arXiv subjects
Publications and source records attributed to Fedor V. Prigara.
It is shown that ferromagnetic ordering in metals is associated with an opening of the energy pseudogap. This energy pseudogap belongs to a d-band type in d-metals and to an sp-band type in f-metals. A relation between the magnetic energy and the Curie temperature is obtained. Effect of magnetic ordering on the temperature dependence of the electrical resistivity is considered.
It is shown that a structural transition in a metal is associated with the opening of the energy pseudogap in the electronic spectrum in a low-temperature phase below the transition temperature. A relation between the magnitude of the energy pseudogap in the d-band of transition metals (at zero temperature) and the structural transition temperature is similar to a relation between the magnitude of the superconducting gap and the superconducting transition temperature in low-temperature and high-temperature superconductors. A relation between the magnitude of the energy pseudogap and the structural transition temperature in sp-metals is similar to a relation between the bandgap width (at zero temperature) and the metal-insulator transition temperature in semiconductors.
It is shown that charge ordering in layered crystalline metals causes an increase in the normal state energy of the conducting layers. If this increase in the energy exceeds the difference between the superconducting state energy and the normal state energy of the metal, then the superconducting transition occurs. A relation between the charge gap in the superconducting phase and the bandgap width in the undoped insulating phase of high-temperature superconductors is obtained.
A relation between the energy of an elementary `insulating' excitation corresponding to the metal-insulator transition and the bandgap width in a semiconductor is obtained. An effect of atomic relaxation on the temperature and pressure dependence of the bandgap width is considered. It is shown that the metal-insulator transition in a semiconductor causes a weak rhombohedral or monoclinic distortion in the case of a diamond and zincblende structure and a weak tetragonal or orthorhombic distortion in the case of a rocksalt structure. A change in the bandgap associated with a ferroelectric (antiferroelectric) transition in a semiconductor is also obtained.
It is shown that a ferroelastic lattice distortion is associated with the superconducting transition both in low- and high-temperature superconductors. In layered tetragonal superconductors with a sufficiently high transition temperature, a ferroelastic distortion is improper and is caused by an out-of-plane charge ordering. The relation between the out-of-plane charge gap and the maximum superconducting transition temperature for these superconductors is obtained. It is shown also that the specific heat jump at the superconducting transition temperature in pnictide and cuprate superconductors is produced by ferroelastic fluctuations just below the transition temperature. The amplitude of the corresponding lattice distortion is estimated.
It is shown that the specific heat jump at the superconducting transition temperature in pnictide and cuprate superconductors is produced by ferroelastic fluctuations just below the transition temperature. The amplitude of the corresponding lattice distortion is estimated. It is shown that a contribution from ferroelastic fluctuations to the specific heat jump is also present in low-temperature superconductors.
The temperature dependence of the number density of elementary excitations in a semiconductor with account for the temperature dependence of the band gap is obtained. A local lattice distortion within a crystalline domain is discussed.
It is shown that a ferroelastic lattice distortion is associated with the superconducting transition both in low- and high-temperature superconductors. A low-temperature ferroelastic transition in crystalline solids produces also a maximum in the temperature dependence of their thermal conductivity. In layered tetragonal superconductors with a sufficiently high transition temperature, a ferroelastic distortion is improper and is caused by an out-of-plane charge ordering. The relation between the out-of-plane charge gap and the maximum superconducting transition temperature for these superconductors is obtained.
It is shown that a sufficiently strong external electric field causes a decrease in the transition temperature of ferroelectric, antiferroelectric, and metal-insulator transitions. The temperature dependence of the critical electric field suppressing a low-temperature phase is obtained. The relation between the low-temperature charge gap (the band gap) in the insulating phase and the metal-insulator transition temperature is also inferred.
Based on recent experimental results for electron-doped cuprate oxides and ferromagnetic superconductors, it is shown that antiferromagnetic fluctuations always develop in the superconducting phase of both low- and high-temperature superconductors. The relation between the magnitude of the antiferromagnetic pseudogap and the characteristic temperature of the antiferromagnetic pseudogap opening is obtained. The characteristic temperature of the antiferromagnetic pseudogap opening for metal superconductors is estimated.
Based on the formula for the number density of vacancies in a solid under the stress or tension, the model of grain boundary diffusion in crystalline solids is developed. We obtain the activation energy of grain boundary diffusion (dependent on the surface tension or the energy of the grain boundary) and also the distributions of vacancies and the diffusing species in the vicinity of the grain boundary.
The formula for the number density of vacancies in a solid under pressure is obtained. The mean number density of vacancies in a solid under stress or tension is also estimated. The dissolution of the vacancy gas in solids is shown to be responsible for the phases with composite incommensurate structures in metals under high pressure and also for the low values of the elastic limit and tensile strength of solids.
It is shown that the oscillations of brightness in classical Cepheids and other 'pulsating' variable stars are caused rather by the passing of radial solitary waves through the photosphere of a star, than by pulsations of a star. Radial solitary waves also determine the oscillations of brightness in some other types of periodic variable stars ordinary not considered as pulsating stars.
It is shown that the high- temperature phase transition in a plasma gives the mechanism of transition from the highly conductive state to the highly resistive state of a plasma in the `electric circuit' model of solar flares which was first introduced by H.Alfven and P.Carlqvist in 1967. With this addendum, the modern version of the electric circuit model can explain both the fast dissipation of energy and the acceleration of particles in a solar flare.
According to the recent revision of the theory of thermal radiation, thermal black-body radiation has an induced origin. We show that in single-bubble sonoluminescence thermal radiation is emitted by a spherical resonator, coincident with the sonoluminescing bubble itself, instead of the ensemble of elementary resonators emitting thermal black-body radiation in the case of open gaseous media. For a given wavelength, the diameter of the resonator is fixed, and this explains the very high constancy in phase of light flashes from the sonoluminesing bubble, which is better than the constancy of period of a driving acoustic wave.
The line of phase equilibrium between the hot and cold phases of a plasma is derived from the intensity of thermal radiation as a function of the plasma density and temperature. The last function is obtained with the help of the condition for emission relating the wavelength of radiation and the plasma density.
A transport barrier in a toroidal plasma is treated as the boundary region between the hot and cold phases of the plasma. These two phases possess essentially different collisional and transport properties, so the boundary region between them corresponds to the minimum values of specific resistivity and transport coefficients of the plasma. The behavior of magnetic shear in the region of a transport barrier and some other specific properties of transport barriers are the consequences of the minimum plasma resistivity in this region. The origin of sawtooth oscillations in toroidal plasmas is shown to have a similar nature.
It is shown that the existence of radiation-induced solitary waves in hot plasmas of accretion disks depends on the radial temperature profile.