True Genius The Life and Science of John Bardeen: The Only Winner of Two Nobel Prizes in Physics (2002) / Chapter Skim
Currently Skimming:
15 Pins and Needles and Waves
15 Pins and Needles and Waves
Pages 284-300
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 284... ...
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" i, ost physicists accept aging as the ultimate obstacle in \' research.
|
From page 285... ...
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 proceeds inside them along linear chains that hardly interact with one another. One of the experimentalists working in the field of CDWs was George Gruner at the University of California at Los Angeles (UCLA)
|
From page 286... ...
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 demonstrated such pinning and depinning in a classic experimental study involving charge density waves created in the inorganic linear chain compound NbSe3.
|
From page 287... ...
, 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 socalled classical model of an overdamped oscillator motion in a periodic potential.
|
From page 288... ...
Bardeen told Tucker that he thought charge density waves were a macroscopic quantum phenomenon. He explained why he suspected that PAT might help to explain their transport.
|
From page 289... ...
program at Illinois' Materials Research Laboratory, which was supporting 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.
|
From page 290... ...
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.
|
From page 291... ...
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 meetings. 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 disrespect from the younger generation.
|
From page 292... ...
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.
|
From page 293... ...
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 community.
|
From page 294... ...
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 attractive 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 article on the work to Physical Review Letters. "Boy I'm glad this high-Tc came out," Salamon recalled thinking, "because it will take lohn'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 working 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.
|
From page 295... ...
Tucker explained recently that "in strong pinning, every impurity stops the CDW from moving within a very small volume at each impurity 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.
|
From page 296... ...
" 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 unnecessary for interpreting the experiments." He expanded on the "consensus 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.
|
From page 297... ...
" Unaware of Tucker's incendiary letter of November 8, Bardeen wrote on November 13, "I hope that we can make progress in narrowing down our points of difference." Tucker wrote back that Bardeen was ignoring available experimental facts. This unproductive and hurtful exchange continued for ten more days.
|
From page 298... ...
"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.
|
From page 299... ...
"All evidence indicates that it is necessary to treat CDW metals as macroscopic 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.
|
From page 300... ...
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 applicable 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.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.