The Postdoc, the Pottery, and the Levitating Magnet

The Mechanism

Superconductivity — the phenomenon in which an electrical current flowing through a material encounters *exactly zero resistance* and the material expels any external magnetic field (the Meissner effect) — was discovered in 1911 by Heike Kamerlingh Onnes in Leiden, in pure mercury cooled to 4.2 K with liquid helium (the same liquid Onnes had succeeded in producing for the first time three years earlier). It is a *macroscopic quantum phenomenon* — quantum-mechanical coherence appearing in a piece of metal large enough to hold in your hand. The microscopic mechanism was unknown for forty-six years. In 1957, three American physicists at the University of Illinois — John Bardeen, Leon Cooper, and J. Robert Schrieffer — published the theory now called *BCS theory* (Bardeen-Cooper-Schrieffer), explaining superconductivity in conventional metals as the formation of weakly-bound electron pairs (now called *Cooper pairs*) by an attractive force mediated by lattice vibrations (*phonons*) of the underlying crystal. The Cooper pairs, behaving as composite bosons rather than as individual fermions, condense into a macroscopic quantum state at low temperatures and carry electrical current with zero resistance. The 1972 Nobel Prize in Physics went to Bardeen, Cooper, and Schrieffer for the theory (Bardeen's *second* physics Nobel — his first had been in 1956 for the transistor; he is the only person to have won the physics Nobel twice). BCS theory had a critical prediction: the superconducting transition temperature *T_c* (the temperature below which the material superconducts) has a theoretical upper bound set by the phonon spectrum and the electron-phonon coupling. By the early 1970s, after a decade of focused alloy-development work, the highest known *T_c* in any material was about 23 K in niobium-germanium (Nb₃Ge), reached in 1973. By 1980, no further increases had been achieved despite intensive search. A widespread theoretical consensus had hardened: BCS-mediated superconductivity was limited to about 30-40 K at the very most. Higher transition temperatures, if they existed, would require a *different mechanism* — and there was no theoretical evidence that such a mechanism was possible. By the mid-1980s, superconductivity research was no longer a fashionable area. The two physicists who broke the ceiling worked at the IBM Research Laboratory in Rüschlikon, on the southwestern shore of Lake Zurich. The older, *Karl Alexander Müller* (always *K. Alex Müller*), was born in Basel in 1927, took his physics doctorate at ETH Zurich in 1958 under Wolfgang Pauli, and joined IBM Zurich in 1963. By 1985 he was an IBM Fellow — the laboratory's highest technical rank — focused on ferroelectric and magnetic perovskites (a class of mixed-metal oxide crystals with the structure of the mineral perovskite, CaTiO₃). The younger, *Johannes Georg Bednorz*, was born in Neuenkirchen, West Germany, in 1950, took his physics doctorate at ETH Zurich in 1982 under Müller and Heini Granicher, and joined IBM Zurich in 1982 as a research staff member. In late 1983, Müller suggested to Bednorz that they search systematically for superconductivity in *complex copper oxides* — materials nobody else in the field thought worth investigating. The choice was driven by a theoretical hunch: in certain copper-oxide perovskites, the strong on-site Coulomb repulsion in the copper-oxygen plane (combined with the partial filling of the copper *d* electron band) might support an unconventional pairing mechanism via *Jahn-Teller distortions* (a coupling between electronic orbital states and lattice distortions, distinct from the phonon-mediated coupling in BCS). The hunch had no experimental backing in 1983. Müller and Bednorz spent two and a half years synthesizing variants of barium-lanthanum-copper-oxide and related materials, measuring their resistance as a function of temperature, and finding nothing superconducting. The breakthrough came in mid-January 1986. Bednorz, working alone in the lab, synthesized a ceramic pellet of nominal composition La₂₋ₓBaₓCuO₄ (precise stoichiometry x ≈ 0.15-0.25 in various samples), pressed and sintered at about 900-1000 °C, with a resistance-vs-temperature measurement on January 27, 1986. The resistance dropped sharply at about 11 K. By April 1986, with better-controlled samples, the drop had moved to 30-35 K. Whether the drop represented a *true* superconducting transition (a phase coherent across the bulk of the sample, with zero resistance, expelling external magnetic field) or merely a metallic anomaly was unclear from the resistance data alone. Müller and Bednorz, working in increasing secrecy through the spring and summer of 1986, deliberately published their result in the relatively low-profile German-language journal *Zeitschrift für Physik B* — to avoid alerting the better-resourced American and Japanese groups working on superconductivity, who would, if they saw the result in *Physical Review Letters* or *Nature*, immediately mobilize their entire apparatus to confirm or to surpass it. The paper, Bednorz, J.G. & Müller, K.A., "Possible high T_c superconductivity in the Ba-La-Cu-O system," *Zeitschrift für Physik B* 64(2): 189-193, was received on April 17, 1986, and published in September 1986. The title's careful "*Possible*" reflects Müller's caution: the resistance data alone did not yet establish a Meissner effect, the second hallmark of superconductivity. By autumn 1986 several other laboratories had begun to take the *Zeitschrift* paper seriously and to attempt to reproduce the result. The decisive confirmation came on November 26, 1986, when Shoji Tanaka's group at the University of Tokyo independently reproduced the LBCO result and, critically, demonstrated the Meissner effect — confirming that LBCO was a true superconductor, not a metallic anomaly. The race was on. Within two months, in January and February 1987, two American laboratories — one at the University of Houston led by Ching-Wu (Paul) Chu and one at the University of Alabama in Huntsville led by Maw-Kuen Wu, in collaboration — discovered that replacing the lanthanum in Bednorz and Müller's compound with the much smaller yttrium yielded a new material, YBa₂Cu₃O₇, with a superconducting transition temperature of *92 K* — for the first time *above the boiling point of liquid nitrogen* (77 K). Liquid nitrogen costs cents per liter, and is the cheapest cryogenic liquid commercially available; liquid helium, by contrast, costs about $10-30 per liter. A superconductor whose operating temperature is above 77 K is, for the first time, *practically deployable* with reasonable cooling cost. The discovery of YBa₂Cu₃O₇ — universally called *YBCO* — was the breakthrough that turned a Swiss-laboratory curiosity into a global technological program. The American Physical Society's annual March Meeting in 1987 — informally known thereafter as *the Woodstock of Physics* — was held in New York on March 18, 1987, with a special evening session on cuprate superconductivity that ran until 3:15 a.m. and saw two thousand physicists pack the Sutton Ballroom of the New York Hilton. Bednorz and Müller were awarded the 1987 Nobel Prize in Physics — announced on October 14, 1987, *thirteen months* after the *Zeitschrift* paper was published. It was the fastest physics Nobel in the prize's history. The citation was *for their important breakthrough in the discovery of superconductivity in ceramic materials*. The Stockholm ceremony was on December 10, 1987. Müller, then 60, dedicated his Nobel lecture to the memory of his graduate-school supervisor Wolfgang Pauli, who had died in 1958. Bednorz, then 37, was the youngest physics Nobel laureate since 1980. The *theoretical* problem — the question of *how* the cuprate ceramic superconducts at 92 K, what mechanism is doing the work, how the Cooper pairs form when the BCS phonon mechanism is plainly inadequate — has not been solved. The current best models invoke *spin-fluctuation-mediated pairing* (an antiferromagnetic precursor state in the cuprate copper-oxygen plane providing the attractive interaction, distinct from BCS phonon-mediated coupling), but no single mechanism is fully accepted by the cuprate-physics community in 2026. The phenomenology — the phase diagram with its pseudogap, its strange-metal normal state, its anti-d-wave superconducting state — is documented in extraordinary detail. The microscopic mechanism is, in 2026, one of the longest-standing open problems in condensed-matter physics: forty years after the discovery, we know how the material behaves in great quantitative detail and we do not know why. The other surprise of the cuprate story is the *Tc ceiling*. After YBCO at 92 K (1987), further cuprate variants pushed the Tc to 110 K (BSCCO, 1988), 125 K (TBCCO, 1988), and 138 K (HgBaCaCuO, 1993 — the current cuprate record at ambient pressure). Higher transition temperatures have since been reported in completely different materials: H₃S at 203 K under 150 GPa (2015), LaH₁₀ at 250 K under 170 GPa (2019), and (controversially, with retracted papers) various hydrogen-rich compounds claimed at room temperature under extreme pressures. Room-temperature superconductivity at ambient pressure has not been achieved as of 2026. The cuprate ceramics remain, sixty-five years after Onnes's first liquid-helium-cooled mercury experiment in 1911 and forty years after Bednorz and Müller's furnace at Rüschlikon, the most-studied and least-understood electronic material in physics.