Based on the equations of electrodynamics and the concept of a critical state for hard superconductors of the 2nd kind, numerical simulation of the magnetic properties of axisymmetric superconducting samples, in particular, granules, is performed for a number of models of the dependence of the critical current density on the magnetic field induction. The magnetic moment loops are calculated directly by integrating the integral equation for the current density over time. The phenomena of the peak effect and the asymmetry of the magnetization hysteresis loop are also considered using the indicated equation. Various versions of the functions used in the literature were used as peak functions. In addition to the hysteresis loop of the magnetic moment, the magnetic field induction at the center of axisymmetric samples, and the total penetration field, the profiles of the critical current density Jc(B) and the equilibrium magnetic moment for spherical granules were obtained. The method used for calculating the magnetic moment of superconductors makes it possible to take into account the equilibrium and nonequilibrium regions of the magnetization of the samples independently.
Using time sweeps of the current through a sample of a superconducting film, the effect of the current sweep rate on the process of heat propagation from current contacts is investigated. The samples used were NbN films located below and above the transition temperature to the superconducting state. A method for determining the critical heating of key zones of the sample is proposed. The propagation velocities of the resistive front and normal domain in a superconductor are estimated at different temperatures.
Исследовано влияние тока и магнитного поля на переход в сверхпроводящее состояние в тонких пленках нитрида ниобия. Определены температурные и магнитополевые зависимости критического тока пленок в области перехода. В рамках моделей нормального домена и разогрева квазичастиц при вязком течении магнитного потока найдены функциональные зависимости критического тока в непосредственной близости к температуре перехода в сверхпроводящее состояние. Из теории разогрева электронов определено время их энергетической релаксации. Оценены время электрон-фононного и электрон-электронного неупругого рассеяний, коэффициент диффузии электронов, коэффициент теплоотвода.
A sequence of inhomogeneous differential equations for reconstructing the derivative of the nonlinear current–voltage characteristic is studied. The right-hand side of these equations is the experimentally determined dependence of the first-harmonic voltage on direct current. Such voltage arises, e.g., at the output of a nonlinear semiconductor structure simultaneously exposed to alternating and direct current. Based on numerical solutions of differential equations, the developed technique is applied to reconstruct the derivative of the current–voltage characteristic of two antiparallel connected p – n junctions.
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