Физика низких температур, 2018, № 06
http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/150545
2024-08-14T10:11:10ZElastic phase transitions in solids. High pressure effect
http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/176171
Elastic phase transitions in solids. High pressure effect
Vekilov, Yu.Kh.; Krasilnikov, O.M.
At high pressures (the pressure is comparable with the bulk modulus) the crystalline lattice may become unstable relative to the uniform shear deformations, and in a result the low symmetric crystalline structures will appear (the so-called “elastic phase transitions”). The order parameters at these transitions are the components of the finite deformations tensor. The stability of the high-pressure phases is defined by the nonlinear elasticity of the lattice (the third, fourth etc. order elastic constants). Here the different cases of the stability loss at hydro-static pressure for the cubic structures are considered. The relation between the second, third and fourth order elastic constants is given, which defines the possibility of the first order deformation phase transition. The jump of the order parameter and the height of the potential barrier are defined by the third and fourth order elastic constants. As an example, the experimentally observed elastic phase transition in vanadium at P ≈ 69 GPa from bcc to the rhombohedral phase is analyzed, and the possible structural transitions in bcc Mo and W at P ≥ 700 GPa are also considered.
2018-01-01T00:00:00ZPhonon-kink scattering effect on the low-temperature thermal transport in solids
http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/176170
Phonon-kink scattering effect on the low-temperature thermal transport in solids
van Ostaay, J.A.M.; Mukhin, S.I.
We consider contribution to the phonon scattering, in the temperature range of 1 K, by the dislocation kinks pinned in the random stress fields in a crystal. The effect of electron-kink scattering on the thermal transport in the normal metals was considered much earlier [1]. The phonon thermal transport anomaly at low temperature was demonstrated by experiments in the deformed (bent) superconducting lead samples [2] and in helium-4 crystals [3,4] and was ascribed to the dislocation dynamics. Previously, we had discussed semi-qualitatively the phonon-kink scattering effects on the thermal conductivity of insulating crystals in a series of papers [5,6]. In this work it is demonstrated explicitly that exponent of the power low in the temperature dependence of the phonon thermal conductivity depends, due to kinks, on the distribution of the random elastic stresses in the crystal, that pin the kinks motion along the dislocation lines. We found that one of the random matrix distributions of the well known Wigner–Dyson theory is most suitable to fit the lead samples experimental data [2]. We also demonstrate that depending on the distribution function of the oscillation frequencies of the kinks, the power low-temperature dependences of the phonon thermal conductivity, in principle, may possess exponents in the range of 2–5.
2018-01-01T00:00:00ZOn the theory of the Schrödinger equation with the full set of relativistic corrections
http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/176169
On the theory of the Schrödinger equation with the full set of relativistic corrections
Eremko, A.A.; Brizhik, L.S.; Loktev, V.M.
All relativistic corrections to the Scrödinger equation which determine the interlink between spin and orbit of moving particles, are directly calculated from the Dirac equation using the spin invariant operators. It is shown that among the second order corrections there are not only the well-known Darwin and Thomas terms, but also the new ones. Only with the account of the latter corrections the energies found with the obtained spin-orbit interaction operator, coincide with the energies of the Dirac equation exact solution. The problem of electron spectrum in the quantum well type structures is studied in details and the physical reasons for the appearance of spin-orbit interaction operators in the Dresselhaus or Rashba form, are analyzed.
2018-01-01T00:00:00ZOscillations of magnetization in topological line-node semimetals
http://dspace.nbuv.gov.ua:80/xmlui/handle/123456789/176168
Oscillations of magnetization in topological line-node semimetals
Mikitik, G.P.; Sharlai, Yu.V.
We theoretically investigate the phase of the de Haas–van Alphen oscillations in topological line-node semimetals. In these semimetals the chemical potential of charge carriers can essentially depend on the magnetic field, and this dependence changes the phase of the oscillations as compared to the phase in a three-dimensional metal with a band-contact line. Our results elucidate recent experimental data on the Berry phase for certain electron orbits in ZrSiS, ZrSiTe, and ZrSiSe.
2018-01-01T00:00:00Z