Portal de Periódicos da CAPES

Alfred Brian Pippard

2009; AIP Publishing; Volume: 62; Issue: 8 Linguagem: Inglês

10.1063/1.3206101

1945-0699

John Clarke,

Physics of Superconductivity and Magnetism

Alfred Brian Pippard, who pioneered the concept of nonlocal electrodynamics in normal and superconducting metals and was the first to map a Fermi surface, died in Cambridge, UK, on 21 September 2008, following a stroke.Brian was born in London on 7 September 1920. He spent his formative years in Bristol and attended Clifton Senior College, then considered the premier school in the country for teaching science, from 1934 to 1938. He was an undergraduate at Clare College, Cambridge, and earned his BA in physics in 1941. During World War II he made important contributions to the development of radar. He subsequently returned to Cambridge as a research student under David Shoenberg at the Royal Society Mond Laboratory, originally built for Pyotr Kapitsa in 1933. Brian received his PhD in physics in 1947 for his work on measurements of the surface impedance of superconducting and normal tin and mercury and of normal gold and silver. Staying at Cambridge, he moved progressively through the academic ranks and was elected Cavendish Professor of Experimental Physics in 1971. He remained in that position until his retirement in 1982. He was knighted in 1974.Brian had returned from World War II with an assortment of microwave components and set to work to exploit them. Using microwave resonators, he measured the real and imaginary parts of the surface impedance. From his results on normal metals, Brian developed the idea of the “anomalous skin effect,” which sets in when the electron mean free path exceeds the skin depth—the depth to which the microwaves penetrate. He realized that there must be a nonlocal relation between current and electric field, a seminal idea that was put on a firm theoretical footing by Harry Reuter and Ernst Sondheimer and by Robert Chambers. Brian’s most important result on superconductors derived from his measurements of the magnetic penetration depth in pure tin. He concluded that, analogous to the behavior in normal metals, the relation between the super-current and the vector potential was nonlocal, with a coherence length ξ This deduction demonstrated Brian’s extraordinary insight: The coherence length is a central parameter in the microscopic theory of superconductivity developed by John Bardeen, Leon Cooper, and Robert Schrieffer.While on sabbatical leave at the University of Chicago in 1955-56, Brian measured the anomalous skin effect in a large single crystal of copper for a variety of orientations. In a remarkable feat, he deduced the Fermi surface—the first-ever determination.Brian passionately believed that research and teaching went hand in hand. He felt that high standards of classroom teaching should be a requirement for faculty appointments and promotions. He played an ongoing role in revising the undergraduate teaching curricula at Cambridge. His interest in teaching extended to his supervision of research students and postdoctoral fellows. Although it is probably true that none of us ever won an argument with him because he was so quick-witted, he could be very kind and patient, and many of us recall with great affection his friendship and intellectual leadership.Brian had a great influence on Cambridge’s infrastructure. In 1966 he became the first president of Clare Hall. He oversaw the design of the college, which was founded to accommodate academic visitors of all disciplines during their sabbatical leaves. Clare Hall offered hospitality not only to its distinguished visitors but also to their families. Brian was also the driving force behind moving the Cavendish laboratory from its overcrowded site in the center of the city to its current site in West Cambridge. He was heavily involved in both fundraising for and the design of the new Cavendish. A guiding principle was that the design be sufficiently flexible to allow for laboratories to be reconfigured to accommodate new experiments and equipment. That idea has proved highly successful, and the laboratories have subsequently undergone many transformations.Perhaps Brian’s greatest strengths were his ability to pick the right experiment at the right time and his extraordinary insight into interpreting data without detailed calculations. Examples include his understanding of the coherence length in superconductors and his determining the Fermi surface of copper from largely geometrical considerations. But he never made use of the full formalism of quantum mechanics. When his graduate student Brian Josephson worked out the theory of Cooper pair tunneling between superconductors that was to win him a Nobel Prize, Brian claimed that he did not understand Josephson’s calculations.Aside from physics, Brian was a passionate piano player. He owned two grand pianos and played them until the last few months of his life. He loved to discuss and argue, as I well recall from the tea that he enjoyed with his students, postdocs, and colleagues almost every day. One of my favorite memories is a story he told about himself. After the war he served on a committee charged with naming various microwave components that had been invented for radar. A member of the committee proposed that one of them be named the “Pippard plate.” Feeling that a mild display of modesty was in order, Brian murmured (as I recall), “We can’t possibly call it that.” To Brian’s chagrin, the chair concurred: “No, I suppose we can’t!”Alfred Brian PippardCAVENDISH LABORATORY, CAMBRIDGE UNIVERSITYPPT|High resolution© 2009 American Institute of Physics.