J. Robert Schrieffer (1931–2019) Physicist Who Shared Nobel for Theoretical Basis of Superconductivity

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OBITUARY COMMENT J. Robert Schrieffer (1931–2019) Physicist who shared Nobel for theoretical basis of superconductivity.

he story of how Robert Schrieffer Birmingham, UK. He held faculty positions solved a problem that had resisted at the University of Chicago, the University the best minds in physics for more of Illinois and the University of Pennsylvania. Tthan 40 years, while riding the New York Throughout his career, Schrieffer displayed BETTMAN/GETTY subway, is the stuff of legend in some the same flair as in his brilliant wave func- circles. His explanation of how supercon- tion insight. In 1979, he and his colleagues ductivity works earned him a share of the showed that certain conducting polymers 1972 Nobel Prize in Physics. A former could exhibit excitations with electrical president of the American Physical Society charge, but no spin (the magnetic moment of (APS), Schrieffer died on 27 July, aged 88. each electron is called its spin). The opposite In 1911 it was discovered that certain could also occur: excitations could have spin, metals, when cooled to low enough but no charge. It was a revelation that the two temperatures, can carry current with no fundamental properties of electrons, charge resistance. This seemingly miraculous and spin, could be split apart. This decon- property, superconductivity, arises directly struction has since been discovered at many from quantum mechanics, and underlies other frontiers of condensed-matter physics. many contemporary technologies, such as A later collaboration showed that a second magnetic resonance imaging body scan- example of deconstructed electrons, the frac- ners and particle accelerators. For decades, had studied the effect of phonons (quantized tionally charged excitations in the fractional however, there was no theory to explain sound waves) on metals, showing that they quantum Hall states, also exhibit fractional how electrons in superconducting materi- mediated an attractive interaction between statistics, meaning that they are not the als overcome their own mutually repulsive electrons. Cooper found that this attractive conventional bosons or fermions that were properties and other causes of resistance. interaction could lead to the formation of thought to divide all fundamental particles In early 1957, Schrieffer, then a 25-year- bound pairs of electrons. However, Cooper’s into two classes. old graduate student, wrote down a theory described only the formation of a In 1980, he moved to the University of quantum-mechanical wave function that single electron pair. The question remained California, Santa Barbara, and joined the accounted for the behaviour of electrons in how to describe the many electrons pair- newly formed Institute for Theoretical Phys- superconductors. With his thesis adviser ing in the full electronic state of the metal, ics. Here, between 1984 and 1989, he served John Bardeen and postdoc colleague Leon and why such pairing would lead to the as its second director, helping to establish its Cooper, he published the now-famous properties of a superconductor. strong reputation as a centre for theoretical BCS wave function and the full theory of Schrieffer’s intuitive leap came to him on physics research. His final move in 1992 was superconductivity less than a year later — the subway while attending an APS meeting back to Florida, where he took a state-wide named BCS after the trio, who shared the in 1957. It struck him that a natural wave professorial position in the Florida State Uni- Nobel prize (J. Bardeen, L. N. Cooper and function for describing a state with elec- versity System. From that year until 2006 he J. R. Schrieffer Phys. Rev. 108, 1175; 1957). tron pairing was one in which the number was the first chief scientist of the National The work has had far-reaching conse- of electrons was not fixed, but had a certain High Magnetic Field Laboratory at Florida quences for both fundamental science and quantum mechanical uncertainty. He wrote State University in Tallahassee, where he had practical technology. Schrieffer continued it down there and then. This key insight, a crucial role in establishing the new facility’s to make foundational contributions to our radical at the time but now part of the stand- scientific credentials. His 1996 APS presi- understanding of electrons in solids. ard toolkit of theoretical physics, cracked dency was marked by his efforts to improve Born in Oak Park, Illinois, in 1931, the problem wide open. With the wave func- communication between the physics commu- Schrieffer studied physics at the Massachu- tion in hand, it quickly became possible to nity and the public, and between physicists setts Institute of Technology in Cambridge calculate many of the observed properties of themselves to help unify the field. as an undergraduate. It was at graduate superconductors, and to predict new proper- Schrieffer was equally known for his school at the University of Illinois at ties, which were subsequently found. warmth, charm, generosity and brilliance. Urbana-Champaign that he began working Schrieffer’s beautiful idea has contributed When Bob discussed physics, his eyes would with Bardeen, who in 1956 had just won a to many branches of fundamental physics. In twinkle and a boyish demeanour would shine share of the physics Nobel for the invention condensed-matter physics, it has also been through. This enthusiasm and provision of of the transistor. applied to superfluid helium-3 and cold-atom wise counsel to younger physicists never Bardeen suggested Schrieffer try his hand systems. Elsewhere, the theory has helped to waned. His unique style is captured, as if in at understanding superconductivity. This explain complex nuclei and neutron stars, a photograph, by the BCS wave function. ■ was a risky proposition. After the initial and played a crucial part in establishing the success of quantum theory in describ- understanding of quantum field theory that Nick Bonesteel and Gregory Boebinger ing ordinary conductors, insulators and underlies today’s standard model of strong, are professors of physics who were colleagues semiconductors, there had been countless electromagnetic and weak interactions. of Schrieffer’s at the National High Magnetic attempts to explain superconductors and Schrieffer went on to take postdoc- Field Laboratory and Florida State University. all had failed. But the timing was right. toral positions at the Niels Bohr Institute e-mails: [email protected]; Bardeen, with his then-postdoc David Pines, in Copenhagen and at the University of [email protected]