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An essay on condensed matter physics in the twentieth century

W. Kohn
Rev. Modern Phys. 71, S59 (1999)

When the 20th century opened, the fields of crystallography, metallurgy, elasticity, magnetism, etc., dealing with diverse aspects of solid matter, were largely autonomous areas of science. Only in the 1940s were these and other fields consolidated into the newly named discipline of "solid state physics" which, two decades later, was enlarged to include the study of the physical properties of liquids and given the name "condensed matter physics" (CMP). At Harvard, for example, J. H. Van
Vleck had several times taught a graduate course on magnetism in the 1930s and 1940s. However, the first time a course called "solid state physics" was taught there was in 1949 (by the writer, at Van Vleck’s suggestion); it was based largely on the influential, comprehensive
monograph Modern Theory of Solids by F. Seitz, which had appeared in 1940. In the early 1950s only a handful of universities offered general courses on solids and only a small number of industrial and government
laboratories, most notably Bell Telephone Laboratories, conducted broad programs of research in CMP.
Today condensed matter physics is by far the largest subfield of physics. The writer estimates that at least a third of all American physicists identify themselves with CMP and with the closely related field of materials science. A look at the 1998 Bulletin of the March Meeting of the American Physical Society shows about 4500 papers in these fields.
Over the course of this century condensed matter physics has had a spectacular evolution, often by revolutionary steps, in three intertwined respects: new experimental discoveries and techniques of measurement;
control of the compositions and atomic configurations of materials; and new theoretical concepts and techniques. To give a brief and readable account of this evolution is immensely difficult due to CMP’s extraordinary diversity and many interconnections. Nevertheless, in the following pages the reader will find one theorist’s broadbrush—and necessarily very incomplete—attempt at this task. The writer (not a historian of science) had to make many difficult, often rather arbitrary, choices: how to organize this very short essay on a very broad subject
and—most painful—what to include and what important material to omit. He begs the reader’s indulgence.