21st Century Science & Technology

John Bardeen, Superconductivity, And Edwin Hall’s Unanswered Questions
by Laurence Hecht

True Genius: The Life and Science of John Bardeen
by Lillian Hoddeson and Vicki Daitch
Washington, D.C.: Joseph Henry Press, 2002
Hardcover, 480 pages, $27.95

True Genius

Whether or not John Bardeen (1908-1991), the Nobel Prize-winning solid state physicist who developed the transistor, and the BCS (Bardeen-Cooper-Schrieffer) theory of superconductivity, is a “true genius,” this new biography is a useful account of his work. I read the book, hoping to get an overview of the historical development of modern solid-state theory, and to better understand the peculiar phenomenon of superconductivity. I got some of what I was looking for. As to coming to a clear understanding of the cause of superconductivity and such curious phenomena as the Meissner Effect, I ended not much closer than I have ever been on my long frustrating search of many years.

On the scale of things in postwar 20th Century science, Bardeen’s work is as good as any that I know of. For attempting a mastery of what that scoundrel Wolfgang Pauli called “the physics of dirt,” Bardeen wins my respect. As I had learned from some close encounters with the history of nuclear science, it was almost always the chemists who got there first, as with Marie Curie and radium, Chicago University’s William Draper Harkins’s 1919 recognition of the neutron, and German chemist Ida Noddack’s 1933 detection of nuclear fission by chemical analysis. The work of physicists, who assumed the task of probing the microphysical phenomena in the solid state, seems in some ways comparable, whether they would recognize it or not.

Yet there was also a measure of truth in Pauli’s ironic quip. Blackboard mathematical physicist that he was, one suspects Pauli recognized that the thatched-over composite we have come to know as quantum mechanics would not really hold up under close physical scrutiny. The devil was in the detail, and the task of adapting the never-too-sound theory to fit it was left to those who would dare.

Any modern description of superconductivity, or virtually any other solid state phenomena, seems to derive in some way, as Bardeen notes, from the early 1930s work of those three small teams of collaborators that took up this project—Eugene Wigner’s students at Princeton, John Bardeen and Fred Seitz; John Slater’s group at the Massachusetts Institute of Technology; and Lennard-Jones, Mott, and Jones at Cambridge, for better, or for worse.

AT&T Archives
The team of Brattain, Bardeen and Shockley at Bell Labs during the development of the transistor. Brattain (left) is at the apparatus, while Bardeen (right) enters data into their notebook, and Shockley looks on.

The Transistor and Shockley
To understand any scientific subject, an historical development is indispensable. The merit of this work is in the historical recounting of the modern development of the field. The enormous contribution to postwar science deriving from the wartime research efforts at the MIT “rad lab” and the Manhattan Project are ever evident. The chapter on the development of the transistor at Bell Labs is especially clear and informative. By telling the story of this invention in a way one suspects it might have happened, one learns more than many textbook pages can ever convey.

The balanced treatment of the imbalanced William Shockley, who went off to Harvard in the mid-1950s, after having contributed to the development of the transistor, to refound race “science,” is also welcome. One is pleased to learn that Bardeen despised the racial IQ theories of his former collaborator (a collaboration that had become so strained by Shockley’s maniacal egotism that Bardeen finally left Bell Labs to avoid it).

What is disappointing about it all is, and is not, the authors’ fault. The acceptance of the irrational, positivist view—something to the effect of “all that we know is what we can measure, and to look for causality is a waste of time”—is the tragedy of science in the post-1927 Solvay Conference era. As in all true tragedy, the problem is not some set of circumstances dictated from without, but rather the refusal on the part of those living it to break with the underlying assumptions which lead them, with each step, deeper into the pit of an ugly irrationality that mocks the very purpose of science.

In the development of the transistor, a fortunate accident, the condensation of water on a semiconducting surface in some photovoltaic effect experiments, led Walter Brattain to recognize the possibility of controlling the current through a semiconductor, in a way similar to what was accomplished by the grid in a vacuum tube. This led to Bardeen’s proposed field effect amplifier of Nov. 21, 1947, shown in this diagram.

Thus, in my view, the very strength of the book, its detailed portrayal of how modern physics is done, is also its shortcoming. For in the end, there is a lack of beauty to the final result that no amount of writing and research skill can overcome.

John Bardeen is the only winner of two Nobel Prizes in physics, first with William Shockley and Walter Brattain for the transistor, then with Leon Cooper and J. Robert Schrieffer for the BCS theory of superconductivity. Does he represent “true genius?” I found that aspect of the book, deriving from its title, to be the most annoying—almost as annoying as it was to learn of the new academic discipline known as “scholars of genius and creativity.” (The “of” refers to object not subject.)

I cannot differ with the author’s concluding words on the subject: “They are real people, highly motivated to develop the human elements of genius that exist potentially in all of us.” Yet, to separate the question of the cultivation of genius from the classical standards of education and moral practice which we have all but abandoned as a nation, seems to me inexcusable.

If one accepts the popular premise that the award of a Nobel Prize is the unfailing measure of true genius, I suppose the case for Bardeen is open and shut, twice. If one questions such assertions, and prefers a universal standard of truth, then the currently faddish preoccupation of historians of science to arrive at a definition of genius by sociological means appears a silly spectacle. I suspect that feeling may even be shared by many among those who have become the subject of such academic games, be they living or dead. I would like to think the ever modest Dr. Bardeen might even agree with me on that score.

Postscript: Have Hall’s Questions Been Answered?
Shortly after completing the above review, a photocopy of a 1933 paper by Edwin H. Hall on the subject of superconductivity1 more or less fell out of a file folder into my hands: “I venture to raise two questions, each perhaps heretical, concerning metals in the supraconductive state,” Hall begins, thus instantly capturing my attention. “The first relates to the Hall effect; the second will be stated somewhat later.”

It was the second question that most interested me:

“Is there conclusive evidence that the persistent currents which Ounes and others have observed are anything more than the aggregate of microscopic electric whirls within the metal? Is there conclusive evidence that the persistent current which is ordinarily assumed to be circumferential within a supraconductive ring or shell is really circumferential?” Hall asks.

The fact that this question could still be asked in 1933, and by no less a figure than the discoverer of the Hall Effect and Harvard’s senior expert on electron conduction, seemed astounding. For the London theory of superconductivity, put forth in that year, and upon which all the rest of the theoretical superstructure, including Bardeen’s work is built, assumes the very thing that Hall here challenges.

A basic assumption of the theory is the hypothesis of Kammerlingh Onnes (Ounes) which had the support of Lorentz, that the superconducting electrons flow in channels or tubes, the walls of which preclude transverse motion. Today this is sometimes described as a macroscopic quantum state. Is it possible that the whole modern theory is based on a mistaken interpretation?

Hall’s probing analysis of the experimental evidence which led, or perhaps misled, Onnes to the assumption of these circumferential, tubular currents is compelling, and seems worth reproducing here:

“As bearing on this question I will quote two passages from the 1924 Solvay Conference paper of Ounes. On p. 251 of the Conference Report, he speaks of an experiment of Mr. Langevin “où une bobine à circuit ouvert montrait un courant persistant” [where a coil in open circuit would show a persisting current—LH]. On pp. 263 and 264 he describes an experiment of his own made with a ring consisting of 24 alternative sectors of tin and lead. These metal sectors, which were soldered together, were thin layers covering a ring of ivory, the junctions between them being on radii of the ring. “Le courant [persistent] fut établi avec un champ perpendiculaire au plan de l’anneau, puis celui-ci fut tourné d’un angle de 30°. Nous avions pensé que nous trouverions un courant qui s’étendrait au bout d’un certain temps [because the soldered junctions were not supposed to be supraconductive] mais l’expérience a montré que des courants continuaient à circuler dans l’anneau et, lorsque l’experience fut répéteé avec l’anneau coupé, celui-ci montra le même moment magnétique.” [The (persisting) current was created by a field perpendicular to the plane of the ring, which was then rotated by 30°. We had expected to see the current expend itself after a certain time (because the soldered junctions were not supposed to be supraconductive) but the experiment showed that the currents continued to circulate in the ring and, when the experiment was repeated with a cut ring, this showed the same magnetic moment—LH.]

“A chain being no stronger than its weakest link,” Hall continues, “it seems probable that local currents of very limited radius would be more likely to persist than currents having a long cyclic path. Currents of the latter description may well be induced in a supraconductor when the original penetrating magnetic field is varied but they are likely to die out sooner than the local whirls of current. Is it not reasonable to suppose that we have here an explanation of the fact noted by Ounes, on p. 255 of the Solvay Report, that just after a change of the imposed magnetic field the induced current “varie encore un peu?” [still varies a little—LH].

“I must, of course, speak very cautiously of this matter, for I have never even seen an experiment on supraconductivity. It seems to me, however, that, for example, the conclusions reached by McLennan [Phil. Mag. 168-180, July (1932)] and his co-workers as to the existence and strength of circumferential persistent currents in small rings of tantalum, lead, and tin, respectively, are open to question. These investigators make no mention of the possibility that the currents are not circumferential. They assume them to be circumferential and on this assumption estimate their strength, from the observed magnetic torque between each supraconductive ring and a neighboring coil of copper wire carrying a current. I believe, however, that all of the phenomena they describe are quite consistent with the supposition that the persistent currents were local whirls within the metal rings, not circumferential currents at all.

“Apparently a test of the question here raised could be made by determining the direction and intensity of the magnetic field along an axis common to the ring and the surrounding coil of current-bearing wire. The investigators assumed, I believe, that the magnetic flux along the axis was zero after the persistent current in the ring was established. If my idea of the matter is correct, there should be along this axis a permanent flux corresponding to the direction of the current circulating in the copper coil,” Hall concludes.

We do not know if Hall’s test was ever made. If not, there is some considerable explaining to be done. (And even so, there is much yet to explain, some also relating to the first of Dr. Hall’s “heretical questions,” wherein he seems to provide the explanation for the not-yet-demonstrated Meissner Effect.)

In either case, one finds in Hall’s comments the true spirit of physics, so hard to find today. How the old master proves himself here, at age 78, every bit as sharp and unwilling to be humbugged as he was at age 24, in 1879, when he made the discovery which both bears his name, and has proved itself an indispensable tool in solid state research, by questioning the truth of a passage in Maxwell’s famous textbook.

1. E.H. Hall, 1933. “On Supraconductivity and the Hall Effect,” Proc. Nat. Acad. Sci., Vol. 19, p. 619-623.

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