arXiv subjects

G. F. Zharkov

Publications and source records attributed to G. F. Zharkov.

6 recordsLinked to original sources

arXiv2002

First and second order phase transitions and magnetic hysteresis for a superconducting plate

The self-consistent solutions of a nonlinear Ginzburg--Landau equations, which describe the behavior of a superconducting plate of thickness 2D in a magnetic field H parallel to its surface (provided that there are no vortices inside the plate), are studied. We distinguish two types of superconductors according to the behavior of their magnetization M(H) in an increasing field. The magnetization can vanish either by a first order phase transition (type-I superconductors), or by a second order (type-II). The boundary S_{I-II}, which separates two regions (I and II) on the plane of variables (D,kappa), is found. The boundary zeta(D,kappa) of the region, where the hysteresis in a decreasing field is possible (for superconductors of both type), is also calculated. The metastable d-states, which are responsible for the hysteresis in type-II superconductors, are described. The region of parameters (D,kappa) for type-I superconductors is found, where the supercooled normal metal (before passing to a superconducting Meissner state) goes over into a metastable precursor state (p-). In the limit kappa --> 1/sqrt{2} and D>>lambda (where lambda is the London penetration depth) the self-consistent p-solution coincides with the analytic solution, found from the degenerate Bogomolnyi equations. The critical fields H_1, H_2, H_p, H_r for type-I and type-II superconducting plates are also found.

cond-mat.supr-con↗

arXiv2001

Onset of superconductivity and hysteresis in magnetic field for a long cylinder as obtained from a self-consistent solutions of the Ginzburg--Landau equations

Based on the self-consistent solution of a nonlinear system of one-dimensional GL-equations, the onset and destruction of superconductivity, the phase transitions and hysteresis phenomena are discussed for a cylinder (radius R) in an axial magnetic field (H) for arbitrary R,kappa,H,m (kappa$ is the GL-parameter, m is the total vorticity of the system). The edge-suppressed solutions (which are connected with the jumps of magnetization in the states with fixed vorticity m), the depressed solutions (responsible for the hysteresis in type-II superconductors), and the precursor solutions (which describe the onset of superconductivity in type-I superconductors) are also studied. The limits of applicability of the so-called linear equation approximation are discussed.

cond-mat.supr-con↗

arXiv2000

Transitions of I- and II-order in magnetic field for superconducting cylinder from self-consistent solution of Ginzburg-Landau equations

Basing on self-consistent solution of non-linear GL-equations, the phase boundary is found, which divides the regions of I- and II-order phase transitions of a superconducting cylinder in magnetic field to normal state. This boundary is a complicated function of the parameters (m,R,kappa) (m is the vorticity, R is the cylinder radius, kappa is the GL-parameter), which does not coincide with the simple phase boundary kappa=1/\sqrt{2}, dividing the regions of I- and II-order phase transitions in infinite (open) superconducting systems.

cond-mat.supr-con↗

arXiv2000

Paramagnetic Meissner effect in superconductors from self-consistent solutions of Ginzburg-Landau equations

The paramagnetic Meissner effect (PME) is observed in small superconducting samples, and a number of controversial explanations of this effect are proposed, but there is as yet no clear understanding of its nature. In the present paper PME is considered on the base of the Ginzburg-Landau theory (GL). The one-dimensional solutions are obtained in a model case of a long superconducting cylinder for different cylinder radii R, the GL-parameters κand vorticities m. Acording to GL-theory, PME is caused by the presence of vortices inside the sample. The superconducting current flows around the vortex to screeen the vortex own field from the bulk of the sample. Another current flows at the boundary to screen the external field H from entering the sample. These screening currents flow in opposite directions and contribute with opposite signs to the total magnetic moment (or magnetization) of the sample. Depending on H, the total magnetization M may be either negative (diamagnetism), or positive (paramagnetism). A very complicated saw-like dependence M(H) (and other characteristics), which are obtained on the base of self-consistent solutions of the GL-equations, are discussed.

cond-mat.supr-con↗

arXiv2000

Self-consistent solutions of Ginzburg-Landau equations and superconducting edge-suppressed states in magnetic field

Self-consistent solutions of the Ginzburg-Landau system of equations, which describe the order parameter and the magnetic field distribution in a long superconducting cylinder of finite radius R, in external magnetic field H, when vortex line, carrying m flux quanta, is situated on the cylinder axis (a giant m-vortex state), are studied numerically. If the field H exceeds some critical value H_s, the giant m-vortex solution becomes unstable and passes to a new stable edge-suppressed form. The quantum number m in this state does not change, but the order parameter diminishes by a jump (almost to zero) near the cylinder surface; however, superconductivity remains in the deep, at some distance from a cylinder axis. This edge-suppressed state exist in the fields H_s 1/sqrt{2}). The paramagnetic effect in mesoscopic samples and also the possible connection of the theory and experiment are shortly discussed.

cond-mat.supr-con↗

arXiv1997

Type I Superconductivity in Neutron Stars

The magnetic structure of neutron vortices in the superfluid cores of neutron stars is determined assuming that the proton condensate forms a type I superconductor. It is shown that the entrainment currents induced by the neutron vortex circulation cause the proton superconductor to break into successive domains of normal and superconducting regions. The Gibbs free-energy is found in the case in which the normal domains form cylindrical tubes coaxial with the neutron vortex. The minimum of the energy functional corresponds to a tube radius $a\sim 0.1-0.5 ~b$, where $b$ is the outer radius of the neutron vortex. The magnetic field within the tube is of the order of $ 5 \times 10^{14}$ G.

astro-ph↗