The properties of magnetic insulators containing orbitally degenerate transition metal ions (Jahn-Teller ions) are discussed. The Jahn-Teller effect in these insulators causes structural phase transitions, lowers the lattice symmetry, and gives rise to an orbital ordering. Various interactions responsible for these effects are discussed: the electron-lattice, quadrupole-quadrupole, and exchange interactions. The mutual effects of the orbital ordering and the magnetic properties of corresponding compounds are discussed. The exchange interaction in the cases of twofold and threefold orbital degeneracy is discussed. The effect of a magnetic field on the orbital and magnetic structure and the temperature dependence of the exchange interaction are studied. The properties of several representative compounds containing Jahn-Teller ions are discussed.
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Viktor G Veselago 1968 Sov. Phys. Usp. 10 509
Kliment I Kugel' and D I Khomskiĭ 1982 Sov. Phys. Usp. 25 231
V I Belinicher and B I Sturman 1980 Sov. Phys. Usp. 23 199
This review presents the fundamental theoretical concepts concerning the photogalvanic effect (PGE)—the phenomenon of appearance of a direct current in a homogeneous medium under uniform illumination. This effect can occur in all media lacking a center of symmetry, in particular, in ferroelectrics, piezoelectrics, gyrotropic crystals, and in gases and liquid possessing natural optical activity. The starting point of a systematic microscopic theory is the asymmetry of the elementary electronic processes—their noninvariance with respect to spatial reflection. Within the framework of the theory, we study the most important mechanisms of the PGE in the regions of impurity, interband, and intraband light absorption. Possible observable manifestations of the PGE are discussed. Theoretical results are compared with experimental data.
A S Davydov 1964 Sov. Phys. Usp. 7 145
A I Vaĭnshteĭn et al 1982 Sov. Phys. Usp. 25 195
An attempt is made to present an instanton "calculus" in a relatively simple form. The physical meaning of instantons is explained by the example of the quantum-mechanical problem of energy levels in a two-humped potential. The nonstandard solution to this problem based on instantons is analyzed, and the reader is acquainted with the main technical elements used in this approach. Instantons in quantum chromodynamics are then considered. The Euclidean formulation of the theory is described. Classical solutions of the field equations (the Belavin–Polyakov–Shvarts–Tyapkin instantons) are obtained explicitly and their properties are studied. The calculation of the instanton density is described and the complete result is given for an arbitrary number of colors. The effects associated with fermion fields are briefly described.
A M Perelomov 1977 Sov. Phys. Usp. 20 703
The review is devoted to an analysis of definite overcomplete non-orthogonal state systems that are connected with irreducible representations of Lie groups–the so called systems of generalized coherent states. These systems, which the author is the first to propose, are generalizations of Glauber's coherentstate system and arise in natural fashion in physical problems that have dynamic symmetry. They permit a considerable simplification of the solution of the quantum problem by reducing it to a simpler "classical" problem. The review deals with the properties of generalized-coherent-state systems connected with the simplest Lie groups.
A P Levanyuk and Daniil G Sannikov 1974 Sov. Phys. Usp. 17 199
Improper ferroelectrics are considered in the review from a unified point of view on the basis of the phenomenological Landau theory of phase transitions. In such ferroelectrics, in contrast to the ordinary ones, the order parameter of the phase transition is not the polarization but another physical quantitiy whose transformation properties are different from those of the polarization. Spontaneous polarization arises in the phase transition as a secondary effect. Therefore, the dielectric anomalies in the improper ferroelectrics are significantly different from the dielectric anomalies in the ordinary ferroelectrics. In particular, the temperature dependence of the permittivity does not obey the Curie-Weiss law, an electric field does not suppress the phase transition, etc. The dielectric anomalies are derived by analyzing a definite form of the thermodynamic potential with a two-component order parameter. Such an analysis turns out to be sufficient for the discussion of the available experimental data. The domain structure of the improper ferroelectrics also possesses specific properties: In particular, there exist domains which do not differ in their polarizations. Since the loss of stability in an improper ferroelectric phase transition occurs not with respect to polarization, the soft mode in the nonpolar phase is inactive in the infrared spectrum. Other distinctive features of the phonon spectrum in the phase-transition region are also considered. The experimental data on improper ferroelectrics are discussed. For the rare-earth molybdates, the theory is in quantitative agreeement with experiment. In certain other improper ferroelectrics the phase transitions are of first order and nowhere near to being of second order. The quantitative description of such transitions requires additional experimental data and further development of the theory.
R N Gurzhi 1968 Sov. Phys. Usp. 11 255
Introduction I. Kinetic Phenomena in Dielectrics 256 1. Statement of the Problem 256 2. Hydrodynamic Mechanism of Thermal Conductivity 257 3. Influence of Higher-order Anharmonicity on Transfer Processes in Solids at Low Temperatures 259 4. Second Sound in Dielectrics 260 II. Kinetic Phenomena in Metals 5. Electrical Conductivity of Metals at Low Temperatures 262 6. Electrical Conductivity of Thin Samples 264 7. Electrical Conductivity of Bulk Samples 266 8. High-frequency Properties 268 References 269
L A Fal'kovskiĭ 1968 Sov. Phys. Usp. 11 1
CONTENTS Introduction 1 I. Space Lattice 2 II. Doubling of the Period 2 III. Electron Energy Spectrum 4 1. Expansion Near Extremum 4 2. Two-band Model 4 3. Deformation Theory 6 IV. Electron Spectrum in a Constant Magnetic Field 8 1. Classical Limit 8 2. Two-band Model and Extremum of Band 9 3. Quasiclassical Quantization 9 V. Specific Heat 10 VI. Magnetic Susceptibility 10 VII. Quantum Oscillations of the Susceptibility and of Other Thermodynamic and Kinetic Quantities 11 VIII. Electric Conductivity 14 1. Static Conductivity in a Constant Magnetic Field 14 2. Conductivity in the Absence of Constant Magnetic Field 14 3. Cyclotron Resonance 15 4. Magnetoplasma Waves 17 5. Optical Properties in the Infrared Region 19 IX. Measurement of the Fermi Momenta in Experiments with Ultrasound and by Determining the Cutoff of the Cyclotron Resonance 20 X. Tunnel Effect 20 XI. Phonon Spectrum 20 XII. Cited Literature 20
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Valerii I Klyatskin and Aleksandr I Saichev 1992 Sov. Phys. Usp. 35 1096
Ya A Smorodinskiĭ et al 1992 Sov. Phys. Usp. 35 1005
The current state of the foundations of quantum mechanics is discussed. The analysis takes as its starting point the theory of probability amplitudes, which is intimately related to the group-theoretic approach. A detailed examination is presented of the relationships of classical and quantum theories, the transition to the classical limit, the different forms of uncertainty relations, and the properties of quantum structures determined by the Clebsch–Gordan coefficients. Possible future generalizations are examined, including those involving quantum algebras.
Alexander A Kolokolov and G V Skrotskiĭ 1992 Sov. Phys. Usp. 35 1089
This article discusses the formation of an interference energy flux as a result of changing the phase shift between the oscillations of the reactive components of the vectors of the electric and magnetic field intensities of radiation when spatially superposed. On the basis of a model of the interference of the reactive components of the electromagnetic field from a common physical standpoint, the passage of light through a transparent plane-parallel plate at an angle of incidence exceeding the critical angle of total internal reflection, the formation of a refracted wave in the region of total internal reflection from a semiinfinite medium, and the radiationless transport of energy between excited and unexcited atoms are described.
Boris M Smirnov 1992 Sov. Phys. Usp. 35 1052
The properties of systems consisting of classical atoms with a short-range interaction and the processes occurring in them are studied. An asymptotic theory is presented for the transport coefficients and other parameters of a gas, which exploits the steepness of the interaction potential of the atoms in the repulsive region. A comparison of the parameters of various condensed inert gases shows that these parameters can be expressed in terms of the interaction potential between two atoms. On the basis of a model of close-packing of the atoms analyses are made of the properties of large clusters, the surface energy of condensed and porous systems, the surface tension of liquids and liquid metals, and of the solid-liquid phase transition.
Anatolii K Zvezdin et al 1992 Sov. Phys. Usp. 35 1080
Review articles
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Ya A Smorodinskiĭ et al 1992 Sov. Phys. Usp. 35 1005
The current state of the foundations of quantum mechanics is discussed. The analysis takes as its starting point the theory of probability amplitudes, which is intimately related to the group-theoretic approach. A detailed examination is presented of the relationships of classical and quantum theories, the transition to the classical limit, the different forms of uncertainty relations, and the properties of quantum structures determined by the Clebsch–Gordan coefficients. Possible future generalizations are examined, including those involving quantum algebras.
Boris M Smirnov 1992 Sov. Phys. Usp. 35 1052
The properties of systems consisting of classical atoms with a short-range interaction and the processes occurring in them are studied. An asymptotic theory is presented for the transport coefficients and other parameters of a gas, which exploits the steepness of the interaction potential of the atoms in the repulsive region. A comparison of the parameters of various condensed inert gases shows that these parameters can be expressed in terms of the interaction potential between two atoms. On the basis of a model of close-packing of the atoms analyses are made of the properties of large clusters, the surface energy of condensed and porous systems, the surface tension of liquids and liquid metals, and of the solid-liquid phase transition.
Aleksei I Osipov and A V Uvarov 1992 Sov. Phys. Usp. 35 903
We review the propagation of optical and hydrodynamic perturbations in a gas having nonequilibrium internal degrees of freedom. We discuss the nonequilibrium processes that lead to variation of the refractive index and self-focusing via the effect of kinetic cooling and nonequilibrium vibrational excitation of molecules. We analyze the propagation of small and nonlinear perturbations, as well as shock waves, in nonequilibrium gases.
M B Gitis 1992 Sov. Phys. Usp. 35 924
The linear long-wave approximation is used to analyze the classical interaction between elastic waves and local disorder in dielectric, semiconducting, and metallic crystals. It is shown that carriers of thermal and nonthermal disorder provide significantly different contributions to the acoustic parameters of crystals such as the velocity of sound and the sound attenuation coefficient. The effect of direct and indirect interactions between elastic waves and the ensemble of carriers of disorder on the attenuation of sound is examined. In the former case, deformation by the wave modifies the motion of the carriers of disorder themselves, whereas in the latter case the elastic wave interacts with quasiparticles in the crystal, and the presence of disorder is seen as a change in the character of motion of these quasiparticles. The effects of high concentrations of carriers of disorder produced by melting one of the sublattices of superionic crystals are also described.
M B Gitis 1992 Sov. Phys. Usp. 35 956
Manifestations of order in topologically disordered media are analyzed. Amorphous materials and monatomic melts are considered as examples of disordered media. It is shown that in the case of close-packed liquids geometric and chemical short-range order are most clearly manifested in the acoustic properties. In these materials ordering is of a dynamical character. The temperature dependence of the acoustic properties correlates well with the results of x-ray and neutron diffraction methods of investigation and substantially supplements the latter. The contributions from loss of long-range order and intensification of thermal translational motion on melting are distinguished from one another by comparing the bulk moduli of elasticity of melts, crystals, and amorphous substances.