Biographical Memoirs Volume 56 (1987) / Chapter Skim
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John Hasbrouck Van Vleck
John Hasbrouck Van Vleck
Pages 500-541
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W ANDERSON JOHN HASBROUCK VAN VLECK was the most eminent American theoretical physicist between }.
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Hester Raymond of MidcIletown in IS93, ant! here John Hasbrouck Van VIeck, his only chilcI, was born on March 13, TS99.
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His youthful preference tract been not to go into the academic life, and he recordecI in his reminiscences that "serious young men took engineering rather than math or physics, where most of the students were girls." Just as he rebelled at solving triangles graphically, he evacled the physics senior thesis involving experimental work, including, worst of all possible fates, glassblowing by joining a debating team ant! arguing successfully against the government ownership of railroads.
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Van's interest enormously. In the next year he took a course from Professor March on dynamics that was his introduction to genuine theoretical physics and showed him very clearly the course of his future career.
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In short orcler there followed a sequence of papers on various aspects of spectroscopy using the old quantum theory, and then a book, Quantum Principles and Line Spectra, finished in late 1925. During the Harvard years, Van was in constant touch with John Slater, who finished a mostly experimental thesis with Bridgman at about the same time, and then left for Copenhagen to work for a year with Bohr.
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It was well received, but by the time it was issued in early 1926 much of it had been supersecled by the enormous explosion of results from the new quantum mechanics. The exercise, however, was of considerable value
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was to set the theme for much of the rest of his career: the use of the new quantum mechanics to elucidate electromagnetic properties of matter. This had been an interest of his since an early seminar on the Weiss theory of ferromagnetism, and it was implicit in his correspondence principle paper; but from now on his interest led to a stream of fundamental papers, and it became clear that he hacI chosen this as his particular portion of the great work of verifying and using the new quantum theory.
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other spectra in the new mechanics that was a second major theme in his life with a paper with Hill on rotational distortion tI61. He was asked by the chemists to review the new quantum mechanics Ll7]
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1 ~ fit in materials, of Heisenberg's tneory ot terromagnet~sm, ot aspects of ctielectric local fields and of dielectric theory in general, of Landau diamagnetism and its relationship to the classical theory, and the like. It is marked perhaps even slightly marred, as a modern text for physicists poorly trained in classical mechanics by careful discussion of the ways in which quantum mechanics, the old quantum theory, and classical physics differ.
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The orbital angular momentum in most iron group ions in solicls is "quenched" (a typical Van concept) by such fields, because of the weakness of spin-orbit coupling relative to the crystal field splittings, while rare earth ions retain free ion character but responc!
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The former stimulatect several of the papers aIreacly quoted, as well as t504; the latter led to Van's remarkable anc! prescient calculations of the paramagnetic relaxation caused by lattice modulation of the crystal field parameters ~ t59]
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Van particularly enjoyed trying to reconcile opposing schools of thought on the important questions. As I remarkect, he actually originated both schools in the case of crystal and ligand field theory.
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. He contributed to questions of the interpretation of quantum mechanics (id]
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This was even more true of postdoctoral associates; he brought John Bardeen and Nico Bloembergen to Harvard as junior fellows, as well as many visitors in other capacities, such as Broer, Van Kranendonk, Gorter, Abragam, and others with whom his name is not usually closely linked. HARVARD: WAR AND IMMEDIATE POSTWAR YEARS VAN AS CONSULTANT, GREY EMINENCE, AND MIDWIFE TO THE BIRTH OF QUANTUM ELECTRONICS Although Van continued some teaching at least through 1943, he carried out several roles, especially that of head of the theory group (after 1942)
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Felix Bloch (~7311; a classic and technologically vital pair of reports on identifying pulses in the presence of noise, carried out with David Midclleton (~7214; an(l, particularly, his (1iscovery that the ill-fated "K-bancI" racier operating at A = 1.25 cm would be a fiasco because of atmosphere absorption by molecular lines of O2 and, particularly, water. In order to work out this conclusion quantitatively it was necessary to revise accepted theories of collision broadening (since the relevant lines wouIct be severely broadenecl)
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. At the same time he maintained close rapport with the Leyclen group, which was pushing relaxation spectroscopy up in frequency from the radiofrequency end, culminating in Gorter's work cluring the war and shortly after, and which was the most technically close (because of its emphasis on line-width and relaxation, as well as its instrumentation)
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In essence, this fielcI can be clefinect as the physics of the interaction of coherent electromagnetic radiation with atomic, molecular, or solid-state systems of quantized energy levels. The first step, of course, is the mental leap of recognizing that suitable systems of energy levels exist in reasonable profusion, and with energy level breadths that do not overwhelm the quantization of the levels and leave one with a featureless classical smear.
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What Van and he wanted to do was to strike a mictdle ground between the free-electron theory purists, especially Stoner, who were determiner! to apply the pure Bloch band theory of ferromagnetism and ignore the necessarily strong electronic interactions otherwise; and the naive "Heisenberg moclel" theorists who proposes]
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He was closely associated with the work of the APS, and Bill Havens, the present secretary, remembers his help with much gratitude, both at that time and later. As chairman of the Physics Department, Van presided over the admission-and recruitment of an extraordinary group of students in the first few years, brought back at irregular times and from the ends of the earth, mixing refugees, returning servicemen, and bright young products of the wartime accelerated courses.
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One of his stratagems in cloing this was the "Van VIeck Bridge," an actual physical connection between Cruft Laboratory, where many of the applied scientists were, and the Jefferson Physics Lab. After six years as dean, Van returned in 1957 to more or less private academic life, although first he server} as vice president of the IUPAP, 1958-60, anc!
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. Other rare earth materials discussed includecl euro pium metal ~ ~ ~ 41; Sm intermetallic compounds ~ ~ ~ X]
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, (where he kindly publicized my own early work) ; rare earth magnetism tI373; and line breadths (with David Huber, his last contribution of some ten or more to Reviews of Modern Physics, tI6734.
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widely respected particle theorist; an eminent plasma theorist; and a Nobel prizewinner. Just as Van wrote the first American thesis on the old quantum theory, his student E
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Second, he supplied a "crib" for examination study, which we always thought was practically cheating, saying precisely what couIct
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Several of his lecture note sets the Henri Poincare in 1939, and Varenna in 1957, for instance are important scientifically. As time went on he was increasingly in demancl for semi-ceremonial speeches, anc!
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Lorentz meclal, 1974; Chevalier of the Legion (l'Honneur, 1970; foreign membership in The Royal Society; and finally the Nobel prize. Aside from an operation, he remained in good health until about 1975, when he began to have a heart weakness that required a pacemaker.
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B Van VIeck Hall at Madison, Van quoted his father's precepts: "Two qualities may be noticed as especially needed by the American Escientist]
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1927 F10] On dielectric constants and magnetic susceptibilities in the new quantum mechanics, Part I
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USA, 14: 178-88. On dielectric constants and magnetic susceptibilities in the new quantum mechanics, Part III.
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Phys., 2:297-98. A new method of calculating the mean value of 1/rS for Keplerian systems in quantum mechanics.
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1938 L52] L501 On the adiabatic demagnetization of cesium titanium alum.
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On the energy levels of chrome alum.
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Collision theories of pressure broadening of spectral lines.
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Improved theory of the Zeeman effect of atomic oxygen.
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Chem., 16:358-67. t1081 The magnetic behaviour of regular and inverted crystalline energy levels.
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1962 F1231 Exchange fields in rare earth iron garnets.
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L1391 Note on the crystal field parameters of rare earth garnets.
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1967 L1421 The evolution of crystal field parameters for rare earth salts. In: Interaction of Radiation with Solids, pp.
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Theory of the magnetic anisotropy and nuclear magnetic resonance of europium iron garnet.
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Phys., 49:939-49. 1978 L1681 Quantum mechanics: The key to understanding magnetism.
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