Sizing Up the Fermi Surface: Brian Pippard Speaks of Metals, Methods, and Songs
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Sizing Up the Fermi Surface: Brian Pippard Speaks of Metals, Methods, and Songs
Sir Brian Pippard, a most distinguished British physicist whose career has been devoted to the Cavendish Laboratory at Cambridge University, agreed to meet with MRS Bulletin at his home in Cambridge last fall. Sir Brian is a man whofollows his instincts without letting Convention Interrupt his path. Research grants were virtually unknown mid-century, so out of necessity he built his own research equipment to pursue his work. Later, he put his efforts toward educational reform in Cambridge, hitting a wall of indifference. While our agenda was to discuss physics and Sir Brian's contributions to materials Sci ence, the surroundings reminded us that his scientific contributions are balanced by a love of music. A piano sat beside us, and a music Stand served as a place to drape the microphone to capture his words. Once, this engineering construct failed, causing the microphone and stand to tumblefrom the coffee table to the floor, reminding us that every path has side trails and pitfalls, but one does not dwell therefor long. Sir Brian would rebut any Suggestion that he be termed a materials scientist, but his experiences carry lessons for us nonetheless. In 1956, he spent a period as a visiting professor at the Institute for the Study of Metals in Chicago and there he performed one ofthe key postwar experiments in solid-state physics, the determination of the shape of the Fermi surface in copper. He used as a tool the anom
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alous skin effect* at microwave frequencies, which is linked to the Fermi energy in different crystal directions. We asked him to teil us something about that year. Would you say, Brian, that your time in Chicago was really an application ofmetallurgical skills to the physical problem that you had set for yourself on why skin-effect measurements exposed geometrical results? That is exactly right. I had realized the year before, 1954 I think, that by doing measurements of the high-frequency skin effect on very pure metals with dean surfaces, one could get geometrical informa*The anomalous skin effect method involves applying a high-frequency field to a very pure Single crystal of metal at very low temperatures. The field induces currents in the metal, which tend to prevent penetration of the field into the specimen, limiting it to a certain "skin depth." At these low temperatures, the electron mean free path is much longer than the skin depth and only those electrons that run nearly parallel to the surface and within the skin depth remain in the field long enough to receive appreciable energy from the field. The effective resistance under these conditions is a function of the radius of curvature of the Fermi surface at those points that refer to electrons moving parallel to the surface; the anisotropy of the resistance for different crystallographic orientations can be used to test assumed modeis of the Fermi sur face and to determine its shape.
tion about the dynamics of the electrons in the metals. The shape of
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