John Robert Schrieffer (1931–2019)

John Robert (“Bob”) Schrieffer, one of the leading theoretical physicists of the past century, passed away on 27 July. He was 88. His seminal work with physicists John Bardeen and Leon Cooper earned them the Nobel Prize in Physics in 1972 and is now the accepted the theory of superconductivity. The Bardeen-Cooper-Schrieffer (BCS) theory solves one of the major scientific problems of the early 20th century and has been foundational for many important developments in physics since. Born in Oak Park, Illinois, on 31 May 1931, Bob's family moved to New York and then to Florida. He remained fond of Florida, eventually returning in 1992 as a professor at Florida State University. He received a bachelor of science degree in physics from the Massachusetts Institute of Technology in 1953. There, under the guidance of John Slater, he became interested in solid-state physics. He did his graduate work with physicist John Bardeen at the University of Illinois Urbana–Champaign (UIUC). When he went to see Bardeen about a possible thesis problem, Bob later recounted, Bardeen pulled out a paper from his desk with a list of 10 possible projects. At the bottom of the list was “superconductivity.” Bob received his Ph.D. in physics from UIUC in 1957 and went on to postgraduate fellowships at Copenhagen's Niels Bohr Institute and England's University of Birmingham. While at the Bohr Institute, he met Anne Grete Thomsen; they were married in 1960. His next positions were at the University of Chicago and then the physics department at UIUC. In 1962, Bob joined the University of Pennsylvania physics department, where he remained for almost two decades. In 1980, he took a position at the University of California, Santa Barbara (UCSB), physics department and at the National Science Foundation's Institute for Theoretical Physics (ITP), also in Santa Barbara. Bob served as the second director of the ITP and played an important role in its development into the major center for theoretical physics that it is today. Superconductivity is responsible for spectacular quantum phenomena on a macroscopic scale. A superconductor supports a “persistent current”—a current that can flow forever without requiring any input of energy. Moreover, table-top superconducting devices can exhibit quantized behaviors that directly, and with apparently infinite precision, reflect the fundamental constants of nature that define quantum mechanics on the microscale. Superconductivity was first observed in 1911, and all the greatest theorists attempted to explain it in the decades after the invention of quantum mechanics. The solution required a leap of imagination. Bob achieved the mathematically simple but conceptually profound step when he wrote down an explicit wave function—one that violates the otherwise immutable principle of particle number conservation. This opened the door to a number of successful predictions of the BCS theory. ![][1] PHOTO: NATIONAL HIGH MAGNETIC FIELD LABORATORY Extensions of the original BCS work—many of them carried out by Bob with various junior collaborators—led to an increasingly detailed (microscopic) theory. In addition to its direct role as a theory of superconductivity, the BCS theory led to great successes in theoretical physics that crossed subdisciplines. In nuclear physics, it played a central role in the understanding of the structure of complex nuclei and of neutron stars. It also played a vital role in reaching the modern understanding of the quantum field theory that underlies today's standard model of strong, electromagnetic, and weak interactions. It was characteristic of much of Bob's work that the calculations were simple and explicit, whereas the implications were broad and deep. His work on solitons in conducting polymers was broadly important, leading to the first concrete realization of a system that exhibits fractionalized charge and initiating inquiry into the implications of topology for the electronic properties of matter. Yet, the key calculations are so simple that they now are given as homework assignments in introductory courses on condensed-matter physics. Other examples are the “Schrieffer counting argument” for computing the charge of a topological excitation as a fraction of the fundamental electron charge, and the demonstration, in collaboration with physicists Frank Wilczek and Daniel Arovas, that the quasiparticles in the famous Laughlin state for the fractional quantum Hall effect have not only fractional charge but fractional braiding statistics. These works form important pieces of the intellectual foundation of many later developments concerning the interplay of quantum mechanics and topology for the emergent properties of macroscopic systems, including solitons in polyacetylene, quantum Hall devices, and topological insulators. We were both fortunate to have been Bob's postdocs. D.S. was his first postdoc at the University of Pennsylvania, and S.A.K. was his last postdoc there and moved with him to UCSB to become his first California postdoc. D.S. had moved to UCSB 12 years earlier and played a role in convincing Bob to move there. Somehow, despite being inordinately busy, Bob always had time for us. Often, while we were all at UCSB, he would have lunch with us and with any interesting visitors who were present, and then we would all go for a leisurely walk around the lagoon, delighting in the views and discussing physics. Bob was known to be a statesman of science without a personal agenda. Confidence in his leadership derived from a universal acceptance and belief in his ability and personal integrity. Beyond this, those fortunate to have known him will remember his patience, kindness, and the ever-present twinkle in his eye. They also know how he suffered from the highs and lows of the bipolar disorder that took over his life at the end. In addition to his remarkable intellect and physical insight, we remember Bob as a mentor and later a friend, whose determination, bordering on stubbornness, accompanied by good-natured optimism when physics became difficult, was cherished by all who knew him. [1]: /embed/graphic-1.gif