|
The famous session at the March 1987
meeting of the American Physical Society, earned its nickname
because of the rock-concert fervor inspired by the convergence of
dozens of reports all bearing on copper-oxide superconductors. The
20th anniversary of this singular event was celebrated this week at
the APS meeting in Denver.
 Front row, left to right: Michael Schluter, Malcolm Beasley (Stanford), unidentified, Morrel Cohen (Chicago). Third row center Philip Anderson (Princeton); far right (silver hair), Paul Grant (IBM). Photo: AIP
Why such an uproar over the electrical properties of an unlikely
ceramic material? Because prior to 1987 the highest temperature at
which superconductivity had been observed was around 23 K. And
suddenly a whole new set of compounds-not metallic alloys but
crystals whose structure put them within a class of minerals known
as perovskites---with superconducting transition temperatures above
35 K and eventually 100 K generated an explosion of interest among
physicists. Because of the technological benefits possibly provided
by high-temperature superconductivity (HTSC)---things like bulk
power storage and magnetically levitated trains---the public was
intrigued too.
This week’s commemoration of the Woodstock moment (the months of
feverish work leading up to the 1987 meeting) provided an excellent
history lesson on how adventurous science is conducted. Georg
Bednorz (IBM-Zurich), who with Alex Mueller made the initial HTSC
discovery, recounted a story of frustration and exhilaration,
including working for years without seeing clear evidence for
superconductivity; having to use borrowed equipment after hours;
overcoming skepticism from IBM colleagues and others who greatly
doubted that the cuprates could support supercurrents, much less at
unprecedented temperatures; and finally arriving at the definitive
result---superconductivity at 35 K in a La-Ba-Cu-O compound.
 Brian Schwartz (Brooklyn College and APS), center, explains the new superconductivity developments to Paul Raeburn of the Associated Press (to Schwartz's right) and, to Schwartz's left, Edward Edelson of the New York Daily News, Phillip Schewe of AIP, and Dietrick Thomson of Science News. Photo: AIP
In October 1986 Bednorz and Mueller prepared a journal article
confirming their initial finding in the form of observing the
telltale expulsion of magnetism (the Meissner effect) from the
material during the transition to superconductivity. Submitting
this paper, however, required the approval of the IBM physics
department chairman, Heinrich Rohrer who, that very week, had been
declared a co-winner of the Nobel prize for his invention of the
scanning tunneling microscope (STM). Afraid that he would not be
able to obtain the preoccupied Rohrer’s attention, Bednorz obtained
the needed signature by thrusting the approval form at Rohrer as if
he (Bednorz) desired only a celebratory autograph. A scant year
later Bednorz and Mueller pocketed their own Nobel Prize.
The IBM finding was soon seconded by work in Japan and at the
University of Houston, where Paul Chu, testing a Y-Ba-Cu-O compound,
was the first to push superconductivity above the temperature of
liquid nitrogen, 77 K. Very quickly a gold rush began, with dozens
of condensed matter labs around the world dropping what they were
doing in order to irradiate, heat, chill, squeeze, and magnetize the
new material. They tweaked the ingredients list, hoping to devise a
sample superconducted at still higher temperatures or with a greater
capacity for carrying currents.
 Linus Pauling (formerly of Caltech) at a press conference about quasicrystals. Photo: AIP
At this week’s APS meeting Chu said
that he and his colleagues went for months on three hours’ sleep per
night. Several other speakers at the 2007 session spoke of the
excitement of those few months in 1987 when-according to such
researchers as Marvin Cohen (UC Berkeley) and Douglas Scalapino (UC
Santa Barbara)---the achievement of room-temperature superconductivity
did not seem inconceivable.
The Woodstock event, featuring 50 speakers delivering their fresh
results at a very crowded room at the New York Hilton Hotel until
3:15 am, was a culmination. In following years, HTSC progress
continued on a number of fronts, but expectations gradually became
more pragmatic. Paul Chu’s Y-Ba-Cu-O compound, under high-pressure
conditions, still holds the transition temperature record at 164 K.
Making lab samples had been easy compared to making usable
power-bearing wires in long spools, partly because of the brittle
nature of the ceramic compounds and partly because of the tendency
for potentially superconductivity-quenching magnetic vortices to
form in the material.
Paul Grant, in 1987 a scientist at
IBM-Almaden, pointed out that HTSC applications have largely not
materialized. No companies are making a profit from selling HTSC
products. Operating under the principle of “You get what you need,”
Grant said, superconducting devices operating at liquid-nitrogen
temperatures weren’t better enough so as to displace devices
operating at liquid-helium temperatures.
Nevertheless, the mood of the 2007 session (Woodstock20) was
upbeat. Bednorz said the 1986/87 work showed that a huge leap
forward could still take place in a mature research field whose
origins dated back some 70 years. Bednorz felt that another wave of
innovation could occur. Paul Chu ventured to predict that within
ten years, HTSC products would have an impact in the power
industry.
Paul Grant referred to the study of superconductivity as
the “cosmology of condensed matter physics,” meaning that even after
decades of scrutiny there was still much more to learn about these
materials in which quantum effects, manifested over macroscopic
distances, conspire to make electrical resistance vanish, a
phenomenon which at some basic level might also be related to the
behavior of protons inside an atomic nucleus and the cores of
distant neutron stars.
The summary press release of the meeting, prepared by Phillip Schewe of AIP
Source: AIP
|
