker-Planck equation and - 119 -¡m in stochastic processes in general, based on influence functional methods. Path integral types of approach for the study of the colored noise problem, as well as in reaction-diffusion problems. Markovian chairs with internal states have been considered in order to study the incoherent intermediate scattering function of classical systems (such as superionic conductors). The study of fluctuations in cosmological problems, and the analyses of stability in the Robertson-Walker regime against stochastic perturbations have been studied. - 121 - 4. CONFERENCES AND PUBLICATIONS 4.1. Conferences: 4.1.1. International Conferences - IX WORKSHOP ON NUCLEAR PHYSICS, TANDAR, CNEA, Buenos Aires, Argentina, June 23 - July 4, 1986: "On the Vlasov Equation for Nuclear Collective Motion: A Functional Approach" L.D. Salem. H.S. Wio, M.E. Spina. "Fluid-Dynamical Description of Giant Resonances: Inclusion of Two-Body Collisions". L.D. Salem, M.E. Splna, H.S. Wio. - SIMPOSIO LATINOAMERICANO DE RELATIVIDAD Y GRAVITACIÓN, CBPF, Rio de Janeiro, Brazil, 1987: "Stochastic Perturbations in Friedman Robertson Walker Universes" M.O. Cáceres, M.C. Diaz, J.A. Pullin. INTERNATIONAL WORKSHOP ON INSTABILITIES AND NON-EQUILIBRIUM STRUCTURES, Universidad Federico Santa María, Valparaíso, Chile, December, 1987: "The Continuous-lime Resolvent Matrix for Non-Markovlan Chains" M.O. Cáceres, CE. Budde. "Marginal Distribution of Non-Markovian Stochastic Processes with Interna] States" C.E. Budde, M.O. Cáceres. 4.1.2. Domestic Conferences 71a. REUNION DE LA AFA, Córdoba, October, 1986: "Ecuación de Vlasov para el Movimiento Nuclear Colectivo: Un Método Funcional" L.D. Salem, H.S. Wlo. M.E. Spina. "Función de Autocorrelaclen de la Velocidad en Sistemas con Desorden Líquido" M.O. Cáceres. "Descripción Fluidodinámica de Resonancias Nucleares Gigantes: Inclusión de Colisiones de Dos Cuerpos" L.D. Salem, M.E. Spii -, H.S. Wio. la REUNION DE TRABAJO SOBRE MECÁNICA ESTADÍSTICA DEL DESEQUILIBRIO Y FÍSICA NO-LINEAL, Universidad Nacional de Lujan, Argentina, November, 1986: "Propiedades Aslntóticas en una Cadena no Markoviana" - 122 - M.O. Cáceres. "Descripción Cinética Reducida Mediante el Formalismo de Funcionales de Influencia" H.S. Wio, CE. Budde, C. Briozzo. "Eliminación de Variables Rápidas" H.S. Wlo (Invited Talk) - 72a REUNION DE LA AFA, Barlloche. September, 1987: "Descripción de Modos Colectivos en un Modelo Esquemático" L.D. Salem, H.S. Wlo. "Autoestados en la Representación de Wigner de la Mecánica Cuántica" L. D. Salem. - 2a REUNION DE TRABAJO SOBRE MECÁNICA ESTADÍSTICA DEL DESEQUILIBRIO Y FÍSICA NO-LINEAL, Universidad Nacional de Lujan, Argentina, December, 1087: "Estabilidad de un Universo de Robertson-Walker ante Perturbaciones Estocásticas" C.B. Brlozzo, CE. Budde, M.O. Cáceres, D. W. Lamberti. 4.3. Doctoral Dissertations: "Teoría de "Random Walks" en Redes. Su Generalización a Esquemas con Estados Internos" M.0. Cáceres Scientific Advisor: H.S. Wio (November, 1986). .<1. Puhlications: "ON THE NUMERICAL EVALUATION 01 Till-: I tYNMAN PROPAGATOR" I.. I). Salem, U.S. Wlo. Physios Letters AJJl. 1*'H M'.IW; I. "THE TWO DIMENSIONAL. SOI.UHLK MODEL FOR THE EXCITATION OF ROTATIONAL STATES IN DEFORMED NUCLEI" M. Bernath, D. R. Ben, M. Sfii-irono, M.I'!. Spina. Journal of Physics V,V¿, ]?.ü'.i (lliHH). "COUPLED GENERALIZED MASTER EQUATIONS FOR BROWNIAN MOTION AN I SOTROF11 CALI .Y SCATTERED" M.O. Cáceres. Physical Review AX3, 647 (ISSHj. "A NON-MAHKOVIAN LORENTZ GAS MODEL" M.O. (YircM-es. I nst al)i 11 ties and Nonequi 1 Ibr i um St.r-uctures, Eds. E. Tirapegui mid J. Villar-roe], 1). Reidel Publ. Co. (1987). "MUID DYNAMICAL. DESCRIPTION OF GIANT RESONANCES: INCLUSION OF TW0-130DY COLLISIONS" L.I). Salem, H.S. Wlo, M. E. Splna. Pr-oc. IX Workshop on Nuclear Physics; Eds. A.I). Machiavelli, H. M. Solía, E. Ventura (World Scientific, Singapore, 1987). "ON THE VLASOV EQUATION FOR NUCLEAR COLLECTIVE MOTION: A FUNCTIONAL APPROACH" L.I). Salem, H.S. Wlo, ME. Spina. Pi-oc. IX Workshop on Nuclear Physics; Eds. A.D. Machiavelli, H. M. Soria, E. Ventura (World Scientific, Singapore, 1987). "NON-MARKOVIAN DIFFUSION-1. IKE EQUATION FOR TRANSPORT PROCESSES WITH AN ISOTROPIC SCAT PERING" M.O. Cácores, U.S. Wlo. I'hysica A.142, !S(>:i (1987). "STOCHASTIC PROCESSES IN COSMOLOGY" M.A. Cáceres, M.C. Díaz, J. A. Pull in. Physics Letters A123, 3?,9 (1987). "MARGINAL DISTRIBUTION OE A MARKOVIAN CHAIN WITH INTERNAL STATES: THE RESOLVENT MATRIX" M.C. Cáceres, CE. Budde. Physics Letter-H A125, 369 (1987). "ON THE PROBLEM OF FREE-JUMP DIFFUSION WITH SUBLATTICE DISORDER" M.O. Cáceres. Physica Scripta (to be published). "RANDOM WALK THEORY FOR NEUTRON TRANSPORT WITH HIGH ANISOTROPIC SCATTERING" M.O. Cáceres. Reactor Physics for Developing Countries and Nuclear Spectroscopy Research, Ed. Medruno l.ieb (World Scientific, Singapore (to be publi shed). - 125 -•/las THEORETICAL PHYSICS SOLID STATE 1. STAFF Scientists IB Graduate Students B. Alascio * A. Aligia * D. Domínguez R. ATI L **°° J. Garcia Lorenzana Allub C. Balseiro G. Mato A. Caro * J. Sofo G. Chiappe + E. Gagliano ++ V. Griinfeld A. Lopez Dávalos M. D. Nunez Regueiro ** G. Ortiz ++ C. Proetto A. Rojo 4+ J. Simonin ** C. Wiecko ** CNEA/C0N1CET Researcher CONICET Researcher CNEA Fellow CONICET Fellow CONICET International Fellowship (1987) ICTP Fellowship (1987) von Humboldt Fellowship (1986 / June 1987) - 127 - 2. GENERAL DESCRIPTION The Theoretical Solid State Croup, formed in the early 70's, ha-; today a permanent staff of seven CNEA scientists, four CONICET members and several PhD students on CNEA and CONICET fellowships. 2. 1 Facilities: In addition to access to the Computer Center through remoto terminals there are a number of personal computers with peripherals available. 2.2 Cooperation Agreements: Members of the group have actively participated in joint research programs with individuals as well as with Scientific Centers in Brazil, Mexico, Germany, France and the U.S.. A joint project through the NSF-CONICET cooperation agreement has been operative for a number of years with over fifteen published papers on Superconductivity and Superconducting networks. Some of the Scientists of this group are Associate Members of the [CTP (Trieste, Italy). Their periodic visits provide fruitful contact with researcher?; in many other countries. - 128 - 3. RESEAP.CH PROGRAMS Current research in theoretical Solid State Physics spans a wide range of problems involving recent trends in the magnetic and superconducting properties of materials, quantum wells, intermediate valence and heavy fermions as well as disordered systems. The recent surge of experimental work on high T superconductivity has promoted increased discussion and a highly Interactive approach both within the group and with experimentalists in related fields (particularly low temperature and materials science). In what follows we summarize the different lines of research currently followed. A. Intermediate Valence: 1) A deeper analysis has been made of a previous model which relates the structure of the 4f photoemission spectra of rare earths to the Coulomb interaction between f and d states (including hybridization to an order of approximation such that the Kondo resonance is correctly reproduced at the appropriate limits). The influence of temperature, position of the 4f level and hybridization have been studied along the series of rare earths. High resolution XPS results were analyzed through a model which includes the degeneracy of the 4f states and the spin orbit splitting. 2) Intermediate valence in a disordered alloy has been described 129 using the "breathing shell" model. Phonon dispersion relations in superconducting SSm Y compounds were obtained which led to an interpretation for the presence of a mode in the gaps and the largu band widths observed within it. 3) The thermodynamics of an intermediate valence model with valence fluctuations between two magnetic configurations has been studied using the Bethe ansatz. 4) Superconducting properties of heavy fermions have been investigated starting from Anderson's model and a conventional (BCS) pairing for the electrons. B. Disordered Systems and LocalIzation: 1) EIGENSTATES AND TRANSMISSION COEFFICIENTS: Models corresponding to a tight binding Hamilt.onian or a discrete wave equation (Schrodinger's in particular) were applied to study the; motion of a particle in a disordered (non translational1 y invariant) medium. Random, incommensurate and polar (electric field creating a preferred direction) cases were considered. For random 1-d models anomalous behaviour of the localization length in the presence of non diagonal random disorder was found at the center of the band as well as several packets of localized states. A new algorithm was developed to calculate the physically relevant eigenstate. For Incommensurate models "connected packet" type states have - 130 - been found in the metal insulator transition region, which are currently being studied in more depth. Similar results were later obtained by Dr. M. Weissmann in CNEA (Buenos Aires). For models with an electric field present an approximate analytic solution was found for the transmission coefficient. The existence of potentially localized states has also been established. 2) FRACTALS: The models described above were also studied using fractal and multrifracial analysis. In particular, by postulating a fractal character for the tight binding hamiltonian of a finite hypercubic system a regular hierarchical tree was found for the eigenstates, with dimensions indicating the successive "generations". This leads to a simple algorithm for the densities of states in any dimension. This may be extended to strips or ',ars through a fractional dimension associated with the bandwidth. This fractal description makes it possible to correlate this model with the Parlsi ansatz of spin glass theory in tight binding language. Currently work is being done on an extension of the algorithm for disordered systems in 2D and 3D. 3) DEFECTS IN METALS: Basic studies centered on disordered alloys, including: i) Lattice dynamics with dislocations in the snapping bonds model in order to analyze: a) the spectrum of phonons emitted by moving - 131 - dislocations and the appearance of resonant mass Impurity modes-, b) The hardening/softening due to the presence of non diagonal impurities. ii) Study of the electronic structure of defects using the self consistant HUckel model In order to derive interaction potentials. The objective is to use the latter in molecular dynamic calculations of the properties of complex defects such as dislocations. C. Superconductivi ty 1) SUPERCONDUCTING FILAMENTARY ARRAYS (SUPERCONDUCTING NETWORKS); i) Planar- geometries of supereondurt i ng wires were studied f " I lowi np, the de Gennüs Alexander formulation for different geometries and degrees oí' disorder. Some of these results were experimentally verified In other1 laboratories nhroad. For disordered f^ystems the possibility was raised of a novel type of superconducting material with a percolating regime, whose phase diagram and critical exponent were obtained. ii) Multilayer structures: A theoretical formulation was mad« for systems consisting of alternating layers of two superconducting materials. The Ginzburg Landau theory was extended for the case of several super-conductors in contact which checked with experimental results not explained previously. - 132 - ill) Quantum effects in multiply connected superconducting systems, with po ;sible extensions to superconducting networks and granular superconductors: A systematic study of quantum interference phenomena in circuits with and without Josephson junctions was begun. Using the non-linear Ginzburg-Landau equations It is possible to investigate the response of multiply connected superconducting systems to injected external currents in the presence of a magnetic *^eld. One particular result is that a superconducting ring of dimensions of the order of the coherence length, with or without the application of externa! currents, behaves in a fashion similar to a SQUID with Josephson junctions. The study was extended to the case of symmetrical rings with four Josephson Junctions and two independent injected currents. The superconducting-normal phase dla; -am obtained for this system differs from the previous case (one single current) in that a modulation of the phase boundary Is possible by varying one of the applied currants. 2) SUPERCONDUCTIVITY AND RANDOM DISORDER Localization theory deals with the change of normal electrons from extended to localized states. A recent question is whether superconductivity is possible in insulators and whether both transitions (superconducting-normal and metal insulator) may occur simultaneously. Following Ma and Lee we have studied the effect of disorder (in Anderson's description: random diagonal tight binding) on -Ill superconducti vi t.y (described with local pairing in Bogolubov' •.-. formalism). The model was solved in two approximations: a) Narrow bands: Insulating limit, with a lowering of T with disorder. This agrees with some experiments on sheet geometries. b) Building a macromolecule inmersed in a sea of normal electrons: this is a simplified model for granular superconductors. We a::rumc all sites connected to each other with the same overlap -as- in <:;>i(i glasses-. This leads to an initial increase in T due to disorder (t.h'- band Is shifted). The effect, is somewhat similar to the variable band occupation found in llubbard type extended models for hiKh ', supfM'conduct. i v j l.y. We also used a mean field approximation for the overlap term to ;>1 u I tu' phase fj t :ipi-;>in shows both Hiip'TConduct i rig insulator - normal insulator' find sup'n:onducl.or~normal metal -- normal ihsuialor transitions, depending on the ratio between the attractive coupling which causes super-conduct i vi t.y and the site coupling which describes one particle transport. Beth transitions are simultaneously present only for a given ratio of the hopping and superconducting paramot "i-:;. We note that T 's are much larger- for the insulating regime, a I set which might be relevant to high T phenomena. 3) IIÍCH T - SUiriCONIJUCTÍNG CKRAMÍCS: c We studied superconducting mechanisms in these systems as will as ordering of oxygen vacancies in YBa Cu O . Attractive interactions were found for the latter in an excitonic model. - 134 - Another approach (In collaboration with other groups) has been to study a tight binding - weak correlation model with conventional electron-phonon interactions. D. Low Dimensional Systems 1) Some new results were found from the numerical calculations on the fractional quantum Hall effect with explicit consideration of the Hall electric field. The ground state properties were analyzed for different occupation schemes of the 1st Landau level. 2) A microscopic justification for the existence of molecular states In metals with structural Instabilities was begun. Such states make possible a phenomenological explanation for the resistivity, thermal conductivity and magnetic susceptibility of a large family of compounds: A-15, C-15 and transition metal dichaicogenides. E. Surfaces In collaboration with other groups abroad, we have studied magnetic properties, chemlsorption energy, relaxation and surface reconstruction of systems consisting of an adsórbate such as oxygen or nitrogen on transition metal surfaces, using strong binding modes in the Hartree-Fock approximation and Born-Mayer type repulsive potentials. F. Charge Density Waves We have studied: - 135 - 1) Effect of large magnetic fields on the charge density wave structure in Nb Se and similar systems. 3 2) New non linear effects in transport properties of systems with charge density waves. 3) Effect of electronic correlations on charge density waves. - 137 - 4. CONFERENCES AND PUBLICATIONS 4.1 Conference: 4.1.1. International Conferences - INTERNATIONAL CONFERENCE ON ANOMALOUS RARE EARTHS AND ACTINIDES, Grenoble, France, 7-11 July, 1986: "4f Photoemission from Light Rare-Earth Systems: f-d Coulomb Interaction and the Abrikosov-Suhl Resonance" M.D. Núñez Regueiro, M. Avignon. "Bethe-Ansatz Solution of a Model for a Mixed Valent Impurity with Two Magnetic Configurations: Charge Fluctuations and Thermodynbamic Properties" A.A. Aligla, C.A. Balseiro, C.R. Proetto, P. Schlottmann. "Sound Attenuation in Superconducting Intermediate Valence Systems" A. A. Allgia, O.L.T. de Menezes. - STATPHYS 86, Boston, U.S.A., 1986: "Superconductive Micronetworks" A. López, J. Slmonln. - YAMADA CONFERENCE XV ON PHYSICS AND CHEMISTRY OF QUASI-ONE DIMENSIONAL CONDUCTORS, Lake Kawaguchi, Yamanaski, Japan, 1986: "The effect of Magnetic Fields on the Electronic Structure of Density-Wave Systems" L. M. Fallcov, C.A. Balseiro. - SIMPOSIO DE FERMIONES PESADOS, Trieste, Italy, 11-18 July, 1986: "Bethe-Ansatz Solution of a Model for a Mixed Valent Impurity with Two Magnetic Configurations: Charge Fluctuations and Thermodynamic Properties" C.A. Balseiro, C.R. Proetto, P. Schlottmann. "Sound Attenuation in Superconducting Intermediate Valence Systems" A.A. Allgia, O.L.T. de Menezes. "4f Photoemission from Light Rare-Earth Systems" M.D. Nunez Regueiro, M. Avignon. 5th INTERNATIONAL CONFERENCE ON VALENCE FLUCTUATIONS", Bangalore, India, 5-9 January, 1987: "Effect of f-d Coulomb Correlations and Many-Body Resonance in Intermediate Valence Systems: f-Photoemlssion" M. D. Núñez Regueiro, M. Avignon. - SÉPTIMA CONFERENCIA SOBRE MATERIA CONDENSADA DE LA SOCIEDAD DE FÍSICA EUROPEA, Pisa, Italy, 7-10 April, 1987: "Tight-Binding Model for High T Superconductivity" c - 138 - A.A. Aligia, M. Kulic, V. Zlatic, K.H. Bennemann. "Chemlsorption Geometry of Oxygen on Ni(lOO)" A. A. Aligia, S. Reindl, K.H. Bennemann. - REUNION DE DISCUSIÓN SOBRE MATERIALES SUPERCONDUCTORES CON ALTA TEMPERATURA DE TRANSICIÓN, Strasbourg, France, June 3, 1987: "Tight-Binding Model for High T Superconductivity" A. A. Aligia, M. Kulic, V. Zlatic, K.H. Bennemann. - WORKSHOP ON NONLINEAR CHARGE DENSITY WAVES, ICTP, Trieste, Italy, May - June, 1987: "Unusual Wave-Functions in the 1-d Aubry Model" C. Wiecko. - EUROPEAN CONFERENCE ON INTERNAL FRICTION AND ULTRASONIC ATTENUATION IN SOLIDS, Amberes, Belgium, July. 1987: "Solution Hardening in Disordered Alloys: A Lattice Dynamics Approach" S. Ramos de Debiaggi, A. Caro. - INTERNATIONAL CONFERENCE ON HIGH T SUPERCONDUCTORS, ICTP, Trieste, c Italy, July, 1987: "Solution Hardening in Disordered Alloys: A Lattice Dynamics Approach" S. Ramos de Debiaggi, A. Caro. "Increase of T by Disorder" R. Allub, A. Caro. C. Wiecko. - INTERNATIONAL SUPERCONDUCTIVITY ELECTRONICS CONFERENCE (ISEC *87), Japan, Augus t, 1987 : "Analysis of a Four Josephson Junctions Variable Squid Circuit" H.J. Fink, V. Grünfeld, E.M. Roberts. - ECIFUAS, Belgium, 1987: "Solution Hardening in Disordered Alloys: A Latlce Dynamics Approach" S. Ramos de Debiaggi, A. Caro. - SECOND EUROPEAN WORKSHOP ON CHARGE DENSITY WAVES, Aussois, France, September, 1987: "Effect of Local CDW Instabilities on the Properties of Metals: a Simplified Exactly Sovable Model" G. Ortiz, M.D. Nunez Reguelro, M. Núñez Regueiro, B. Alascio. 4.1.2. Domestic Conferences WORKSHOP SOBRE DENSIDAD DE ESTADOS, LOCALIZACION Y CONDUCTIVIDAD EN SISTEMAS DESORDENADOS, Buenos Aires, Argentina, August, 1986: "El Método de Declinación Aplicado a Localización" C. Wiecko. - 139 - - 71a REUNION DE LA AFA, Córdoba, October, 1986: "Transición de DelocalIzación en Sistemas Unidimensionales Desordenados con Campo Eléctrico" D. Castello, A. Caro. Transición de Peierls en Conductores Unidimensionales AnIsotTópicos" E.R. Gagliano, C.R. Proetto, C.A. Balseiro. "Efecto Túnel Resonante en GaAlAs-GaAlAs: Influencia del Campo Magnético" C.R. Proettc, C.A. Balseiro. "Solución Analítica de un Sistema Unidimensional Desordenado con Campo Eléctrico" D. Castello, A. Caro, A. López. "Endurecimiento en Soluciones Sólidas Desordenadas" S. Ramos de Debiaggl, A. Caro. "Endurecimiento por Solución de Aleaciones Diluidas: Aproximación por Dinámica de Redes" A. Caro, S. Ramos de Debiaggl. "Efectos del Campo Eléctrico en el Efecto Hall Cuántico Fraccionarlo" G. Chlappe, A. Caro. "Efecto de Campo Magnético en la Estructura Electrónica de Sistemas de Ondas de Densidad" C.A. Balseiro. "Superconductividad y Desorden en el Modelo de Conectivldad de Rango Infinito" R. Allub, A. Caro, C. Wlecko. "Transición Neutral-Iónica en Compuestos Unidimensionales de Transferencia de Carga" E.R. Gagliano, C.A. Balseiro. "Efecto de la Repulsión Coulomblana entre Estados Extendidos y Localizados en el Modelo de Anderson: Grupo de Renormalización" R. Allub, C.A. Balseiro, B. Alascio. "Aproximación de Medio Efectivo para la Conductividad de un Sistema Ternario Desordenado" A.G. Rojo. "Funciones de Onda Inusuales en el Modelo de Aubry en 1-D" C. Wiecko. "Efecto Hall Cuántico Fraccionario" G. Chlappe, A. Caro. E.R. Gagliano, R. Allub. - REUNION DE LA SOCIEDAD ARGENTINA DE METALES, Buenos Aires, March, 1987: "Microscopía Acústica de Barrido" M. Caro, A. Caro. - 140 - - 72a REUNION DE LA AFA, Barí loche, September, 1987: "Interacción Electrón-Fonón en los Materiales Superconductores con Alta Temperatura Crítica" A. A. Aligia, M. Kulic?, V. Zlatic, K. H. Bennemann. "Geometría de la Quemisorción de Oxigeno sobre Ni (100)" A.A. Aligia, S. Reindl, K.H. Bennemann. "Propiedades Dinámicas de Sistemas de Muchos Cuerpos a T = 0" E.R. Gagliano, C.A. Balselro. "Fractalidad en Sistemas Unidimensionales Desordenados" G. Mato, A. Caro. "Efecto de Deformaciones Dinámicas Locales en Sistemas con Fuerte Acoplamiento Electrón-Fonón" G. Ortiz, M.D. Núfiez Regueiro, M. Núñez: Regueiro, B. Alascio. "Origen Cuántico de las Oscilaciones de Período Anómalo en la Magnetoreslstencia de Cilindros Metálicos" H. M. Pastawski, A.G. Rojo, C.A. Balseiro. "Efectos de correlación en la Estructura Electrónica de los Superconductores de alta T " A.G. Rojo, E.R. Gagliano, C.A. Balseiro, B. Alascio. "Distribución de carga en Heterojunturas de GaAs-AlGaAs en Presencia de un Campo Magnético Fxterno" J. Sofo, C.A. Balselro. 4.1.3. Invited Communications - INTERNATIONAL CONFERENCE ON ANOMALOUS RARE EARTHS AND ACTINIDES, Grenoble, France, July, 1986: "4f Photoemlssion from light Rare Earth Systems: f-d Coulomb Interaction and the Abrlkosov-Suhl Resonance" M. D. Núñez Regueiro, M. Avignon. - 5th INTERNATIONAL CONFERENCE ON VALENCE FLUCTUATIONS, Bangalore, India, January, 1987: "Effecto of f-d Coulomb Correlations and Many-Body Resonance in Intermediate Valence Systems: f-Photoemission" M. D. Núñez Regueiro, M. Avignon. - FRElE UNIVERSITXT BERLIN, Federal Republic of Germany, 1986: "Intermediate Valence Systems" A. A. Aligia. - INTERNATIONAL WORKSHOP IN CONDENSED MATTER, ICTP, Trieste, Italy, August, 1986: "4f-Photoemission from Rare Earths" M.D. Núñez Regueiro. - 141 - "Effect of Magnetic Fields In CDW Systems" C.A. Balseiro. INTERNATIONAL WORKSHOP IN CONDENSED MATTER, ICTP, Triest», Italy, July, 1987: "Wave Functions in Disordered and Incommensurate 1-d Models" C. Wlecko. 4.3. Doctoral Dissertations: "Redes Superconductoras" J. Simonin. Scientific Advisor: A. López (January, 1987). - 142 - 4.4. Publications: "FLUX PERIODICITY IN SUPERCONDUCTING RINGS: COMPARISON TO LOOPS WITH JOSEPHSON JUCTIONS" H.J. Fink, V. Grünfeld. Physical Review B33, 6088 (1986). "EFFECT OF COULOMB REPULSION BETWEEN LOCALIZED AND EXTENDED STATES IN THE ANDERSON MODEL" B. Alascio, R. Allub, C. A. Balseiro. Physical Review B34, 4786 (1986). "BETHE-ANSATZ SOLUTION OF A MODEL FOR A MIXED VALENT IMPURITY WITH TWO MAGNETIC CONFIGURATIONS: II, NUMERICAL SOLUTION OF THE THERMODYNAMIC EQUATIONS" A.A. Aligia, C.A. Balseiro, C.R. Proetto, P. Schlottmann. Z. für Physik B62, 311 (1986). "INTEGRABILITY OF A GENERAL MODEL FOR INTERMEDIATE VALENCE" A.A. Aligia, C.A. Balseiro, C.R. Proetto. Physical Review B33, t3476 (1986). "TRANSPORT IN A RANJOM CONDUCTING-INSULATING SYSTEM: A SIMPLIFIED APPROACH" A.G. Rojo. Physical Review A3JI, 651 (1986). "SEGREGATION AND SHAP¿ STABILITY IN SMALL BIMETALLIC PARTICLES" J.L. Moran, C.A. Baln-iro. Physical Review B33, ^849 (1986). "EFFECT OF HIGH MAGNETIC FIELDS ON THE ELECTRONIC STRUCTURE OF DENSITY WAVE SYSTEMS" C.A. Balseiro, L.M. F;.Uicov. Physical Review B34, 863 (1S36). "QUASI-ONE DIMENSIONAL DENSITY-WAVE SYSTEMS IN HIGH MAGNETIC FIELDS" C.A. Balseiro, L.M. Fulicov. Magnetic Properties of Low Dimensional Systems, Ed. by L. Falicov and J.L. Moran López, Springer Verlag, Heidelberg, 1986. "TRANSPORT PROPERTIES OF ONE DIMENSIONAL, DISORDERED TWO BAND SYSTEMS" M. Garcia, A.M. Llois, C.A. Balseiro, M. Weissmann. J. of Physics Cjj), 60ii3 (1986). "NEUTRAL IONIC TRANSITION AND DIMERIZATION IN ORGANIC MIXED-STACK COMPOUNDS" M. Avignon, C.A. Balseiro, C.R. Proetto, B. Alascio. Physical Review B33, 205 (1986). "DENSITY OF 4f-STATES IN RARE EARTHS COMPOUNDS" M.D. Núñez Regueiro, M. Avignon. J. of Magnetism and Magnetic Materials 54/57. 411 (1986). "POSSIBILITY OF CHARGE ORDERING IN INTERMEDIATE VALENCE SYSTEMS" M.D. Núñez Regueiro, M. Avignon. J. of Physics F16, 1121 (1986). I A 1 • "LOCALIZATION LENGTH AND FRACTAL DIMENSIONALITY FOR WAVE FUNCTIONS IN THE DISORDERED ANDERSON MODKI." E. Román, C. Wiecko. Z. für Physik B62, 163 (15J8B). "THEORY FOR SUPERCONDU!TIV1TY IN METALLIC MULTILAYER COMPOUNDS" J. Slmonln. Physical Review B33, 1700 (1986). "SURFACE TERM IN THl.- SUPERCONDUCTIVE GINZBURG-LANDAU FREE ENERGY: APPLICATION TO THIN FILMS" J. Simonin. Physical Review B33, 7830 (1986). "PERCOLATION IN SUPERCONDUCTIVE NETWORKS" J. Simonin, A. López. Physical Review Letters 56, 2649 (1986). "EFFECT OF f-d COULOMB REPULSION IN THE THERMODYNAMIC PROPERTIES OF ANOMALOUS RARE EARTH IMPURITIES" R. Allub, C.A. Balselro, B. Alascio. J. of Magnetism and Magnetic Materials 63/64. 539 (1987). "PEIERLS INSTABILITY IN SPINLESS ONE DIMENSIONAL CONDUCTORS" E.R. Gagliano, C.R. Proetto, C.A. Balselro. Physical Review B36, 2257 (1987). "CORRELATION EFFECTS IN THE ELECTRONIC STRUCTURE OF HIGH T c SUPERCONDUCTORS" E.R. Gagliano, A.G. Rojo, C.A. Balseiro, B. Alascio. Solid State Communications 64, 901 (1987). "DYNAMICAL PROPERTIES OF QUANTUM MANY-BODY SYSTEMS AT ZERO TEMPERATURE" E.R. Gagliano, C.A. Balseiro. Physical Review Letters 59, 2999 (1987). "LOCALIZATION IN ONE DIMENSIONAL DISORDERED SYSTEMS WITH ELECTRIC FIELD: AN ANALYTICAL APPROACH" D. Castello, A. Caro, A. López. Physical Review B36, 3002 (1987). "BREATHING SHELL ALLOY MODEL FOR THE PHONON DISPERSION RELATIONS OF INTERMEDIATE VALENCE Sm^^S" G. Pastor, A. Caro, B. Alascio. Physical Review B36, 1673 (1987). "VARIABLE SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE: THEORY" H.J. Fink, V. Grünfeld, S.M. Roberts. Physical Review B36, 74 (1987). "QUANTUM INTERFERENCE DEVICES WITHOUT JOSEPHSON JUNCTIONS" H.J. Fink, V. GrUnfeld, A. López. Physical Review B35, 35 (1987). "EFFECT OF OXYGEN ON MAGNETISM AT THE SURFACE OF CR(IOO)" A.A. Aligla, J. Dorantes Dávila, J.L. Moran López, K.H. Bennemann. Physical Review B35, 7CS3 (1987). - 144 - "ELECTRONIf STRUCTURE AND ELECTRON-PHONON INTERACTION FOR La M CuO 2-x x 4 SYSTEMS" A. A. Aligj-\. K.IL Bennemann, M. Kulic, V. Zlatic. Int. J. o: Modern Physics B1., 951 (1987). •'BFTHE-ANSATZ SOLUTION OF A MODEL FOR A MIXED VALENT IMPURITY WITH TWO MAGNETIC CONFIGURATIONS: CHARGE FLUCTUATIONS AND THERMODYNAMIr PROPERTIES" A. A. Aligia, C.A. Balseiro, C.R. Proetto, P. Sehlottmann. .1. of Magnetism and Magnetic Materials 63/64. 231 (1987). "4-f-PHOTOEMlSSlON FROM LIGHT RARE-EARTHS SYSTEMS: f-d COULOMB INTERACTION AND THE ABRIKOSOV-SUHL RESONANCE" M. II Núfioz Regueiro, M. Avignon. J. of Magnetism and Magnetic Materials B3/R4. 487 (1987). "EfTECT OF f-d COULOMB CORHF.LAT 1ONS AND MANY BODY RESONANCE IN IW1KRMEDIATK VALENCE SYSTEMS: f-PHOTOEMlSSION" M.0. Núfiez Reguoiro, M. Avignon. !'h"¡jret ical and Experimental Aspects of Valence Fluctuations, F.'d. '• .r. Gupta, S.K. Mil 1 5 k. Plenum Pross, Now York, 1987. 'S¡J! •!•!«! INDUCTlVir, AND RANDOM DISORDER IN THE ZERO BANDWIDTH LIMIT" C Wecko, R. Allub. ¡tiysf-al Review B35. 2041 (1987). ';rn A I lub, A. Caro. C. W,. ci-o. ::,;/sicnl Ro'-'lew B3B, 8823 O987). ¡;i 1-r.!M11.AFi DEPENDENCE ON DJ -IKNSION OF HAMILTONIANS ON ;1VP1'RCUHIC LATTICFiS :l M. Pru-.tawski , C. Wiecko. I >,s ir-al Itevíew A36, 5854 (1987). ":.)HM|i AITI.NTUATION IN SUPERCONDUCTING INTERMEDIATE VALENCE SYSTEMS" A '. ATp.la, 0.1..T. de Menezes. i of MiiRnotlsm and Magnetic Materials 63/64. 423 (1987). k DEPENDENT ENERGY GAP IN TWO BAND SUPERCONDUCTORS" •i ¡1' dp Menozes, A.A. Aligia. Ijipariesf? Journal of Applied Physics 26, 1231 (1987). "MO! ,TI FRACTAL WAVE FUNCTIONS IN ONE-DIMENSIONAL DISORDERED SYSTEMS' ; Mato, A. '*ar-o. / of Physics C20, 1.717 (1987). "IMFLUE::...': OF THE ELECTRIC FIELD ON THE FRACTIONAL QUANTUM HALL ¡"'¡•'¡•'¡•XT" n. Cl i S a ppe, A. Caro. Pl..vsic:ii Revipw B (to bo published). 1 I'i.MNONf. RADIATED RY MOVING DISLOCATIONS IN DILUTE ALLOYS" :;; íi.imo1: de Debiaggi, A. Caro. J of Physics (to bn published). "SOLUTION HARDENING IN DILUTE ALLOYS: A LATTICE DYNAMICS APPROACH" S. Ramos de Debiaggi, A. Caro. Physical Review B (to be published). "UNUSUAL WAVE FUNCTION IN THE AUBRY MODEL" C. Wiecko. Physica Scripta (to be published). "NEAR BAND CENTRE STATES FOR ONE-DIMENSIONAL OFF DIAGONAL DISORDERED SYSTEMS" H.E. Román, C. Wiecko. Z. fur Physlk B (to be published). "LOCALIZATION PROPERTIES IN LINEAR MODELS THROUGH DECIMATION" C. Wiecko, H.E. Román. Philosophical Magazine (to be published). "FINITE-SIZE STUDIES OF THE NEUTRAL-IONIC TRANSITION IN ORGANIC MIXED-STACK COMPOUNDS" E.R. Gag*iano, C.A. Balseiro, B. Alascio. Physical Review B (to be published). "DELOCALIZATION TRANSITION IN 1-D DISORDERED SYSTEMS WITH ELECTRIC FIELD" D. Castello, A. Caro, A. López. Physical Review B (to be published) "QUANTUM ORIGIN OF HALF-FLUX OSCILLATION IN THE MAGNETORESISTANCE OF METAL CYLINDERS" H.M. Pastawskl, A.G. Rojo, C.A. Balseiro. Physical Review B (to be published). 7 - APPERDIXBS APPENDIX I DEPARTMENT STAFF SCIENTISTS GRADUATE STUDENTS> ON FELLOWSHIPS ! TECHNICAL DIVISION L TECHNICIANS TOTAL OTHER AFPRENT. CNEA i CONICET I CNEA CONICET IB OTHER i I INST1TUT. 1 LOW TEMPERATURE (oo) 7 3 2 ,, 11 3 PHYSICS 2 23 i ¡ I ATOMIC 1 1 COLLISIONS 10 | 3 8 2 25 1 I (#) METAL PHYSICS 6 1 3 2 1 2 16 Í NEUTRON AND (#) 1 1 2 REACTOR PHYSICS 4 1 2 i: | i MAGNETIC (**) 2 1 RESONANCE 5 1 3 13 | ELEMENTARY TH E 2 2 1 2 2 12 PARTICLES 3 ORETIC A SOLID STATE 7 PHYSICS 4 _L 3 4 19 I 1 L PHYS I NUCLEAR 3 1 1 5 PHYSICS LO COMPUTATIONAL 1 4 L PHYSICS 2 1 r ,*) TOTA.. 7 4 ' • - 2 1 2 8 4 i 28 45 i - 150 - DEPARTMENT STAFF References: (*) : 11 of these scientists are also affiliated with CONICET. (#) : Argentine Army. (+) : Instituto Balseiro. (•>) : SECYT. : Universidad Nacional del Centro de la Provincia de buenos Aires. (**) : Under contract. (°°) : One is a SECYT fellow. (-H-) : ALTEC APPENDIX II VISITING SCIENTISTS DATE NAME FROM: INVITED BY: 1986: January Prof. Massico Di Toro Universita di Catania- Italy. Neutron and Reactor Physics January Dr. Giinter Staniek Deutsche Gesellschaft für Luft und Raumfahrt eV, Metal Physics Cologne, F.R.G. January Prof. Daniel Boy.°novsky Stanford University, California, USA. Theoretical Physics February Dr. Jacques J. P. Kappler Laboratoire de Magnétisme et Structure Électronique Low Temperature Physics des Solides, Strasbourg, France. February Prof. Antonio Méndez Vilaseca Universidad Autónoma de Barcelona, Spain. Theoretical Physics February Prof. Willy C. H. Benoit École Polytechnique Fedérale, Lausanne, Switzerland. Theoretical and Metal Physics February Prof. Angelo Delia Selva Universitá degli Studi, Naples, Italy. Theoretical Physics February Prof. Miguel G. Kiwi Pontificia Universidad Católica de Chile, Santiago, Theoretical Physics Chile. February Dr. Jorge E. Miraglia Instituto de Astronomía y Física del Espacio (IAFE), Atomic Collisions Buenos Aires, Argentina. February Prof. José R. Iglesias Universidade Federal do Rio Grande do Sul, Theoretical Physics Porto Alegre, Brazil. February Prof. Carlos Aragao de Pontificia Universidade Católica, Rio de Janeiro, Theoretical Physics Carvalho Brazil. February Prof. Miguel A. Lagos Pontificia Universidad Católica de Chile, Santiago, Theoretical Physics Chile. (1986) March Prof. Friedrich Noack Universitat Stuttgart, F.R.G. Magnetic Resonance March Dr. Julio Ferrón INTEC, Santa Fe, Argencina. Theoretical Physics March Prof. Gilberto Ferreira Fraga Universidade Federal do Rio Grande do Sul, Low Temperature Physics Porto Alegre, Brazil. March Prof. Horst Simonis and A.-L.-universitat Freiburg, F.R.G. Theoretical Physics Prof. Adriana S. de Simonis Georgia University, Athens, Georgia, USA. Atomic Collisions March Prof. Manuel G. Menéndez v University of Neb '•••'••.?. linooln3 Nebraska, USA. Atomic Collisions March Prof. Joseph Macek F.-A.-Universitat zu Erlangen-Nuremberg, F.R.G. Atomic Collisions April Prof. Ludwig E. G. Wedler Universidad Nacional de La Plata, Argentina. Low Temperature Physics I April Lie. Laura Damonte Universidad Nacional de Rosario and INTEC, Santa Fe, Theoretical Physics VJ1 April Prof. Rafael Calvo Argentina. May Dr. Mario C. G. Passeggi INTEC, Santa Fe, Argentina. Magnetic Resonance May Lie. Ricardo Steinmann and Universidad de Buenos Aires, Argentina. Low Temperature Physics Ing. Eduardo Pérez <¿odtke May Prof. Manuel Cardona Max-Planck-Institut, Stuttgart, F.R.G. Basic Research Dept. May Prof. Ana Celia Mota Eidgenossische Technische Hochschule, Zurich, Low Temperature Physics Switzerland. June Prof. Jean Delahaye CNRS, Paris, France. Basic Research Dept. June Ing. Luis A. Remez CNEA, Buenos Aires, Argentina. Neutron and Reactor Physics June Prof. Fernando Lund Universidad de Chile, Santiago, Chile. Low Temperature Physics June Prof. Vicente Torra Ferré Universidad de las Islas Baleares, Palma de Mallorca, Metal Physics Spain. (1986) July Prof. Eduardo Cesari Aliberch Universidad de Barcelona, Spain. Metal Physics July Prof. Roberto Piriz Universidad Nacional del Centro, Tandil, Argentina Atomic Collisions July Dr. R. C?lerazuck CENG, Grenoble, France. Low Temperature Physics July Dr. Roberto D. Rivarola Instituto de Física de Rosario, Argentina. Atomic Collisions August Dr. Horacio M. Pastawski INTEC, Santa Fe, Argentina. Theoretical Physics August Dr. Jorge Rosenblatt Institut National des Sciences Appliquées, Rennes, Low Temperature and France. Theoretical Physics August Prof. Anroine Salin Université de Bordeaux, France. Atomic Collisions September Prof. Marc J. M. Mézard École Nórmale Supérieure de Paris, France. Theoretical Physics September Prof. Ernst H. Brandt Max-Planck-Institut, Stuttgart, F.R.G. Low Temperature Physics September Prof. Eugenio Lerner Universidade Federal de Rio de Janeiro, Brazil. Low Temperature Physics VJ1 I September Dr. Aron Pinczuk AT & T Bell Labs, New Jersey, USA. Basic Research Dept. October Prof. Juan C. Gallardo Quantum Institute, University of California at Theoretical Physics Santa Barbara, USA. November Dr. Pierre G. P. Monceau CNRS, Grenoble, France. Magnetic Resonance, Low Temperature and Theoretical Physics November Dr. Jean P. H. Simon Laboratoire de Thermodynamique et Physique-Chimie, Metal Phvsics Saint Martin d'Keres, France. November Dipl.Phys. Jiirgen Kemmler J.W. Goethe-Universitat, írankfurL, F.R.G. Atomic Collisions November Dr. James Adney and NEC, Wisconsin, USA. Atomic Collisions Dr. Mark Sur.dquist November Prof. Carlos Ret tori Kstadual de Campinas, Sao Paulo, Brazil Marnetic Reson.ince (1986) November Lie. Alberto Ivolfenson FAMAF, Universidad Nacional de Córdoba, Argentina. Magnetic Resonance November Lie. Leonor A. Kirilovsky CNF.A, Buenos Aires, Argentina. Neutron and Reactor Physics December Dr. Guillermo Dussel, CNEA, Buenos Aires, Argentina. Theoretical Phypi :s Dr. Horacio Ceva and Dr. Guillermo Dukelsky December Prof. Carlos Tejedor Universidad Autónoma de Madrid, Spain. Basic Research Dept. December Prof. Hilda A.G. de Cerdeira Universidade ".stadual de Campinas, Sao Paulo, Brazil. Theoretical Physics December Prof. Fernando Cerdeira Universidade Estadual de Campinas, Sao Paulo, Brazil. Basic Research Dept. December Prof. Edwsrd H. Fradkin University of Illinois, Urbana, 111., USA. Theoretical Physics December Prof. J. Lazerowicz Universíté de Grenoble, France. Low Temperature Physics December Prof. Ney V. Vugman Universidade Federal de Rio de Janeiro, Brazil. Magnetic Resonance .e- December Prpf. Leopold Falicov University of California at Berkeley, USA. Basic Research Dept. December Prof. Herman J. Fink University of California at Davis, USA. Low Temperature and Theoretical Physics 1987: January Prof. Michel Baranger Massachusetts Institute of Technology (M.I.T.), USA. Neutron and Reactor Physics January- Prof. Coraci Malta Universidade de Sao Paulo, Sao Carlos, Brazil. Neutron and Reactor Physics January Prof. Jorge L. Alfaro Solís Universidad Católica de Chile, Santiago, Chile. Theoretical Physics January Dr. Christiaruí Korthals Altes CNRS, Marseilles, France. Theoretical Physics January Dr. Marcos Saraceno TANDAR, CNEA, Buenos Aires, Argentina. Neutron and Reactor Physics January Lie. Daniel E. Rodrigue? INTEC, Santa Fe, Argentina. Theoretical Phvsics (1987) January Dr. Rafael Calvo INTEC, Santa Fe, Argentina. Magnetic Resonance February Pr. Juan F. Weisz INTEC, Santa "e, Argentina. Theoretical Physics February Dra. María I. Flor it de Borzi INIFTA, Universidad Nacional de La Plata, Argentina. Atonic Collisions February Dr. Jorge E. Miraglia IAFE, Buenos Aires, Argentina. Atomic Collisions February Dra. María C. Palcos Proyecto Ciclotró:i, CNEA, Buenos Aires, Argentina. Neutron and Reactor PhysJ-=- February Prof. Francisco Claro Universidad Católica de Chile, Santiago, Chile. Basic Research Dept. February Prof. Luis Mendoza Celis Universidad de Buenos Aires, Argentina. Low Temperature Physics February Prof. José R. Fulco University of California at Santa Barbara, USA. Basic Research Dept. February Prof. Horacio C. Panepucci Universidade de Sao Paulo, Sao Carlos, Brazil. Magnetic Resonance February Ing. Francis Levy École Polytechnique Fedérale, Lausanne, Switzerland. Magnetic Resonance February Prof. Jan F. W. Slaets Universidade de Sao Paulo. Sao Carlos, Brazil. Theoretical Physics February Prof. Fernando Lund Universidad de Chile, Santiago, Chile. Low Temperature Physics March Prof. David Ríos Jara Universidad Nacional Autónoma de México, México. Metal Physics March Dr. R. Valenzuela Comisión Nacional de Investigaciones Espaciales, Atomic Collisions Buenos Aires, Argentina. March Dr. Hernán Bonadeo CNEA, Buenos Aires, Argentina. Basic Research Dept. March Dr. Gerhard Haerendel Max-Planck-Institut, Stuttgart, F.R.G. Atomic Collisions March Lie. Carlos Budde FAMAF, Universidad Nacional de Córdoba, Argentina. Neutron and Reactor Physics April Dr. Hernán Bonadeo CNEA, Buenos Aires, Argentina. Basic Research Dept. April Lie. Carlos Briozzo and FAMAF, Universidad Nacional de Córdoba, Argentina. Neutron and Reactor Physics Lie. Carlos Budde (1987) April Dr. Marcos H. Grimsditch Argonne National Laboratory, Illinois, USA. Basic Research Dept. April Dr. Andrés Kalnay Instituto Venezolano de Investigaciones Científicas, Basic Research Dept. (IVIC), Caracas, Venezuela. April Dr. Hans J. Herrmann Centre d'Études Nucléaires, Saclay, France. Theoretical Physics May Ing. Luis Mendonc.a Brandao Instituto Militar de Engenheria, Rio de Janeiro, Brazil. Metal Physics June Prof. Suzanne CM.de Cheveigné École Nórmale Supérieure de Paris, France. Low Temperature and Theoretical Physics June Dr. Mario Passeggi and INTEC, Santa Fe, Argentina. Magnetic Resonance Dr. Rafael Calvo July Dr. !ioberto Rivarola IFIR, Rosario, Argentina. Atomic Collisions July Prof.. Efraín Solarte Universidad Nacional de Bogotá, Colombia. Atomic Collisions July Prof,. Agnés Traverse CSNSM, Université de Paris-Sud, France. Basic Research Dept. ON I July Prof.. Saul B. Oseroff University of California at San Diego, USA. Magnetic Resonance July Prof.. Maximinc San Miguel Universidad de las Islas Baleares, Palma de Mallorca, Neutron and Reactor Physics Spain. August Prof.. Jorge V. José Northeastern University, Boston, OSA. Theoretical Physics August M. Lieven Cooreman Université de Louvain, Belgium. Metal Physics August Lie. Susana R. de Debiaggi Universidad Nacional del Comahue, Neuquén, Argentina. Theoretical Physics August Lie. Griselda Polla CNEA, Buenos Aires, Argentina. Low Temperature Physics August Lie. Carlos Budde and FAMAF, Universidad Nacional de Cordoba, Argentina. Theoretical Physics Lie. Carlos Briozzo August Dra. Delia A. de Widuczynski, CNEA, Buenos Aires, Argentina. Low Temperature Physics Lie. Marta Granovsly and Ing. Gustavo Galambos (1987) September Prof. Claude M. Viallet Université de Paris, France. Theoretical Physics September Dip.Phys. Wolfgang W. Morr R-K-Universitat Heidelberg, F.R.G. Low Temperature Physics September Dr. Miguel Octavio Instituto Venezolano de Investigaciones Científicas, Low Temperature Physics (IVIC), Caracas, Venezuela. September Prof. Roberto Nicolsky Universidade Federal de Rio de Janeiro, Brazil. Low Temperature Physics September Prof. Hervé R. Jouin Université de Bordeaux, France. Atomic Collisions September Dr. Iván K. Schuller Argonne National Laboratory, Illinois, USA. Basic Research Dept. September Prof. John D. Axe Brookhaven National Laboratory, USA. Basic Research Dept. September Dr. Juan F. Weisz INTEC, Santa Fe, Argentina. Theoretical Physics September Dra. Maria I. Florit de Borzi INIFTA, Universidad Nacional de La Plata, Argentina. Atomic Collisions September Lie. Carlos Briozzo FAMAF, Universidad Nacional de Córdoba, Argentina. Theoretical Physics 1 October Prof. Luis R. Migoni Universidad Nacional de Rosario, Argentina. Basic Research Dept. October Dr. John Gibbons Oak Ridge National Laboratory, Tennessee, USA. Atomic Collisions October Prof. Juan J. Giambiagi Centro Latinoamericano de Física, Rio de Janeiro, Theoretical Physics Brazil. October Lie. N. ilingolo Universidad de Buenos Aires, Argentina. Low Temperature Physics November Dr. Jean Michel Mignot CRTBT - CNRS, Grenoble, France. Low Temperature and Theoretical Physics November Prof. Luis R. Migoni Universidad Nacional de Rosario, Argentina. Theoretical Physics November Dr. Jean Pierre Rozet Institut Curie, Paris, France. Atomic Collisions November Dr. Hernán A. Bonadeo CNEA, Buenos Aires, Argentina. Theoretical Ph. s"Cf (1987) November Prof. Vicente Torra Ferré Universidad de las Islas Baleares, Palna de Mallorca, Metal Physics Spain. November Prof. Werner Oldekop Technische Universitat zu Braunschweig, F.R.G. Neutron and Reactor Physics November Prof. Alberto Gras Martí Universidad de Alicante, Spain. Atomic Collisions December Prof. José Lajzerowicz Université" de Grenoble, France. Low Temperature Physics December Dr. Horacio Ceva CNEA, Buenos Aires, Argentina. Theoretical Physics December Dra. Celia Saragovi de Badler CNEA, Buenos Aires, Argentina. Magnetic Resonance De .ember Dr. Jean Souletie CRTBT - CNRS, Grenoble, France. Low Temperature Physics December Prof. James Callaway Rockefeller University, New York, USA. Theoretical Physics oo - 15? - GLOSSARY A.A.T.N. : Asociación Argentina de Tecnología Nuclear AFA : Asociación Física Argentina ALTEC : Alta Tecnología S.E. (Bariloche, Argentina) CAB : Centro Atómico Bariloche (Argentina) CBPF : Centro Brasileiro de Pesquisas Físicas (Rio de Janeiro, Brazil) CENC : Centre d'Etudes Nucléairen de (¡renoble (France) CLAF ; Centro Latinoamericano de. Física (Rio de Janeiro, brazil) CNEA : Comisión Nacional de Energía Atómica (Argentina) CNRS : Centre National de la Recherche Scientifique (Grenoble, France) CÜNICET : Concejo N-scional de Investigaciones Científicas y Técnicas (Argentina) CRTBT : Centre des Recherches sur les Tres Basses Temperatures (Grenoble) D.I.D. : Dirección de Investigación y Desarrollo, CNEA (Argentina) E.A. ; Ejército Argentino FAMAF : Instituto de Matemáticas, Astronomía y Física (Córdoba, Argentina) IAFE : Instituto de Astronomía y Física del Espacio (Buenos Aires, Argentina) IB : Instituto Balseiro (Bariloche, Argentina) TCTP : International Centre for Theoretical Physics (Trieste, Italy) [FIR : Instituto de Física de Rosario (CONICET - UNR, Argentina) ÍNIFTA : Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas INSA : Instituí National des Sciences Apjliquées de Lyon (France) INTA : Instituto Nacional de Tecnología Agropecuaria (Argentina) INTEC : Instituto de Desarrollo Tecnológico para la Industria Química (Santa Fe) INT1 : Instituto Nacional de Tecnología Industrial (Buenos Aires, Argentina) INVAP : Investigación Aplicada S.E. (Bariloche, Argentina) KfK : Kernforschungs¿eiitrum Karlsruhe GmbH (F.R.G.) NSK : National Science Foundation (USA) OAS : Organization of American States PNUD : Programa de las Naciones Unidas para el Desarrollo SECYT : Secretaría de Ciencia y Técnica (Argentina) TANDAR : Tandem Argentino (CNEA, Buenos Aires, Argentina) TWAS : Third World Academy of Scisnces (Trieste, Italy) l!BA : Universidad de Buenos Aires (Argentina) UFRJ : Universidad Federal de Rio de Janeiro (Brazil) HNAM : Universidad Nacional Autónoma de México UNC : Universidad Nacional de Cuyo (Mendoza, Argentina) UNCPBA : Universidad Nac. del Centro de la Provincia de Buenos Aires (Tandil) UNLP : Universidad Nacional tie l.a Plata (Argentina) UNR : Universidad Nacional Je Rosario (Argentina)