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How a Scientific Discovery Is Made: A Case History

The case of high-temperature shows that discoveries have broad and deep root systems, hidden personal aspects, and lessons for science policy

Gerald Holton, Hasok Chang and Edward Jurkowitz

thoroughly investigate an informative A Brief History Even science in the has beenbest compared of times, to herd? managing case?the discovery of high-tempera? Superconductivity?the loss of electri? ing cats; it is not done well, but one is ture superconductivity?which, hav? cal resistance below a critical, or transi? surprised to find it done at all. In these ing occurred just 10 years ago, is recent tion, temperature (Tc) characteristic of days of diminishing resources, the enough to permit reconstructing its the material?was first discovered in analogy seems even more striking. Set? context. Our investigation, which in? mercury by the Dutch Heike ting priorities for research, choosing cluded interviews with Karl Alex Kamerlingh Onnes in 1911. Mercury be? which projects are to be supported and M?ller and Johannes Georg Bednorz, comes superconducting at just 4.2 de? which abandoned, triggers epic battles the who discovered the first grees above absolute zero (4.2 degrees at the highest levels. It requires pre? high-temperature superconductors, Kelvin). Teams large and small worked dicting which paths and which mix? throws light on a set of problems of in? for decades in the hope of finding elec? ture of policies might best advance sci? tense current interest: How does "cu? trical conductors with higher critical ence and lead to fruitful technologies. riosity-driven/' or basic, science interact temperatures, which would be easier Yet, in such debates, little attention is with "strategic" research and engineer? and cheaper to keep resistance-free. given to one of the most fundamental ing? How important are both planning There beckoned the rewards of both questions: What can historical cases and serendipity in discovery? What new theories to explain the phenome? teach us about what it takes to make a laboratory culture makes success more non and of practical applications to ex? scientific discovery? There are many likely? How deeply are the roots of ploit it; among the latter was the possi? popular ideas abroad, often based on crucial ideas and apparatus buried in bility of enormous new efficiencies in oversimplified textbook accounts of fa? the soil of history? How important is the transmission and use of electricity. mous discoveries and on charming the practice of borrowing across tradi? But nature, for a long time, yielded anecdotes. They have little to do with tions and disciplines? What role do the little hope for real progress. By 1973, the unruly complexity of the events private style and presuppositions of fully 62 years after the discovery of the themselves, and can only mislead sci? the individual play in research? phenomenon of superconductivity, all ence policymakers. Our study demonstrated that scien? efforts had stalled at a Tc of 23.3 Kelvin, For this reason, the authors of this tific innovation depends on a mixture the critical temperature of a niobium article welcomed an opportunity to of basic and applied research, on inter? germanium compound (Nb3Ge). After disciplinary borrowing, on an unforced years of frustrating failures to boost Tc pace of work and on personal motiva? into a region where there were realistic Gerald Holton is Mallinckrodt Professor of tions that lie beyond the reach of the prospects for commercial use, high and professor of the history of science at Harvard University. His most recent book, administrator's rule book. While many temperature superconductivity was no Einstein, History and Other Passions, deals of these findings may be familiar to longer considered a promising area. with the perennial fight over the place given to sci? students of scientific creativity, our op? Some theories held that no higher Tc ence in our culture. Hasok Chang is a lecturer in erational mode of analysis, which is could be expected. Bernd Matthias, a the philosophy of science at University College, roughly comparable to the methods of highly respected Bell Laboratories University of London. His main research interests genealogical research, makes them physicist who, together with collabo? include the history and philosophy of modern more precise, testable and generally rators, had discovered hundreds of physics, and the philosophical analysis of measure? ment methods in various sciences. Edward applicable. As such they may serve as new superconductors, challenged his an empirical complement to some of peers to give up "theoretically motivat? Jurkowitz, a postdoctoral fellow, is currently at the the untested assumptions that inform ed" searches, or "all that is left in this Institute f?r Wissenschaftgeschichte in Berlin, studying the history of quantum theory. policy discussions, especially the an? field will be these scientific opium ad? guished debates in Washington and in dicts, dreaming and reading one an? Address for Holton: Jefferson Physical Laboratory, other's absurdities in a blue haze" Harvard University, Cambridge, MA 02138. corporate boardrooms over the relative Internet: [email protected]. merits of applied and basic research. (quoted in Bromberg 1995).

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms Figure 1. Many of the elements that underlie a scientific discovery can be identified by tracing citations in published articles, but ideas also come from outside the realm of science. In the case of Karl Alex M?ller's work, as the authors will explain later in this article, a major motiva? tion was the scientist's feeling that the highly symmetrical crystal structure that proved essential to the discovery of high-temperature supercon? ductivity had the affective power of a mandala, the highly symmetrical visual symbol of the universe used in Hinduism and Buddhism as a guide to meditation. M?ller later chose the Dharmaraja mandala, above, to illustrate an introspective essay on his sources of inspiration.

All this changed practically overnight (La2Cu04 or lanthanum cuprate, measure the phenomenon had been in 1986, with the publication of a set of doped with a small amount of bari? available for decades. papers by Karl Alex M?ller and his for? um). Not only did it have a remark? The discovery became an academic mer student Johannes Georg Bednorz, ably high Tc?in the neighborhood of and popular sensation, especially after two investigators at the IBM Zurich Re? 30 Kelvin?it was relatively easy to Paul C. W. Chu's group at the Universi? search Laboratory in R?schlikon, Swit? prepare by techniques and to ty of Houston and Mao-Ken Wu's team zerland. Unlike most of the previously modify by chemical substitution. at the University of Alabama jointly an? discovered superconductors, the new Whereas ground-breaking discoveries nounced in February 1987 that they had compound was a ceramic, a mixed ox? often involve new technology, in this achieved superconductivity at about 90 ide of barium, lanthanum, and copper instance the means to create and to Kelvin with materials related to the

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms tures well above 200 Kelvin (the freez? ing point of water is 273.16 K). The opi? um addicts' blue haze has dissipated, and some physicists have even dared to hope again that room-temperature su? perconductors will eventually be found.

A First-Level Analysis The main outlines of this discovery are well known, but our interviews and correspondence with M?ller and Bed norz turned up essential details miss? ing from other accounts. Here we set forth an account of the discovery of the first high-temperature superconduc? tors as M?ller and Bednorz experi? enced it, with particular attention to the resources, either intellectual or ma? terial, on which the discovery depend? ed. Then, based on this narrative, we put forward a systematic analysis, a schema designed to help answer the more general question of what it takes to make a scientific advance. M?ller, who was born in Basel, Switzerland, in 1927, graduated from the Swiss Federal Institute of Technolo? gy (ETH) in Zurich in 1958. ETH was the home base of the physicist Wolf? gang Pauli, who continued to teach Figure 2. Superconductivity, the loss of electrical resistance in a material, was discovered by the Dutch physicist (right, shown with colleague G. J. Flim and there after winning the in their helium-liquefying apparatus in 1922). Onnes found that mercury becomes supercon? 1945. M?ller said of Pauli, "he formed ducting at 4.2 degrees Kelvin (above absolute zero). Until Karl Alex M?ller and Georg and impressed me." As we were to dis? Bednorz published papers in 1986 describing a material that becomes superconducting at 30 cover, the student had learned more Kelvin, the discovery of superconductivity appeared to have little practical use. Onnes is than physics from his teacher. By 1963, only one of a large number of scientific "ancestors" to M?ller and Bednorz. (Photograph M?ller had joined the research staff of courtesy of the Deutsches Museum, Munich.) the IBM Zurich Research Laboratory, and in 1972 he was put in charge of the Bednorz-M?ller compound, a tempera? peak in Darien, the physicists at the physics group there. In 1982 he was ture well within the range of the inex? meeting "look'd at each other with a promoted to IBM Fellow, becoming pensive coolant liquid nitrogen. Now wild surmise." Or as a reporter put it: one of a handful of distinguished sci? high-school students could demonstrate "One could have felt as if one were a entists who were free to work on any? the phenomenon. A climax of excite? part of a ceremonial gathering to affirm thing they pleased. He was to use that ment was reached at the so-called a new cult" (Kurana 1987a). opportunity well. "Woodstock of Physics," a panel discus? After the tumultuous emergence of Previously M?ller had worked for al? sion on high-temperature superconduc? high-temperature superconductivity? most 15 years on a series of problems in tivity held at the American Physical So? even President Ronald Reagan hailed condensed-matter physics, many of ciety's annual meeting on March 18, the "new age" of superconductivity as a which had links back to his doctoral re? 1987, in New York City. Roughly 3,500 welcome "revolution" having great search. His Ph.D. thesis, done under physicists crowded into the hotel where promise for new products?M?ller and Georg Busch at the ETH, was on the the meeting was held, some lingering Bednorz were awarded, with the maxi? identification of the electron paramag? so long after the session ended that they mum possible speed, the Nobel prize netic resonance lines of iron ions, a sub? had to be ejected from the rooms by the for physics for 1987. Their discovery un? ject quite unrelated to superconductivi? hotel staff at 6 a.m. (Schechter 1989; leashed the energies of dozens of teams, ty. But as it happened, the material in Khurana 1987a; Robinson 1987). and laboratories all over the world which the iron ions were present as im? Here was everything a physicist rushed to synthesize other potential ox? purities was the then recently synthe? could wish for: a new class of materials ide superconductors. Indeed, it did not sized oxide strontium titanate (SrTi03), with great potential for generating new take long for the critical temperature to and that fact, in a way nobody could theories and new technologies. Above be raised to 125 Kelvin, and to even have foreseen, would turn out to be all, the discoveries provided that most higher temperatures at high pressure. M?ller's first step toward research on rare and most desired moment, a Today the record stands at 164 Kelvin, high-temperature superconductivity. glimpse of vast unexplored scientific with isolated observations, often tran? Indeed, M?ller's use of strontium ti? territory. Like Cortez's men on the sient, being reported of critical tempera tanate was entirely accidental. Initial

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms ly, he had set out to map the paramag? trained in , -state that it took M?ller by surprise. Still, at netic resonance spectrum of impurities and physics. M?ller and the outset the two men spent a fruit? in tin. When that worked out poorly, Gr?nicher were supervising his Ph.D. less couple of years with nickel-based M?ller explained to us, he went "by thesis at the ETH; not surprisingly, oxides. Right up to its culmination, chance into Professor Heine Gr?nich Bednorz's first experimental work was their research was typically in the "lit? er's office," looking for crystals of other on the growth and characterization of tle science" style, meaning on a rela? materials. Gr?nicher offered M?ller strontium titanate. tively small budget. Bednorz later de? some samples, and among them was Bednorz was an ideal partner for scribed it as a stage on a "long and strontium titanate. M?ller. As Bednorz explained in their thorny path." Moreover, they worked It was a fateful moment. Not only joint Nobel lecture, he had become in? in self-imposed isolation. M?ller told did strontium titanate help M?ller to terested in superconductivity in 1978, us that they kept their early work com? get his doctorate, it led him to study when he was invited by the IBM pletely to themselves, not informing the crystallographic literature about Zurich laboratory to improve the su? even the IBM managers, in part be? the class of materials to which this perconductive properties of strontium cause superconductivity research was compound belongs and set him on a titanate single crystals. In this he quick? not then a popular subject with man? road whose destination would become ly succeeded by adding trace amounts agement. This decision, made possible apparent only years later. of niobium to the crystal. Yet the high? by M?ller's status as IBM Fellow, was When he was made an IBM Fellow est achievable Tc was still only 1.2 also taken so that if they failed, they in 1982, M?ller told us, he felt that Kelvin, so his IBM supervisor had lost could quietly give the project "a burial since he had passed the age of 50, it interest, and Bednorz had returned to in very restricted family circum? was time for an entirely new challenge. the institute to work on his thesis. stances, in order not to jeopardize Bed Perhaps he remembered the advice of But the seeds of fascination with the norz's career." an old supervisor, H. Thiemann, whose field had been sown, and when M?ller The breakthrough came when they byword had been: "One should look asked Bednorz in 1983 to join him in decided to look for superconductors for the extraordinary." In any case, the search for a new superconductor, among copper-containing oxides, a class M?ller chose extraordinary conductiv? Bednorz accepted with such alacrity of materials fundamentally different ity as his next challenge. At the time superconductivity was not a promising field of research. Not only had the incremental progress to? ward higher Tc apparently stalled, but IBM had abandoned the effort to pro? duce a computer using Josephson junc? tions?electronic devices made of su? perconducting materials that can switch states faster than devices made of semiconductors?despite the enor? mous investments the company had made in this project. M?ller was aware of all of this. In 1978 he had spent an 18-month leave at IBM's Thomas J. Watson Research Cen? ter in Yorktown Heights, New York. John Armstrong, the vice president in charge, wisely gave M?ller discretion to pursue any subject he wished while he was there. That encouraged him to look into the troubled field of super? conductivity, about which he then Figure 3. American Physical Society's 1987 knew very little. As he put it, he started March meeting, later named the Woodstock "from page one of Michael Tinkham's of Physics, was an impromptu crash course book," Introduction to Superconductivi? following the discovery of high-temperature ty. But thorough study turned up no superconductors. According to one account, theory that would lead beyond the the meeting was "an insane physics demon? usual materials to new substances and stration.... Suddenly, over three and a half higher critical temperatures. M?ller thousand physicists (with twice that many then "decided I just don't talk to the elbows) seemed hell-bent on proving that two bodies could occupy the same place at theoreticians. They just held me back." the same time." Awarded the Nobel prize After he returned to Zurich, M?ller later that year for the discovery were Karl continued to work on superconductiv? Alex M?ller (for left), 60, and his former stu? ity, first alone, and then from 1983 with dent Georg Bednorz, who was 37. (Top photo? Bednorz. Born in Neuenkirchen, Ger? graph courtesy of the American Institute of many, in 1950, Bednorz was highly Physics; lower photograph courtesy of IBM.)

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms ture superconductivity and that the Jahn-Teller effect has little to do with establishing superconductivity in the high-temperature superconductors. Yet because these theories were compo? nents in M?ller and Bednorz's motiva? tion, they merit a brief summary. :"^yv'i V ' ...-4 .u. According to the BCS theory, super? conductivity arises from the interaction of , or vibrations of the atomic lattice, and electrons. In most metals, phonons scatter individual electrons. Under certain conditions, however, the interaction between phonons and elec? trons causes some electrons to couple together to form what are called Coop? ?. '-IiilK^;';-': er pairs. At sufficiently low tempera? ?i^:;v..^:..\ ^?rV'A:--\"'f'> 0i25 A/cm2 ^^fe^^--v tures, these electrons move as a coher? r%^;:;-; v^-.:V?>SO A/cm* ..'vr -j^-V'*; ? - \ ent group through the solid. Because ^'^^?^ ,;* --''--'^^r^?SO'A/cm? . ;^?.^ ? thermally excited phonons are too weak to disrupt the entire group, the flow of electrons persists ^definitely, making the material a superconductor. M?ller and Bednorz expected oxides with mixed valence states to exhibit particularly strong electron- ^ ,vV^? 200 . 3?v:yf -' * - coupling. Barium-doped lanthanum cuprate met this criterion. They also thought a material that ex? Figure 4. Discovery of the first high-temperature superconductor, barium-doped lan? hibited a strong Jahn-Teller effect thanum cuprate, was published in Zeitschrift f?r Physik B, a journal read by few supercon? would be a good candidate. Some ductivity researchers. Although there was good evidence that the compound was supercon? are so constituted that as an elec? ducting, confirming measurements of magnetic susceptibility and the determination of the tron moves through them, positively Meissner effect had yet to be made. The crucial figure showed the temperature depen? charged ions (atomic nuclei with their dence of the resistivity of lanthanum cuprates doped with varying amounts of barium inner-shell electrons) markedly shift to? (Ba^La^CugOg^y)). (The two upper curves should be read against the left scale and the lower one against the right scale.) After initially increasing as the temperature was low? ward the electron, and negatively ered, resistivity suddenly plunged to zero. The figure's shock value, however, lay in its charged ions shift away from it. The abscissa: The materials underwent this transition at temperatures well above absolute electron is accompanied by a cloud of zero. (Reprinted with permission of Springer-Verlag.) phonons that result from this deforma? tion of the atomic lattice. Together the from those that had been ransacked by joint Nobel prize lecture, the team's electron and the phonons are called a the pioneers in the field, such as "aim was primarily to show that oxides , an entity whose effective mass Matthias. During a literature search Bed could do better in superconductivity depends on the displacement of the norz happened on a 1985 paper by than metals and alloys." ions. This mechanism appeared to al? Claude Michel, L. Er-Rakho and Bernard They had several reasons for strik? low for the persistence of the supercon? Raveau of the Universite de Caen that ing out in this new direction. Some ox? ducting state at higher temperatures, described barium-doped lanthanum ides, including strontium titanate, had whereas the normal BCS mechanism cuprate. But the authors were chemists previously been found to be supercon? implied that the superconducting state and had concentrated on catalytic rather ductors of the traditional sort, although would not, in general, persist at higher than superconducting properties. with T/s no higher than 14 Kelvin, temperatures. The decision to investigate the ox? they ranked well below the niobium M?ller had read a paper by Karl ides, which is a key turn in this story, compounds. As M?ller and Bednorz Heinz H?ck and H. Nickisch of the "took every condensed-matter physicist later noted, they were also reasoning Technische Hochschule in Darmstadt, by surprise" (Chakravarty 1994). Indeed from the then-standard theory for su? , and H. Thomas of the Uni? one physicist recently confessed to us perconductivity?the BCS theory, versit?t Basel in Switzerland (H?ck, that when he and his colleagues had named after physicists , Nickisch and Thomas 1983) that led heard M?ller "was searching for high and Robert Schrieffer? him to think that a material that met Tc in oxide, we thought he was crazy." and the Jahn-Teller theorem devised by the Jahn-Teller criterion and was metal? Up to that time searches had concen? physicists H. A. Jahn and Edward lic at high temperatures might have an trated on intermetallic compounds; ce? Teller. This is one of the interesting unusually high Tc. The lanthanum ramic oxides were generally thought to ironies of the story, because it is now cuprate met those criteria as well. be insulators, not conductors, much less thought that the BCS theory has only But, as M?ller told us, there was an? superconductors. But according to their limited applicability to high-tempera other crucial factor: the attraction that

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms he in particular felt toward that sub? stance because it had a -type structure. This structure had special meaning for M?ller; he said he had an "atavistic type of feeling that it might work for superconductivity." When he and Bednorz came to deliver their joint Nobel lecture, they gave it the signifi? cant title, "Perovskite-type Oxides? The New Approach to High-Tc Super? conductivity." Perovskites, named in 1830 in honor of the Russian amateur geologist Lev Aleksevitch von Perovski, are a class of that have a particular atomic arrangement. In their ideal form perovskites, which can be de? scribed by the general formula ABX3, consist of cubes that are decorated with three elements. The A cation ^^^^^ 111^^ (positively charged ion) lies at the cen? ter of each cube, the B cations occupy all eight corners and the X anions (negatively charged ions) lie at the midpoints of the cube's 12 edges. The cubic structure has particular appeal because, of the seven possible crystal systems, it is the one with the highest degree of symmetry. As we saw, M?ller and Bednorz had each devoted their graduate research largely to the perovskite strontium ti c d tanate. M?ller later wrote that "the per? ovskite structure determined, even Figure 5. M?ller decided to investigate the lanthanum cuprates in part because he thought they dominated, my scientific efforts for were perovskites, a class of ceramics characterized by a highly symmetrical crystal structure. A many years" (M?ller 1988). Indeed, in crystal can be described as a lattice, or space-filling construct, adhering to certain operations M?ller's extensive bibliography, per? that define the relations among points in the lattice. These operations include, for example, ovskites recur in widely varying stud? rotations about a point and reflections about a plane. Each of seven crystal systems?the cubic, ies, ranging from paramagnetic reso? tetragonal, orthorhombic, hexagonal, trigonal, monoclinic and triclinic?is defined by a set of nance to sound attenuation and heat symmetry elements. By analogy, the manner in which a crystal system exhibits a set of symme? capacity, from structural phase transi? try elements can be grasped by examining M. C. Escher's "Study for Regular Division of the tions to photochromism. For example, Plane with Angels and Devils," a two-dimensional space-filling construct. The pattern, which M?ller gave special attention to per? has twofold and fourfold rotational symmetry (a) and mirror symmetry (b,c), can be construct? ed by repetition of a square motif (d). ovskites in a decade-long investigation of the manner in which the Jahn-Teller effect can lead to structural phase tran? In M?ller's that their case reports the thematic were "met influence by a skepti? sitions (Thomas and M?ller 1972). on thecal scientificaudience" imagination (Bednorz was and just M?ller as As M?ller emphasized, perovskites compelling, 1987b). But as soonwe shall the confirmationssee. came "always worked" for him. This highly After pouring reading in, the and French research paper groups about grew symmetric structure became for him a barium-doped explosively lanthanumthe world over. cuprate, Bed thematic guide, quite different from and norz and M?ller prepared the com? supplementary to the elements tradi? pound A Second-Leveland showed that Analysis it became su? tionally considered central to the logic perconducting For a serious at astudy temperature of what of it about took to of scientific research. We recognize that 30 Kelvin, make thisa Tc discoverysubstantially and above what that lessons M?ller, in this tendency, joins many oth? of any it implies,previous wematerial. must Theypress alsoon beyondcon? er scientists who found themselves be? firmed this that sketch the ofsample events exhibited to a deeper anoth? level, ing led by thematic commitments, at er important where the indicator resources of superconduc?that history had least during the early, rather private tivity, prepared the Meissnerfor the success effect: of When the team a lie stages of their projects. Einstein, for ex? superconductor hidden. A complete in a magnetic analysis field wouldis ample, had a predilection for symme? cooled take to into the temperatureaccount in more at which detail it the try, continuity and classical causality, loses personal resistance, research all or trajectoriespart of the ofmag? M?ller whereas Heisenberg embraced disconti? netic and flux Bednorz, within the evaluate material the is expelled.influences nuity and abandoned classical causality. Still, of Bednorz encounters and M?ller with otherinitially researchers, found

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms Figure 6. Symmetries the (upper left) and lanthanum ^0/^ ^^^^^^^^ superconductors^jj^j (right) ^^^^^^^^ are often explained with polyhedral '"' models. ^^^^^^^B'' ^_ ^ ^^aaL ^^^^^^^H In an AB03 perovskite six oxygen atoms (blue spheres) surround the ^^^^^^^H^d??^^fc '^^/^^^?H^^^^^^^H B cations, which form an octahedron. A cations are shown in yellow, ^^^^^^^^^^^BHft^ WJjaSj^^^^^^^^^^H forming a network linked by green "bonds/' Lanthanum cuprate ^^^^^^^^^^^^^K. (La2Cu04) has similar structure, the octahedra ^^^^^^^^^^^^^^nttHfittHHBjjjj^^^^^^^^^^^^^H four rather than thus form Cu-O planes ^^^^^^^^^^^^^^^^^^I^^^^^^^^^^^^^^^^^^H enhance the for superconductivity. ^^^^^^^^^^^^HIHHHHIHH^^^^^^H^^^^^^H and thoroughly explore the education? tween scientific research efforts is that scientific and historical background al systems through which they passed, of adapting, assimilating, transform? knowledge to find implicit citations in as well as the universities and corpo? ing?or in general "borrowing"? the target paper or in the ancestral pa? rate institutions that employed them. whether consciously or not. pers. Finally any genealogical exercise Here we concentrate on the vast trea? Such borrowing leaves identifiable is open-ended; how far back to trace the sury of intellectual and material re? traces, just as one can discern one's an? connections is a pragmatic decision. We sources that these two scientists were cestors' traits in one's own makeup. To have found that it is not necessary to go able to exploit. On the basis of this case pursue this suggestive metaphor, it back farther than three or four "genera? history, we then generalize, proposing should in principle be possible to re? tions" to test interesting hypotheses a structured description of how new veal many "generations" of "ances? about scientific innovation. scientific work is rooted in and nour? tors" that lie behind a scientific work. A genealogical analysis of Bednorz ished by previous achievements, some In short, "influence" can be opera and M?ller's main scientific publica? from the distant past. tionalized by attempting to tease out tions announcing the discovery of It is often said that scientific work is the genealogy of a work by looking for high-temperature superconductivity "based on" earlier work, or that earlier documentable facts that are equivalent shows the need to distinguish among work "gave rise to" later work; there is to a line of inheritance. the various types of resources on also much talk of "traditions," "influ? One way to locate the resources that which the team drew. They made use ences" and "connections." These no? were used in a given piece of scientific of at least four sets of resources: initial, tions, we believe, must be made more work is to trace the citations to publica? motivating theoretical framework and precise to be useful. In particular, we tions or to private communications it ideas (schema); experimental tech? seek to operationalize them, that is, to contains. To be sure, citations cannot be niques and material resources (produc? define them in terms of identifiable used blindly, because they may be tion); means of gathering and analyz? and repeatable operations. merely pro forma, intended to acknowl? ing data (observation); and theoretical By resources we mean mathematical edge the existence of related projects in concepts for mteipreting the results (in? techniques, physical laws, analytical the same field, or to serve other, largely terpretation). Figure 7 indicates the instruments, factual information and social purposes. A second problem is kinds of items that make up these four the like. Although an investigator may that not all important resources are ex? main components. well create some such resources on the plicitly cited. Many resources will be Analysis of the original five papers spot, more frequently they are derived considered generally known and silent? that comprised the announcement of from previous work done by others. ly assumed. The scientific genealogist, their breakthrough (Figure 7) quickly Indeed the most important relation be therefore, must rely on his or her own reveals a number of silent resources

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms that M?ller and Bednorz put to use. ty: zero electrical resistance and the publication by Hugh L. Callendar of the For example, among the tools for ob? Meissner effect. Cavendish Laboratory in Cambridge servation were several standard tech? Figure 7 shows that each resource can that ushered in the resistance ther? niques no longer referred to explicitly be connected either to one of the two mometer as a practical means of mea? in research reports: x-ray powder dif? dozen publications explicitly referred to suring temperature. fraction for analyzing the structure of in the Bednorz-M?ller papers or to a It doesn't take long for the Bednorz the sample and various electrical resis? publication implicitly cited in their pa? M?ller work to reveal a broad and in? tance thermometers, among others. pers. For example, the passing reference tricate system of ancestors. Our search Similarly the theoretical resources to the Meissner effect implicitly refers revealed many cross references among needed to interpret the experimental to the 1933 publication describing the early resources and also quickly took results included some long considered effect by German physicists Walther us back to work done a century or commonplace and whose original Meissner and Robert Ochsenfeld. Simi? more ago. Unwittingly but docu? sources were not cited, such as the cri? larly, the platinum thermometers the mentary the stage for the 1986 discov? teria for identifying superconductivi teams used imply reference to an 1887 ery was set by scientists, many long in

schema -^iMte ' ? codde-hldh- -

production " _;_ ^_ ^_^^^^^ helium liquefler_ ^_flow cryostat_ obseiyatior^: :^_? ? ' ' ' '' _ x-mvpowderdfffractbn 'BBBBBiy^ ^ UpsephsQn Junctions-:'. ? ^^^^^^P ^^BBBB /" . ? ~ . ? , -j. platinum thermometers I ^^jP^'" ': ; oermanium^ I _\_zero resistance _j ^^^^ ?????_Meissner effect_||| ^^^^m ^^^M peroolativebehavior_|| ^^^M onset at resistivity peak_| ^^^^^^B Ferro! glass interpretation ^

Figure 7. To determine the immediate intellectual and material "ancestry" of the discovery of high-temperature superconductors, the authors traced implicit and explicit citations ("+" indicates additional coauthors) in five papers that can be regarded as the essential core of the Bednorz-M?ller work. This genealogical analysis quickly showed that at least four types of resources fed into the discovery of high-tempera? ture superconductivity: schema, the theoretical framework in which the scientists phrased their inquiry; production, the experimental tech? niques and material resources needed to produce the superconducting compound; observation, the means of gathering and analyzing data about the compound's properties; and interpretation, the theoretical concepts needed to interpret the data they obtained. Although intellectu? al primacy is often given to theory, the proper apparatus can play at least as important a role in scientific advances; all work with supercon? ductors, for example, was predicated on the development of the means to reach temperatures near absolute zero.

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This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms their graves. For instance, the appara? hannes Kepler in a book coauthored Borrowing of resources routinely takes tus commonly used to liquefy helium with psychoanalyst Carl Jung (Pauli place between different traditions within a today stems from a liquefier developed 1952). Much impressed by that essay conventionally defined discipline. For in? by the MIT engineer Samuel C. Collins M?ller started to read Kepler avidly thus stance, among the theoretical ancestors in 1947, whose predecessor was the encountering Kepler's deep commit? of the Bednorz-M?ller work are ideas Russian physicist Pyotr Kapitza's 1934 ment to the guidance of three-dimen? from thermodynamics, statistical me? liquefier, which in turn made use of sional stmctures of high symmetry?the chanics, the old quantum theory, two principles of cooling first laid out five Platonic solids?in his work on plan? quantum mechanics and quantum by British physicists William Thomson etary motion (Figure 10). field theory. Even when a given work (Lord Kelvin) and James P. Joule in the M?ller continued, "If you are famil? superficially appears tobe the result of a 1850s and by the French chemists iar with Jung's terminology the per? narrow line of research, it is likely to Nicolas Clement and Charles-Bernard ovskite structure was for me, and still have a deep and broad ancestry. When Desormes in 1819. is, a symbol of?it's a bit high scientists borrow from different sub Obviously, this network must be ex? fetched?but of holiness. It's a man fields, these can blend together or be tended to yet earlier generations (Fig? dala, a self-centric symbol which deter? transformed in an alchemical process ure 8). Moreover, if one focused on any mined me.... I dreamt about this that turns them into gold. One may also one node?say the BCS theory of perovskite symbol while getting my note that the unpredictable way scien superconductivity?it would reveal a Ph.D. And more interesting about this broad and intricate network of its own is also that this perovskite was not just (Figure 9). That, of course, is the point: sitting on a table, but was held in the In an operationally meaningful sense hand of , who was my we begin to perceive "what it took" to teacher." At the time, M?ller had di? discover high-temperature supercon? vulged this aspect of his inspiration ductivity. We can generalize that any only to friends and to Pauli's last assis? significant advance relies on a large but tant, Charles P. Enz. He has since dis? identifiable set of earlier contributions. cussed it in an introspective essay Some may be famous and profound, (M?ller 1988) illustrated with the Dhar many more are much less significant in maraja mandate (Figure 1). themselves. But all have served, almost To the historian this is familiar always unwittingly, to prepare for the ground. Scientists from Kepler to emergence of the new scientific or tech? Kekule, from Newton to Crick and Wat? nological achievement. son, were guided in the early stages of scientific research by a visually power? The Private Dimension ful, highly symmetric geometrical de? As we have noted, tracing the genealo? sign. In faithfulness to M?ller's self-re? gy of a scientific discovery through the port, our genealogy should include a published literature does not uncover new type of resource, "personal themat? every factor of relevance to it. Perhaps ic presuppositions," and with it a new the most intriguing needed addition is line of inheritance, reaching back first to the private dimension of scientific dis? Pauli and Jung and then to the works covery. Because of the tradition of for? of Johannes Kepler four centuries earli? mality in science writing, this aspect of er. This added intellectual resource discovery rarely survives in the pub? played as big a role in motivating the lished record. But we were lucky. 1986 discovery as any of the other re? When we asked M?ller to elaborate on sources we have mentioned. Other per? his remark that the perovskite struc? sonal thematic presuppositions of vari? ture "always worked" for him, he ous sorts are found to be essential obliged us by sharing in some detail an motivators in major advances through? aspect of his motivation that would or? out the history of science. dinarily be kept private. His unlikely choice of a perovskite in Some Testable Hypotheses his search for Wgft-temperature super? What can we learn about scientific dis? conductors was guided not just by the covery in general from this genealogi? force of (well-rewarded) habit As he put cal analysis of a particular advance? it: "I was always dragged back to this We offer four hypotheses that may be symbol." He first became fascinated found to hold generally for modern with this highly symmetrical stmcture in science. Although students of scientific Figure 8. More complete genealogical 1952, when he was working on his doc? discoveries will not find them surpris? analysis of the Bednorz-M?ller achieve? torate. Wolfgang Pauli, who as we have ing, we would contend that our ge? ment quickly uncovered a broad and deep mentioned was one of MuQer's profes? nealogical method of analysis has al? network of intellectual and material ances? sors at ETH, had just published an essay lowed these hypotheses to be put in a tors, grouped here generally as in Figure 7, on the influence of archetypal concep? more testable, and therefore more use? with schema resources at the top and inter? tions in the work of the astronomer Jo ful, form. pretive work at the bottom. For illustrative

372 American Scientist, Volume 84 This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms tdsts reach back to earlier research in a also found in theoretical ones, has, we SQUIDs, making possible exquisitely different part of the discipline suggests suggest, become more and more char? sensitive magnetic susceptometers, it would be futile to attempt to "ration? acteristic of modern scientific work. whose development is considered a alize" or "direct" this process but argues Basic research borrows resources from piece of applied work. The suscep? for making a scientific education as applied research, and applied research bor? tometers, however, proved useful in wide-ranging as possible. rows resources from basic research. A good further basic research into supercon? Borrowing of resources also routinely example of this symmetrical exchange ductivity, including Bednorz and occurs across traditional boundaries be? is Bednorz and M?ller 's use of a M?ller's. In short, to use a metaphor tween disciplines. The Bednorz-M?ller SQUID (superconducting quantum from physics, the exchange of energy work borrowed directly or indirectly interference device) to measure changes between pure and applied research re? from a wide variety of disciplines, each in magnetic fields. The initial pursuit of sembles the exchange of energy be? with its own professional societies and superconductivity can be regarded as tween a pair of coupled pendulums. journals. They included physical chem? basic, or ''arriosity-driven/' So can Bri? Such feedback effects can be observed istry, material science, crystallography, an Josephson's prediction that super? even within discipline-oriented re? metallurgy, electronics and low-tem? conducting currents can tunnel across search lines. perature techniques. This feature, most an insulating film. But then the Joseph Our findings emphasize the great impor? obvious in experimental projects but son effect led to the production of tance for scientific research of unintended

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purposes, the first-generation ancestors (red fines) are shown in more detail than earlier generations (green lines). The genealogical tree has been arbitrarily truncated; each generation, of course, has its own ancestors. Even without the ability to indicate every traceable "ances? tor/' the figure embodies the central argument of this article, namely that every scientific advance depends on many previous advances in a variety of unrelated disciplines. Likewise resources interconnect: Observation leads to new theory and vice versa. Schemes for directing funds solely to "strategic" research areas ignore the dense interconnectedness of the scientific enterprise. Note that the horizontal scale is compressed as one passes into the 19th century (facing page). Also, some important work in this field is absent in this representative sketch of the authors' genealogical tracing because of lack of space, or because M?ller and Bednorz did not refer to it.

This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC 1996 July-August 373 All use subject to https://about.jstor.org/terms has transpired in the continued absence of any consensus about the mechanism of high-temperature superconductivity. The M?ller-Bednorz story, replete with unpredictable turns of events and rife with unintentionality, has yet another twist. As we noted, the perovskite struc? ture inspired M?ller and Bednorz to gamble on investigating the oxides in the first place. Their barium cuprate com? pound contained well-separated planes of copper and oxygen atoms, and these layers turned out to be a universal prop? erty of high-temperature superconduc? tors. Moreover, these layers exist because the compound is not, after all, a true per? ovskite; because of the way its unit cells stack, it has orthorhombic rather than cu? bic syrrimetry (see Figure 6). As M?ller said to us in this connection, although Kepler tried to decompose planetary or? bits into perfect circles, he was led to el? lipses instead?but thereby helped pre? pare for Newton's Principia.

Unity in Science If the four hypotheses we developed are ^-^?^^^1 more generally confirmed, they will have the effect of providing support for m^-v-?HH^^i the old assumption that there is some underlying unity in science, perhaps not of the Theory-of-Eveiything variety but Figure 9. Density of connections that characterizes genealogical analysis of scientific work is of a different, operational kind. demonstrated by focusing on one node in Figure 8?the BCS theory for low-temperature superconductivity?which explodes to reveal its own dense network of A ancestors. distinguished This fig? and vocal minority of ure also illustrates a quixotic aspect of scientific discovery: The BCS scientiststheory in (includingits original Philip W. Anderson, form is now widely thought not to apply to high-temperature superconductors, who won buta Nobel ideas doprize for his work on not have to be correct to be fruitful. the theory of superconductivity) has as? serted that we should not look for unify? interactions or applications. Most ing theories bor? emerging from the study of rowed resources had been developedelementary particles, and that each area by others in research with a goalof science, quite such as biology or fluid dy? different from that of the eventual namics, bor? has its own laws, which cannot rower. Moreover, the research be ofderived the from something more funda? borrower also often ends upmental. some? Those arguments, whether right where other than the intended or destina? wrong, do not touch our idea of unity, tion; for example, Onnes's initial which dis? is exemplified in the ceaseless bor? covery of superconductivity wasrowing based connecting diverse traditions on ideas of Kelvin's, which predicted and disciplines. In principle, any two re? "exactly the opposite of what search was efforts, however removed in time, found eventually" (Meijer 1994). subject As we or purpose, may turn out to be have noted, Bednorz and M?ller genealogically dis? connected. And in the covered high-temperature supercon? limit, the whole of natural science may ductivity by studying a compound be represented that as one thickly linked con? had been synthesized and researched tinuum, which can be divided into dis? by others for unrelated purposes. tinct Nordisciplines and traditions only in a Figure 10. Like many scientists, M?ller could wasthe team have predicted morethat now, or less arbitrary way. However also influenced by older scientific ideas. a decade after their discovery, theythere may are differ, the multitudinous pro? Wolfgang Pauli, his teacher, had written an over a hundred high-temperature jects ofsu? science share in and emerge from essay on archetypal conceptions in the work of Johannes Kepler, including aperconductors model of as well as a growing a common set history. the planetary orbits as a concentric of structure industrially promising applications^? defined by the enclosed highly symmetrical motors, transformers, thin filmsImplications and for Science Policy solids. (Reproduced from Kepler, powerMysterium cables?some of them already This study on has significant implications for Cosmographicum, 1596.) a production basis. Moreover, all science of this policy. It suggests, first of all, that

374 American Scientist, Volume 84

This content downloaded from 140.247.137.37 on Mon, 29 Jul 2019 20:22:04 UTC All use subject to https://about.jstor.org/terms far more attention should be paid to the But above all, our research suggests Bromberg, J. L. 1995. Experiment vis-a-vis the? history of actual advances. They demon? that the current debate about the rela? ory in superconductivity research: the case of Bernd Matthias. In Physics, Philosophy and strate, in operational terms, that major ac? tive merits of and support warranted the Scientific Community, ed. K. Gavroglu et complishments in science depend on for basic and mission-oriented research ah Boston: Kluwer Academic Publishers. healthy systems of education and re? is oversimplified. Historical study of Chakravarty, S. 1994. Cuprate superconduc? search administration that nurture a mix? cases of successful modern research has tors: A broken symmetry in search of a ture of basic, applied and instrument-ori? repeatedly shown that the interplay be? mechanism. Science 266 (21 October): 386-387. ented developments. The traditions and tween initially unrelated basic knowl? management styles of laboratories and edge, technology and products is so in? Dahl, P. F. 1992. Superconductivity: Its Historical their parent institutions can greatly ad? tense that, far from being separate and Roots and Development. New York: American Institute of Physics. vance or hinder research. At the Zurich distinct, they are all portions of a sin? laboratory M?ller and Bednorz benefited gle, tightly woven fabric (Mort 1994; Ehrenreich, H. 1995. Strategic curiosity: Semi? Ehrenreich 1995). Even research that conductor physics in the 1950s. Physics To? from access to highly trained machine day 48(l):28-34. and glassblowing techrricians, schooled in narrowly targets a specific application Felt, Uv and H. Nowotny. 1992. Striking gold in the traditions of excellence and crafts? sooner or later must rely on results from the 1990s: The discovery of high-tempera? manship that can be traced back to the a wide spectrum of research areas. Thus ture superconductivity and its impact on guilds of previous centuries. Then too, it it is still sometimes said that Irving the science system. Science, Technology & Hu? man Values 17:506-531. was probably not an accident that their Langmuir looked into blackened light discovery, which is basically an advance bulbs and so created modern surface H?ck, K-Hv H. Nickisch and H. Thomas. 1983. in the science of materials, occurred at a chemistry. But of course his achieve? Jahn-Teller effect in itinerant electron sys? tems: the Jahn-Teller polaron. Helvetica Phys laboratory with a long-standing commit? ment did not spring full-fledged from ica Acta 56:237-243. ment to this science, most notably to the his brow. Its genealogy, if traced back as Khurana, A. 1987a. Superconductivity seen study of ferroelectricity. carefully as we have traced the geneal? above the boiling point of nitrogen. Physics But the most striking feature of the ogy of Bednorz and M?ller's discovery, Today 40 (4):17-23. culture at the Zurich laboratory was the would quickly reveal the crucial role of Khurana, A. 1987b. Bednorz and M?ller win willingness to give good people the free? many types of research in earlier gener? Nobel prize for new superconducting mate? dom to pursue projects with long gesta? ations. If we wish to achieve notewor? rials. Physics Today 40 (12):17-19. tion periods. This was rewarded twice in thy science, even if noteworthy is de? Matricon, J., and G. Waysand. 1994. La Guerre quick succession. The year before Bed? fined to mean only science with an du Froid: Une Historie de la Supraconductivite. norz and M?ller won the Nobel prize in economic payoff, the nation has no al? Paris: Editions du Seuil. physics, it had been awarded to Gerd ternative but to support the seamless Mort, J. 1994. Xerography: A study in innova? Binnig and , also of the web of research. tion and economic competitiveness. Physics Zurich laboratory, for their patient devel? Today 47(4):32-38. opment of the scanning tunneling micro? Acknowledgments Meijer, P. H. E. 1994. Kammerlingh Onnes and scope. The stories of the transistor and We gladly acknowledge advice on early the discovery of superconductivity. Ameri? can Journal of Physics 62:1105. the laser also suggest that the chance of drafts received from }. Georg Bednorz, M?ller, K.A. 1988. ?ussere und innere serendipitous encounters with key ideas George Benedek, Henry Ehrenreich, Theodore H. Geballe, Marc A. Kastner, K. Forschungserfahrung und Erwartung. Tech? is increased by permitting research to nische Rundschau (44):2^. proceed at an unforced pace. Alex M?ller and Michael Tinkham. One of M?ller, K. A., and J. G. Bednorz. 1987a. The We recognize here the well-known us (Holton) is also grateful for support of discovery of a class of high-temperature su? phenomenon of the self-amplification this study from the Andrew W. Mellon perconductors. Science 237:113. Foundation. of self-confident, successful, high-qual? M?ller, K. A., M. Takashige and J. G. Bednorz. ity cultures. They exhibit what Robert 1987. Flux trapping and superconductive K. Merton of Columbia University, Bibliography glass state in La2Cu04_ Ba. Physical Review Letters 58:1143-1146. who pioneered the modern sociology Bednorz, J. G., and K. A. M?ller. 1986. Possible of science, has memorably termed the high Tc superconductivity in the Ba-La-Cu-O Pauli, W. 1952. Der Einfluss archetypischer Matthew Effect (a reference to the text: system. Zeitschrift f?r Physik B 64:189-193. Vorstellungen auf die Bildung naturwis? Bednorz, J. G., and K. A. M?ller. 1987a. A road to? senschaftlicher Theorien bei Kepler. In Na? "Unto every one that hath shall be giv? en, and he shall have abundance..." wards high Tc superconductivity. Japanese turerkl?rung und Psyche, C. G. Jung and W. Journal of Applied Physics 26 (Supplement 26 Pauli. Zurich: Rascher Verlag. (Translated Matthew 25:29). 3):1781-1782. into English by R. F. C. Hull and P. Silz as It is equally important that the sys? Bednorz, J. G., and K. A. M?ller. 1987b. Perovskite The Interpretation of Nature and the Psyche, tem of research administration encour? type oxides?the new approach to high-Tc su? published in 1955 by Pantheon Books.) age the flexibility that promotes bor? perconductivity (Nobel lecture). In Les Prix No? Robinson, A. L. 1987. Research news. Science bel 1987. Stockholm: Almqvist & Wiksell 235:1571. rowing within and across disciplines International, pp. 65-98. (Also printed in Re? Schechter, Bruce. 1989. The Path of No Resis? and between basic and applied re? views of Modern Physics, 1988,60:585-600.) tance: The Story of the Revolution in Supercon? search. The culture of the laboratory, in? Bednorz, J. G., M. Takashige and K. A. M?ller. ductivity. New York: Simon and Schuster. cluding its financing, should allow both 1987a. Susceptibility measurements support a natural, unforced pace of work and a high-Tc superconductivity in the Ba-La-Cu-O Thomas, H., and K. A. M?ller. 1972. Theory of system. Europhysics Letters 3:379-386. a structural induced by the degree of self-direction that allows re? Jahn-Teller effect. Physical Review Letters searchers to draw on the personal Bednorz, J. G., M. Takashige and K. A. 28:820-823. M?ller. 1987b. Preparation and characteri? sources of inspiration on which admin? zation of alkaline-earth substituted super? Tinkham, Michael. 1975. Introduction to Super? istrative rule books and traditional sci? conducting La2Cu04. Materials Research conductivity. New York: McGraw Hill. Sec? ence texts are so silent. Bulletin 22:819-827. ond edition 1996.

1996 July-August 375

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