The “Woodstock of Physics”

Posted by jns on 9 March 2007

There has been lots of talk, relatively speaking, this week about a now-famous event that took place at the annual meeting of the American Physical Society 20 years ago. The first piece that I saw was in the New York Times (Kenneth Chang, “Physicists Remember When Superconductors Were Hot“, 6 March 2007 — his piece is fine, but I think I’ll scream if anyone mentions mag-lev trains again in the same breath as superconductors, or anything else for that matter) about what quickly became known as “The Woodstock of Physics”, if you can imagine.

Today it’s the lead story in my e-mail’s “Physics News Update” (9 March 2007 edition), by Phil Schewe and Ben Stein of AIP (the American Institute of Physics is an umbrella organization that encompasses the American Physical Society, and publishes Physical Review and Physics Today, among others).

So this is the story that got everyone all excited twenty years ago. I wasn’t at that meeting — I usually attended a smaller local meeting the next month where most of my low-temperature colleagues congregated by tradition — but I certainly remember the buzz it created in the hallways near my lab. This is probably the event I will recall when people start talking again, as they seem to every generation or so, about how physics is pretty much played out and all important discoveries have already been made.

It was rather more excitement than you might expect to see among a group of typically staid physicists. By the way, this gives you a chance to see the differences between a news story written for the public, and one written with an audience of physicists in mind.

“THE WOODSTOCK OF PHYSICS,” 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.

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 [i.e., "Kelvins", centigrade sized degrees where 0 K is "absolute zero"]. 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. 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 YBaCuO 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 that superconducted at still higher temperatures or with a greater capacity for carrying currents. 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 YBaCuO 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.

(Photographs and an original summary press release from the 1987 meeting is available at our Physics News Graphics website, www.aip.org/png)