A theory is developed for structural phase transitions in the layer metallic compound 1 T-VSe 2 , taking into account the interlayer interaction of charge density waves (CDWs). Three-dimensional ordering of CDWs is investigated, and with information about the strength of diffuse x-ray scattering a conclusion is drawn regarding the structure of the incommensurate phases
Neutron diffraction by polycrystalline samples was used to determine the magnetic order in Re 2 BaCuO 5 cuprates, where Re = Dy, Ho, Er, Tm, and Yb. The investigation was carried out at various temperatures. The crystal structure parameters were determined in the paramagnetic phase. All the compounds exhibited different antiferromagnetic structures. Spin-reorientation transitions were observed for Dy 2 BaCuO 5 and Ho 2 BaCuO 5 when temperature was varied
The lattice reflection spectra of Cd 1−x Hg x Te alloys are analyzed in the two-mode approximation for the vibrational spectrum of quasibinary alloys in terms of CdTe- and HgTe-like vibrations. The composition dependences of frequencies of the TO and LO modes of CdTe-like and HgTe-like vibrations are obtained at temperatures 25, 85, and 300 K. A comparison is made of the information derived from the two-mode and quasimolecular approximations
An investigation is reported of static and dynamic optical bistability and optical switching in a system of coherent excitons and biexcitons in semiconductors subject to the exciton-photon interaction and optical conversion of excitons into biexcitons. The Heisenberg equations of motion for excitons and biexcitons and the wave equation for the field are used to derive a system of nonlinear differential equations describing the dynamic evolution of such a system. The equation of state for a theory of optical bistability is derived for the static case. A study is made of the stability of stationary optical bistability states. A computer experiment is used in an investigation of the switching times between the branches
An investigation was made of the influence of uniaxial compression of a sample along the principal magnetic axis of one of three geometrically inequivalent Jahn-Teller Cu 2+ -ion centers in a single crystal of zinc fluorozirconate on the ESR spectrum. Calculations were made of the deformation coefficient V ES =#752420 cm #751 , of the Jahn-Teller energy E JT = 1140 cm #751 , and of the linear vibronic interaction constant V=#752.09×10 #755 erg/cm. An analysis was also made of the experimental investigations of trigonal hydrated crystals. The role of the dynamics of the nuclear core in determination of the properties of a Jahn-Teller center was demonstrated
It is proposed to used, as a basic property specifying the difference between an insulator and a conductor, a static phenomenon, namely the field effect which absent in the former, but present in the latter. The absence or present of the field effect is closely associated with the nature of the homogenious linear response to a static electric field. For an insulator, it is finite; for a conductor, it depends on the volume V and tends to infinity when V to infinity. The fluctuation-dissipation theorem makes it possibile to relate the nature of this response to the mean square fluctuation of the dipole moment of the system, which is normal in an insulator, but anomalious in a conductor. A number of examples are considered. A notable property of the BCS supercondctivity state have remarked, namely: its conductivity property is a consequence of non-zero electron density fluctuations in the ground state of the system with ODLRO.
An investigation was made of the influence of uniaxial compression of a sample along the principal magnetic axis of one of three geometrically inequivalent Jahn-Teller Cu 2+ -ion centers in a single crystal of zinc fluorozirconate on the ESR spectrum. Calculations were made of the deformation coefficient V ES =#752420 cm #751 , of the Jahn-Teller energy E JT = 1140 cm #751 , and of the linear vibronic interaction constant V=#752.09×10 #755 erg/cm. An analysis was also made of the experimental investigations of trigonal hydrated crystals. The role of the dynamics of the nuclear core in determination of the properties of a Jahn-Teller center was demonstrated
The three-crystal x-ray diffractometry method was used in an investigation of clean cleaved surfaces of ferroelastic CsDSO 4 and ferroelectric CsH 2 PO 4 crystals immediately after cleaving, after several days of storage in an atmosphere of dry nitrogen, and after low-temperature annealing at 80 °C. These crystals were of fairly high quality with the dislocation density in the range 8×10 4 -3×10 5 cm -2 in the surface layers. In the case of CsDSO 4 this density depended on the duration of storage and on the annealing procedure
It is shown that the geometric relationships between the lattices of cubic γ-uranium and orthorhombic α-uranium can be derived in a model of reorientable nonspherical atoms. The use of this model to explain qualitatively the anomalous relationship between the thermal expansion coefficients is discussed; it is in accordance with the properties of solid solutions and the magnetic properties of uranium chalcogenides
