True Genius: The Life and Science of John Bardeen: The Only Winner of Two Nobel Prizes in Physics (2002)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

15 Pins and Needles and Waves And this gray spirit yearning in desire To follow knowledge like a sinking star, Beyond the utmost bound of human thought. ... Old age hath yet his honour and his toil; Death closes all: but something ere the end, Some work of noble note, may yet be done, Not unbecoming men that strove with Gods. ... Tho’ much is taken, much abides; and tho’ We are not now that strength which in old days Moved earth and heaven; that which we are, we are; One equal temper of heroic hearts, Made weak by time and fate, but strong in will To strive, to seek, to find, and not to yield. —Alfred, Lord Tennyson, “Ulysses” M ost physicists accept aging as the ultimate obstacle in research. As their mental agility and speed decline, they shift their efforts to ancillary work, such as teaching or administration. Some change fields. But the few who produce works of genius often try to buck the trend. Expecting their passion and experience to compensate for their aging, they strive to achieve 284 

Pins and Needles and Waves 285 yet one more great work. In this respect Bardeen was typical of the exceptionally creative. In the 1980s, when Bardeen was in his seventies, his research fo- cused on developing a theory to explain an ordered conduction phe- nomenon involving charge density waves (CDWs). Several research groups had observed these unusual waves in the early 1970s. The periodic modulations of the electron density and the positions of the lattice atoms occur at low temperatures in certain materials having a quasi-one-dimensional structure—the conduction pro- ceeds inside them along linear chains that hardly interact with one another. One of the experimentalists working in the field of CDWs was George Grüner at the University of California at Los Angeles (UCLA). Grüner aptly compared the electron density in CDW ma- terials to “the ranks of a marching band.” In a 1994 Scientific American article coauthored with Stuart Brown, he explained that when there is no voltage the marchers (electrons) stand still. But if a voltage is applied, a new phenomenon occurs above a certain thresh- old: “the band begins to march” with a definite periodicity that differs from that of the crystal lattice. The large current that forms is nonlinear with the voltage; increases of current are not propor- tional to increases of voltage, as they are in ordinary conductors. The ground state is no longer static, but takes the form of a sliding wave. In the early days of the quantum theory of solids, Rudolf Peierls had raised the possibility of creating charge density waves. On purely theoretical grounds, he noted in 1930 that the one-dimensional metal (the linear chain) is mathematically unstable. He demon- strated what became known as the “Peierls instability”: when the electron density distorts to form a wave tied to a periodic distor- tion of the underlying crystal lattice, the energy of the system is lowered. This result suggested that charge density waves might exist in nature, but the waves could not be observed until forty years later when experiments were performed in compounds approximating a one-dimensional metal. Well before that, in the early 1950s, Bardeen had suspected that CDWs are somehow related to superconductivity. In those years he developed a theory based on the assumption that the CDWs are the 

286 TRUE GENIUS mechanism for superconductivity. Unfortunately, the theory worked only in one dimension, and the predicted size of the energy gap did not fit with experimental findings. Still, he continued to believe that the CDWs and superconductivity could somehow be explained in a common theoretical framework. Both are collective states of matter that result from a broken symmetry. In CDWs the symmetry is “translational,” that is, the lattice is initially spatially uniform, whereas in superconductors the symmetry is a more mathematical one associated with conservation of particles. In both, the interaction of electrons with the lattice creates an insta- bility that causes energy gaps to form. And both are separated from the normal state by a second-order phase transition (known in the CDW case as the “Peierls transition”). Of particular interest to Bardeen was the fact that defects, or impurities added to the crystal, can “pin” (hold in place) the phase of the charge density waves to the lattice and that the phase can be “depinned” by applying a strong enough electric field. In 1976, Nai-Phuan Ong and Pierre Monceau in Berkeley dem- onstrated such pinning and depinning in a classic experimental study involving charge density waves created in the inorganic lin- ear chain compound NbSe3. Bardeen immediately recognized that explaining this phenomenon was a fertile problem. Here was an- other system to which Fritz London’s picture of long-range ordering could apply. Bardeen sensed intuitively that the CDW state is a macroscopic quantum phenomenon, analogous to super- conductivity but occurring in a different class of solids. The problem had the added attraction that CDW materials had properties—such as large dielectric constants and nonlinear current-voltage charac- teristics—of great potential importance to industry. The pinning and depinning can be imagined in nonquantum- mechanical (classical) terms by assuming the wave resembles a flat solid having a rough surface, like a washboard or sheet of corru- gated rubber in whose physical irregularities a defect could be caught. Bardeen’s picture of this pinning and depinning process as a quantum-mechanical phenomenon occurring on a macroscopic scale was analogous to Josephson tunneling of condensed electron pairs in a superconductor. Bardeen envisioned a collective tunnel- ing of condensed CDW electrons through a small pinning potential created by the impurities or defects of the material. “If you have a brick wall,” explained Grüner, “and you drive 

Pins and Needles and Waves 287 the car into the brick wall, you are more or less sure that you are not going to go through the brick wall to the other side intact.” In quantum mechanics this process, known as “tunneling,” has a finite probability. The CDW case can be imagined as a sort of gen- eralized Josephson tunneling phenomenon. If one has “say a row of soldiers, a million electrons,” the question becomes, “Can they somehow tunnel collectively at the same time?” Bardeen felt sure that it was possible as a consequence of the macroscopic quantum state. “It’s a beautiful concept,” said Grüner. “And it’s something that’s revolutionary, new, and has consequences.” These were powerful motivations for studying CDWs. According to Grüner, had Bardeen’s theory been validated, “without question it would have been a Nobel Prize, a third one.” Data from the early a.c. frequency experiments yielded an exponential dependence of electric field on frequency (a hallmark of tunneling) that could be fitted to Bardeen’s quantum-mechanical theory. Applying photon-assisted tunneling theory (PAT), in which absorbed quanta can bring electrons into a state in which tunneling is more likely, Bardeen described his pinning as “weak,” because the applied electric field did not need to be very strong. Initially, the many-body community was intrigued by Bardeen’s beautiful theory, but with time more physicists preferred the so- called classical model of an overdamped oscillator motion in a periodic potential. Among the prominent physicists who came to support the classical picture were Grüner, Patrick Lee, T. Maurice Rice, Philip Anderson, Alfred Zawadowski, and Paul M. Chaikin. This opposing model allowed for a quantum-mechanical response to the electric field, but with a considerably larger classical effect. It predicted measurable relationships between the amount of impurities present in the materials and the threshold voltage at which the CDWs would begin to slide. For a number of years, the classical and quantum-mechanical pictures would coexist. In 1980, while pondering his quantum-mechanical model for the charge density waves, Bardeen recalled the conversation in 1974 in which he had learned about the PAT theory. He had been speak- ing with John Tucker, a physicist then working at the Aerospace Corporation in El Segundo, California, near Los Angeles. Bardeen was visiting there at the invitation of Ivan Getting, his old friend from the Harvard Society of Fellows, who was now president of the corporation. During the visit, Tucker told Bardeen that he was apply- 

288 TRUE GENIUS ing photon-assisted tunneling theory to metal–superconductor tunnel junctions. Later used in the design of astronomical quan- tum receivers, such junctions could be set up at the interface between two superconductors, so that one electron could tunnel each time a photon was absorbed. One day in the spring of 1980, the telephone rang in Tucker’s office at the NASA Goddard Space Institute in New York City. Tucker heard a soft, raspy voice say, “Hello, this is John Bardeen.” At first he thought it was a prank. Bardeen told Tucker that he thought charge density waves were a macroscopic quantum phe- nomenon. He explained why he suspected that PAT might help to explain their transport. “He was very excited because if this were true, you’d see quantum phenomena in a regime that no one had thought possible.” Tucker was intrigued. “It was only the second example, besides superconductors, where you conduct electricity with a moving quantum ground state. There are other quantum ground states where all of the particles like to get in the same quantum state, such as superfluid liquid helium, but then it doesn’t carry a charge.” He was also aware that collaborating with Bardeen at this stage would be a gamble. At seventy-two the double Nobel laureate had passed the age at which most physicists contribute to cutting-edge research. On the other hand, if Bardeen’s idea were correct, it would be an extraordinary piece of physics. Bardeen was “reaching for something that was exotic, but not wildly implausible. Things that strange had happened before in physics.” The work could poten- tially open an “entirely new realm of quantum physics.” Tucker accepted Bardeen’s invitation to come to Urbana in the fall of 1981. Bardeen arranged that Tucker be named an untenured associate professor of electrical engineering, with the possibility of tenure after a few years. The offer also included funds to establish a research laboratory and to support a graduate student. Tucker’s first student would be John Miller. For a few years, Bardeen and Tucker’s work attracted favorable attention from the CDW community, which grew rapidly in the 1980s as its members looked ahead to wide use of CDWs in study- ing chaos and turbulence and in building amplifiers. As in earlier collaborative projects, Bardeen modeled the CDW collaboration on the family. He was the patriarch; Tucker was the adopted son. Jane often invited Tucker and his students to dinner, or to cook for them- 

Pins and Needles and Waves 289 selves, at the Bardeen home. “We used to hold group meetings over there,” Tucker recalled. “And every once in a while we’d cook burgers.” Usually they would meet in the large sunroom in the back of the house. “It had the kind of benches that you sit on, but they had drawers underneath.” On one occasion, a student opened a drawer and found two Nobel certificates bound in leather. “I said, ‘Gee John, you have a better class of junk in your drawers than I do.’ Everyone laughed, and he was sort of sitting there kind of scowling, like ‘What’s so funny?’” “Throwing theoretical spaghetti at the wall to see what sticks” was how Tucker characterized his early research with Bardeen. The team fitted a rudimentary tunneling hypothesis to the data. Then they adjusted their theory in stages. Miller and other students per- formed “mixing experiments” on CDWs by injecting signals of different frequency into a sample, holding the direct-current (d.c.) field below the threshold for depinning and adding an alternating- current (a.c.) field of gradually increasing frequency or strength. According to their theory, the tunneling would begin at a specific frequency and exhibit a characteristic dependence on the strength of the a.c. field. When their experiments failed, Bardeen shrugged off his disappointment, muttering, “I guess the system is still noisy.” “Maybe he was just carried away a little by how beautiful this could be,” Grüner said. “I think that deep down he thought that there is just one missing link, and that maybe everything is going to fall into place. In superconductivity there was just one missing link for half a century, which was the pairs, and then everything fell into place.” Myron Salamon occasionally dropped by Tucker’s lab. Salamon was then director of the National Science Foundation (NSF) pro- gram at Illinois’ Materials Research Laboratory, which was sup- porting the CDW work that Bardeen and Tucker were doing. Salamon grew worried when Tucker told him, “I’m really working hard to try to prove John is right.” Salamon cautioned, “That’s really not the attitude for an experimentalist—you measure what’s there and if the theory’s right, it’s right, and if it’s wrong you’re even happier because you’ve got something new.” Bardeen’s and Tucker’s network of associations with CDW experimenters included Grüner, who recalled, “The first set of experiments that we did really fitted.” Bardeen, Tucker, and Grüner 

290 TRUE GENIUS were able to demonstrate that the frequency dependence and volt- age dependence had the same functional form. They therefore felt that they had “strong supporting evidence for the photon assisted tunneling theory.” Experiments in Vienna by Karlheinz Seeger, an- other collaborator in the CDW work who had been a postdoc at Illinois in the 1950s also initially appeared to fit Bardeen’s theory. But such fits could also be made to the classical theory. To differen- tiate between the classical and quantum-mechanical hypotheses, they needed to demonstrate a threshold energy that depended upon the absorption of photons. They could not find it. Little by little, Bardeen and Tucker’s theory lost ground. The Bardeen-Tucker theory had fallen seriously behind the classical one by the time of the major CDW conference held in Budapest in early September 1984. At that meeting, Daniel Fisher and Leigh Sneddon of Bell Labs presented their case for the opposing classical model. But the CDW controversy was overshadowed by a tragedy that deeply touched both camps. Three days before the meeting, William McMillan, Bardeen’s former student and now colleague, was fatally hit by a car as he was bicycling on a country road near the town of St. Joseph, Illinois, not far from Urbana. Bill’s widow, Joyce McMillan, a crystallogra- pher at the University of Illinois, said her husband had preferred running to bicycling but had injured his knees. At the time of the accident he was bicycling because he needed new running shoes and “didn’t have one minute” to shop for them. At forty-eight, McMillan was in his prime. “He was building computers and run- ning computers twenty-four hours a day in his basement.” By the time he declined his invitation to the Budapest meeting, his main interest had shifted to spin glasses, the problem he was modeling on the computer he had built in his basement. After McMillan’s death Joyce realized he had been working on twelve papers at the same time, all published in the months before and after his death. Shocked to learn of the accident, Bardeen immediately sent a condolence telegram to Joyce from Budapest, explaining that there would be a time devoted to McMillan at the conference. “I feel a deep sense of personal loss of a former student and close associate on the staff of the physics department at the University of Illinois,” he said at the opening session. He requested a moment of silence. He also arranged that the conference proceedings be dedicated to McMillan. The department subsequently established the William 

Pins and Needles and Waves 291 L. McMillan Award, given annually to recognize outstanding con- tributions to solid-state physics by young researchers within four years of the receipt of their doctorates. Bardeen wrote a short biography of McMillan for the flyers distributed at the award presentation. Bell Labs continued to raise sharp objections to Bardeen’s quantum-mechanical theory. Despite harsh review of the NSF proposals and research papers that Bardeen and Tucker coauthored, Bardeen held fast to his belief that “excellent agreement is found between theory and experiment.” Several younger members of the group surrounding Philip Anderson talked and joked while Bardeen spoke at physics meet- ings. Tucker recalled that it “greatly upset Bardeen that people at Bell Labs would be calling him crazy and stupid in public, and openly laughing at him.” He had never before experienced dis- respect from the younger generation. In the fall of 1984 Joseph Lyding, a new assistant professor in electrical engineering, joined the Bardeen and Tucker team as an experimentalist. Lyding came to Illinois because of “the opportu- nity to work with someone like John Bardeen. That’s a once in a lifetime opportunity.” He began to grow high-quality crystals for the CDW experiments. The team had been getting most of their crystals from Grüner. By placing a thermal gradient across the crystals and measuring the effect on narrow band noise. “I could see the frequencies of the narrow band noise peaks shift and split into multiple peaks. It was a nice experiment.” Lyding recalled that it was “really nice working with Bardeen— he was so accessible.” When he wrote up his first paper and gave it to Bardeen, “it came back the next day with all sorts of interesting suggestions and comments. It was very positive.” Lyding also appreciated Bardeen’s frequent visits to the Electrical Engineering Research Laboratory (EERL), at least once or twice a week. “He’d come over to EERL and he would always talk to my students, and John’s students. He was very accessible and he never put himself above anybody, which is amazing, all things considered.” In the larger many-body world, however, the physics emerging from the collaboration was not faring well. Bardeen’s opponents accused him of blindly censoring their classical theory, rather than responding to its details. As their tone grew harsher, Bardeen’s patience wore thin. He returned some of the insults. At times he 

292 TRUE GENIUS accused his opponents of supporting the classical theory simply because it was easier to program on computers, tools of the new generation that he himself did not use. It had never been easy for Bardeen to discard a theory in which he had invested much time and energy, but in his younger years he would do so when necessary. Back then there had been more time left, making it easier to switch commitments. Now, in his late seventies, solving the difficult problems of explaining CDWs was a race against time. Reluctant to upset him, Bardeen’s friends avoided discussing CDWs in his presence. Family members encouraged him to work on his memoirs. He would not. Ignoring the problem was not an option for him, or for Tucker, who pushed Bardeen to be more com- plete in his explanations. The mood in Tucker’s lab grew tense. “Tucker always seemed on edge,” said Fred Lamb, who occasionally stopped by the lab. “And Bardeen would always be scowling.” In February 1987 Douglas Scalapino chatted with Bardeen at a conference. “You know, Doug,” Bardeen mused, “the establishment’s against me.” To Scalapino, “it sounded so incongruous that I couldn’t help but reply, ‘But, John, you are the establishment.’” Bardeen “smiled gently as he sometimes did, and we went on talking.” Bardeen’s health was noticeably failing. The macular degenera- tion that impaired his vision was an enormous hindrance to his work. It was not helped much by surgery. His frustration some- times overwhelmed him. Even playing golf was becoming difficult because of his vision loss and the gout in his legs. By early 1987, Tucker had to admit to his own serious reserva- tions about Bardeen’s theory, particularly its notion of weak pinning. He worried about Bardeen’s inability to justify the tunnel- ing expression behind the current-voltage curve. Could the Bell Labs theorists be right? Could the a.c. response of the CDWs be explained as a capacitor effect? Tucker told Lyding about a Bell Labs experiment that disproved Bardeen’s tunneling model and “said he actually woke up in the middle of the night realizing that what they’d seen was just some manifestation of this narrow-band noise. He could see his ticket to Stockholm had been ripped in half.” Bardeen and Tucker weathered a storm in the spring of 1987 when Tucker wrote a research proposal that did not oppose the 

Pins and Needles and Waves 293 classical model but took an open view. He was trying to reflect his own understanding of the problem and also avoid irritating the opponents. Several of them would surely be called in as reviewers. Outraged, Bardeen refused to sign until Tucker had inserted several sentences favoring the quantum viewpoint. The escalating tension between Tucker and Bardeen concerned Salamon, who worried that their lab had become a poor environment for students. Just then a new wave of excitement shook the physics commu- nity. In late 1987, J. Georg Bednorz and K. Alexander Müller, in Zürich, announced the discovery of a class of ceramics, perovskites that become superconducting at 35 K, a much higher temperature than predicted by the BCS theory. Potential applications boggled the mind. They included magnetic imaging, particle accelerator magnets, electrical generators, and magnetically levitated trains. The superconducting behavior of the perovskites was unexpected because BCS assumed that only metals and alloys could become superconducting. Bardeen and other theorists tried to apply the BCS theory, especially the notion of the Cooper pairs, to the new phenomenon of high-temperature superconductivity. Most were convinced that modifications to the theory would be needed to explain what became known as “high-Tc.” As interest shifted from CDWs to high-Tc, some of the tension around Bardeen relaxed. “All of us were quite excited when high-Tc came out and started working on it immediately, Bardeen among us,” recalled Salamon. At the huge “Woodstock of Physics” meet- ing on high-Tc, held in March 1987 at the New York Hilton, thousands of physicists packed into a huge ballroom to consider the implications of the new kind of superconductivity. Brian Pippard called it a “lemming effect.” “What we found when we took our first data on high heat ca- pacity was that some of the numbers that were being published by Bell Labs didn’t hang together,” said Salamon. In an effort to input all the data and compare what was known, he started putting to- gether “a spreadsheet with all of the BCS formulas.” Someone at lunch mentioned that “John is trying to do just the same thing; you ought to show it to him.” So Salamon took his spreadsheet over to Bardeen, who he found working quietly in his office. “He had his blackboard covered from edge to edge with formulas and expressions and calculations, and he had a little six inch slide ruler he was working with.” The numbers did not seem 

294 TRUE GENIUS to agree in places, so the two “sat down together, me with my spreadsheet computer output, and he with his things on the black- board, and checked each other’s numbers. And the end result was that we agreed on these.” Bardeen, “like the rest of us, was trying to figure out how much of the original BCS picture was valid and was going to stay together and how much new was needed.” Ever since the discovery of BCS, Bardeen had been eager to find new mechanisms for superconductivity. He “wasn’t at all wedded to the phonon mechanism as being the sole means of doing this.” Working together, Salamon and Bardeen became convinced “that the pairing picture was robust and that there may be other attrac- tive interactions that could be at work, but that all of the formulas in the BCS, the pairing mechanism, the opening of the gap, were all going to be robust.” In June 1987 they submitted a coauthored ar- ticle on the work to Physical Review Letters. “Boy I’m glad this high-Tc came out,” Salamon recalled think- ing, “because it will take John’s mind off this big fight he’s having with Tucker about the charged density waves.” The discovery of high-Tc did “put an end to that fight, or at least the open part.” When the NSF granted $350,000 extra to the Materials Research Lab to begin a high-Tc initiative, almost “everybody who was work- ing on these charge-density waves said, ‘I want to work on high-Tc anyway.’” Behind the scenes, Bardeen grew angrier by the day about the opposition to his CDW theory. He could not understand the resis- tance and took every opportunity to express his irritation. In May 1987 he wrote to H. Takeyama and H. Matsukawa, “It is inconceiv- able to me why people do numerical calculations on unrealistic and vastly over-simplified classical models when there is a beauti- ful theory based on quantum transport that is in agreement with experiment and involves only a few measurable parameters.” In his younger days only Bardeen’s family and close friends were aware of his hot temper because he revealed it so rarely. Typically he would vent against material objects, like golf balls or shoes. Only those close to him knew to interpret as rage the low-pitched hiss or sar- castic laugh that occasionally escaped through his teeth. But as he entered his eighties, cracks formed in his composure, and he was less able to moderate his temper when things really mattered to him. Tucker tried to avoid Bardeen while he worked out his own 

Pins and Needles and Waves 295 theory of CDWs. By the summer of 1987, Tucker was distinguish- ing his own “strong pinning” theory from tunneling. Tucker explained recently that “in strong pinning, every impurity stops the CDW from moving within a very small volume at each impu- rity site. The average phase remains constant, however, over much larger volumes containing a great many individual pinning centers, and phase-slip occurs at each site as the CDW moves along.” Hoping to convince Bardeen of the problems he saw in the quantum-mechanical theory of CDWs, Tucker prepared a carefully written account of his strong pinning theory. As Tucker’s theory won support, Bardeen felt even more iso- lated. “I think he felt betrayed,” recalled Salamon. Not since the days at Bell working with Shockley had Bardeen been seriously op- posed by one of his collaborators. “I think he felt that he’d brought Tucker here specifically to work on this, to confirm this, and then it turned out that [Tucker had] turned on [him].” Bardeen tried to help his opponents understand his quantum- mechanical theory. He worked hard to improve his arguments, but that also angered him because he felt he had already offered every- thing necessary to support the physics. Meanwhile Tucker was growing despondent and drained by his failure to explain his own theory to Bardeen. He worked with Miller to develop more con- vincing arguments. Bardeen opposed the work as unnecessary. When Tucker called for help from several physics colleagues, they claimed they could not understand the details of the theory and could not therefore pit themselves against Bardeen. Having difficulty in explaining a theory was not a new thing for Bardeen. More than fifty years earlier he had stumbled in his Princeton prelims when asked to detail how he arrived at the answer to one of Robertson’s questions. Bardeen’s collaborators, students, and occasionally his teachers had often stepped in to help John resolve his communication problems. But as he neared his eightieth birthday, no one was there to help him explain his theory of charge density waves. John’s easy friendship with Nick Holonyak offered a partial antidote to his intense frustrations in the latter part of 1987. When- ever Nick could see that John was feeling frustrated, he would encourage his friend to take a break and do something for himself. “Don’t let people constantly take your time,” Nick advised. “Look, if it’s a good day and you have such an inclination, go play golf.” 

296 TRUE GENIUS From September 21 to 25, 1987, Tucker attended the Second European Workshop on Charge Density Waves. It was held in Aussois, a picturesque ski village in the French Alps. Tucker spoke there about his strong pinning theory at a poster session on non- linear transport. Bardeen was home in Illinois. According to observers, the discussion of Tucker’s paper turned into a hot debate about the classical versus quantum-mechanical theories of charge density waves. Seeger reported witnessing “an ugly ceremony” in which a Hungarian physicist forced Tucker to “confess before the full audience that he would no longer support Bardeen’s CDW theory.” Also at the meeting was Tucker’s student Robert Thorne, who had recently taken a position at Cornell as an assistant professor. In a letter to Bardeen, Thorne described the “general feeling at the conference that, while not dead, the tunneling model seems unnec- essary for interpreting the experiments.” He expanded on the “con- sensus that weak pinning does not occur, and that strong pinning and phase slip play a dominant role in CDW transport.” He also remarked that Tucker appeared to him to be in a highly emotional state. Bardeen responded angrily to the reports. He called in Lyding and asked whether he thought Tucker was emotionally unbalanced. “I don’t think that’s true,” Lyding said. Lyding did think that get- ting things out in the open might be helpful. He hoped it “would lead to some kind of calm discussion between Tucker and Bardeen, and they would just resolve it, because they were talking.” So he mentioned Thorne’s letter to Tucker, who “went straight over to Bardeen and demanded to see the letter, and was very forceful about it.” John refused. Bardeen felt backed into a corner because Tucker was able to “talk fast and think on his feet,” Lyding explained. “My impres- sion is that Tucker made him feel very uncomfortable during all of this process when they were dealing with each other in person.” It was exceedingly difficult for Bardeen to “respond to that in real time” because he “was a very slow, deep-thinking, methodical type. And to have somebody chewing on your ideas when they’re com- ing out of your mouth is very unsettling.” By October 1987 the discussions between Bardeen and Tucker had became so heated that the two resorted to writing letters to each other. In his now shaky script, Bardeen insisted on October 

Pins and Needles and Waves 297 24, 1987 that the weak pinning “is confirmed by many experi- ments.” He was clearly exasperated: “These are simple conse- quences of quantum physics and the uncertainty principle and do not involve any deep ideas.” He suggested to Tucker that he had “developed a mental block on this problem that prevents you from thinking straight.” Later in the letter he urged Tucker to “put this problem aside for the time being and work on one that you should be able to make progress on.” Tucker was insulted. Lyding found himself in the role of Bardeen’s and Tucker’s “messenger boy.” He hoped “to provide just enough glue to keep those guys talking.” He recalled, “They were both upset. Bardeen would call me over to his office” and soon become “frustrated and angry that I wasn’t just accepting his point of view.” After a while “we’d get down into a calm discussion, and by the end of the meet- ing we’d be shaking hands.” But when Lyding delivered the mes- sage, “Tucker would usually write a letter and send it over to Bardeen.” A week or so later Bardeen would “call me over again.” Lyding sometimes scribbled notes while talking on the phone with Bardeen. One note read “diatribe.” Another read, “Blamed you for spilling the beans.” Still another, “Can’t reason with him.” Throughout this period Tucker was having back problems, which Bardeen claimed were psychosomatic. Bardeen tried diplomacy. In a November 6 letter to Tucker, he suggested that they “seem to be narrowing down our points of dif- ference.” Tucker did not think so. On November 8 he drafted a letter so emotionally charged that he did not dare to send it for six months. He felt that his reputation was on the line. And he had reached the end of his ability to deal calmly with Bardeen, who insisted that his central argument was “obviously correct as it stood.” Tucker admitted that Bardeen’s rage had shaken him. “I was actually afraid that you might drop dead in front of me.” In this letter, which he filed away but did not destroy, Tucker wrote that he felt, “you and I can no longer have any sort of positive interaction.” Unaware of Tucker’s incendiary letter of November 8, Bardeen wrote on November 13, “I hope that we can make progress in nar- rowing down our points of difference.” Tucker wrote back that Bardeen was ignoring available experimental facts. This unproduc- tive and hurtful exchange continued for ten more days. When Bardeen wrote on November 23, “I am glad that we agree that a 

298 TRUE GENIUS weak pinning model is required to account for the CDW data,” Tucker shot back, “Your statement that we now agree on the requirement for weak pinning could not be further from the truth.” Bardeen let a month go by before making his final move. On January 4 he wrote to the NSF and asked that his name be dropped from the grant with Tucker and Lyding. “Because of the change in emphasis of the work,” he explained, as well as “my advancing age and other obligations that I have, I find that I am unable to take an active part as co-director with John R. Tucker and Joseph W. Lyding.” By then the NSF had verbally committed to fund Tucker and Lyding alone. The money was subsequently granted, “with no strings attached.” The next day Bardeen informed Tucker that he was withdraw- ing from the CDW project. He again expressed his doubts about Tucker’s physics. Referring to their recent interactions, he wrote to Tucker, “You have by no means relieved my concerns. This I greatly regret because I am very grateful to you for initiating the CDW program here, for supervising the outstanding experimental work of John Miller that helped confirm the validity of your theory of photon-assisted tunneling as well as the beautiful work of Rob Thorne on phase-locking with combined a.c. and d.c. fields.” Reviewing some of the physics one last time, he referred to Tucker’s strong pinning theory as “a contradiction in terms.” He added, “There is nothing personal whatsoever. As I have told you many times, my every wish is to have you succeed. . . . I particularly regret any problems that this may cause the students, but see no other alternative than for us to go our separate ways.” Bardeen continued to work on CDWs alone. His confidence in the validity of his theory never wavered. He gave no ground when submitting his arguments on quantum depinning to the Physical Review early in February 1988. “No plausible classical model has been able to account for any aspect of CDW transport, d.c., a.c., or combined d.c. and a.c.” He argued that “any approach that does not treat CDW metals as macroscopic quantum systems misses the essential physics of the problem.” He called on theorists to pay more attention to experiment. “No sound prediction of classical CDW motion in the charge-compensated sliding regime is borne out by experiment. Experimenters and theorists alike should think of CDW motion as a beautiful example of macroscopic quantum mechanics, with many analogies to superconductivity.” The refer- ees called for revision. 

Pins and Needles and Waves 299 About this time Ravin Bhatt was visiting Illinois on a Bell Labs recruiting mission. When Bardeen saw Bhatt pass his office, he hur- ried out to speak with him. “I know you’re recruiting and you’ve got a lot of things to do and that it’s important for Illinois. But I think I finally got the tunneling theory of charge density waves all done. I have a BCS-like wave function for it.” Bardeen told Bhatt he was about to write the theory up, “but I want to try it out on you.” For roughly an hour the two sat together in Bardeen’s office and discussed charge density waves. Bhatt listened carefully while the 80-year-old enthusiastically unfolded his theory. Like most of Bardeen’s other colleagues, Bhatt could not understand the argu- ment. In May 1988, the month of Bardeen’s eightieth birthday, Tucker sent Bardeen his charged November 8 letter. The revised manuscript, received on October 24, 1988, was pub- lished with some light edits on Valentine’s Day 1989. “A consider- able body of evidence supports a theory based on quantum tunneling over macroscopic distances,” Bardeen wrote. “All evi- dence indicates that it is necessary to treat CDW metals as macro- scopic quantum systems with quantum tunneling as an essential feature.” Several months later Bardeen wrote bitterly to the Physical Review that in spite of the success of the tunneling theory of CDWs, “few other theorists have worked on the tunneling theory. It is not only not generally accepted by those in the field, but recent papers by leading experimentalists do not refer to the model as a possible explanation of the data.” He acknowledged that he had not expressed his ideas as well as he might have. “While I share part of the blame for this state of affairs in not writing clearly enough,” he said, “in large part it is a reflection on the present state of physics. Everyone is so busy doing his own thing that no one puts in the time required to get a real understanding of a diffi- cult subject.” He made the same point to Holonyak. “Everyone is so busy writing,” he told Holonyak, “and no one reads sufficiently, if at all, and knows little of what is already known.” The last of Bardeen’s single-authored papers on CDWs appeared in Physical Review Letters in May 1990. He followed up with a more general account in an article on “Superconductivity and Other Macroscopic Quantum Phenomena,” published in Physics Today in December 1990. That article “mattered a lot to him,” said his daughter Betsy. He considered it “in a way a culmination of that work.” By then the field had moved in the direction Bardeen 

300 TRUE GENIUS had opposed. Virtually everyone in the physics community had de- cided that CDWs were a “dirt effect.” No one has successfully defended Bardeen’s theory, but as Miller later remarked, a few isolated voices remind us that the clas- sical theory does not account for all the observed phenomena. It is not impossible that a complete theory may one day incorporate features that are quantum-mechanical along with others that are classical. Once or twice in the period from 1980 through 1991, when David Lazarus served as editor in chief for the American Physical Society, he learned that Bardeen had received a bad referee report. Having been Bardeen’s colleague since 1951, Lazarus found that surprising. When he investigated the reports, he found that indeed “the referee was totally out of line. I couldn’t believe it. I think it was some kid who thought it was sort of a cute thing to cut down an icon.” Lazarus acknowledged that “John really did have a hard time with the last few papers and it was not his fault at all. They were important papers, they did get published, but they gave him a harder time than he should have had.” Bardeen continued to fight in the trenches of his field long after he had won two Nobel prizes. Although his quantum-mechanical tunneling theory was not accepted as the explanation for charge density waves, the ideas he developed in his theory may prove ap- plicable in other contexts. Through his excitement and passion about the phenomenon being observed, Bardeen was one of the few who made a huge impact on the CDW field. He suggested crucial experiments and attracted many workers to the study of CDWs. Only Bardeen’s family and closest colleagues understood the force of his passion to do great physics. Perhaps that was because he said so little and appeared so ordinary in his everyday life. To most of Bardeen’s associates, and even to casual observers, there seemed no reason for him to keep on struggling so painfully through the rejection of his theory of CDWs. Psychologists claim such behavior is typical of the highly cre- ative person. The aging Bardeen, remarked Tucker, opened “him- self to a lot of criticism and a lot of abuse, which he got in spades, because he thought there was a possibility there was something out there that would really be a big breakthrough. He still had the yearning to do that kind of work.”