Frenkel, Yakov Ilyich

Yakov Ilyich Frenkel (10.02.1894-23.01.1952) was a Soviet theoretical physicist and a corresponding member of the USSR Academy of Sciences (1929). He was born in Rostov-on-Don. He graduated from Petrograd University (1916). In 1918—21 he taught at the Crimean University. From 1921 he worked at the Leningrad Physico-Technical Institute (senior physicist, research supervisor, head of the theoretical department) and at the same time taught at the Polytechnic Institute, where for 30 years he headed the department of theoretical physics. His main work was in the field of solid-state physics, magnetism, the physics of liquids and nuclear physics. Applying quantum mechanics to the electron theory of metals, he was the first to formulate the basic concepts of the quantum theory of electrical conductivity and established the basic proposition of the modern electron theory, that the kinetic energy of the conduction electrons in metals is practically independent of temperature and is determined by quantum conditions. He gave a theory of the motion of atoms and ions in crystals, introduced the concept of defects of the crystal lattice, the “Frenkel defects” (1926), and the concept of mobile holes (hole conduction), and obtained a theoretical expression for the electrical conductivity of ionic crystals. In 1931 he developed a theory of the absorption of light by solid dielectrics and proposed the idea of excitons. He noted that tunnelling, as a quantum phenomenon, is responsible for the flow of current through a contact of two conductors separated by a thin insulating layer, and, independently of others, applied (1932) the notions of quantum-mechanical tunnelling to the treatment of rectification at a “metal — semiconductor” contact. He explained the nature of ferromagnetism, developing in 1928, independently of W. Heisenberg, the first quantum-mechanical theory of ferromagnetism, based on the exchange interaction between electrons (the collectivised model). In 1930, together with Ya. G. Dorfman, he gave the theory of the domain structure of ferromagnets. He introduced the notion of oscillatory-translational motion of molecules in liquids and constructed a kinetic theory of liquids. He extended the molecular theory of the fluidity of solids and the theory of diffusion and viscosity. He was the first to introduce (1936) the concept of the temperature of an excited atomic nucleus and the interpretation of its decay as the “evaporation” of particles from a “heated” nucleus. Independently of N. Bohr he developed in 1936 the liquid-drop model of the nucleus, and independently of him and of J. Wheeler he formulated in 1939 the foundations of the theory of the fission of heavy nuclei, predicting spontaneous fission. He also carried out a number of astrophysical, biophysical and geophysical studies. He developed the theory of a degenerate relativistic gas and applied it to the problem of the structure of stars, and calculated the limit for the mass of a stable star whose matter is in a degenerate state. He was the author of the first Russian courses of theoretical physics and published at various times “Statistical Mechanics”, “Electrodynamics”, “Wave Mechanics”, “A Course of Theoretical Mechanics Based on Vector and Tensor Analysis” and “The Kinetic Theory of Liquids” (USSR State Prize, 1947).