B. Ya. Shapiro

Relaxation of magnetic flux in a superconductor with a system of columnar defects

Abstract The interaction of Abrikosov vortices with columnar defects (with single defects and with a periodical structure) is considered. It is shown that interdefect regions can play the role of pinning centers because of the existence of a potential barrier for vortices. The energy barrier and the magnetic relaxation rate as a function of temperature are calculated. A step-like behavior of the magnetic relaxation rate in a high magnetic field is predicted.

The transition temperature and critical magnetic field of the localized superconductive states for space-inhomogeneous superconductors

Abstract A theory of the proximity effects in the inhomogeneous dirty superconductors has been developed. The critical magnetic field as a function of temperature and of the length of the inhomogeneity has been investigated. The angular dependence has been obtained.

Effect of the surface roughness on Bean-Livingston surface barrier

Abstract Bean-Livingston barrier for a single Abrikosov vortex interacting with the rough surface is calculated as a function of the random characteristics of the surface roughness. It has been shown that even a respectively smooth surface roughness results in an essential decrease of the Bean-Livingston surface barrier.

The critical parameters and structure of the surface superconducting state induced by external electric field

Abstract Electric field perpendicular to a surface of superconducting semiconductor or semimetal induces superconducting transition at temperature and in magnetic field higher than in the bulk. The magnetic moment and structure of the inhomogeneous surface superconducting state are calculated. All parameters depend on direction of magnetic field, magnitude of electric field, and temperature.

Proximity effects in inhomogeneous superconductors

A theory of the proximity effect in inhomogeneous dirty and pure superconductors is presented. We have obtained the critical magnetic field as a function of temperature and of the characteristic length of the inhomogeneity. The angular dependence of the critical magnetic field has also been investigated. We have obtained the critical magnetic field for plane, linear, and local inhomogeneities. The theory is based upon microscopic equations of superconductivity.

Periodic negative magnetoresistance in granular YBa2Cu3O7−δ nanowires

Magneto-transport measurements in YBa2Cu3O7−δ nanowires, comprising a single layer of a small number of grains, reveal periodic magnetoresistance oscillations in a wide temperature range below the transition. The rich structure of these oscillations manifests a negative magnetoresistance in the initial part of each cycle beginning at zero magnetic field. The salient features of these unique oscillations indicate the presence of π Josephson junctions in the granular wires, arising from the d-wave pairing symmetry in YBa2Cu3O7−δ.

The transverse optical mode and high temperature superconductivity

Abstract A theory of superconductivity is proposed taking into account the interaction of the holes with the transverse optical modes. The critical temperature is obtained in the framework of the two-band model. The dependence of the critical temperature on the concentration of the oxygen defects in the Cu-O chains is discussed.

Voltage noise due to randomly interrupted motion of vortices

The voltage noise generated by an randomly interrupted flow of flux vortices across thin film superconducting strips is discussed. It is demonstrated that processes of vortex pinning and depinning, as well as motion of vortex-density fluctuations contribute to the noise spectra. Random switching of vortices between the state of pinning and flow results in random telegraph noise-like behavior at high frequencies. The flow of spatially non-correlated vortices, or vortex bundles, results in oscillatory peaks in the power spectra. The difference in frequency between two peaks is related to the inverse of the average time the vortices need to cross the sample. The shape of the voltage noise spectrum dramatically depends on the ratio of average lifetimes of vortices in the pinned and in the flow state. Spectral oscillations are attenuated and disappear with increasing pinning strength. It is demonstrated that the physical picture depends on the type of geometrical resolution function chosen for the calculations.

Surface superconductivity induced by an external electric field

Abstract A theory of surface superconductivity induced by an external electric field in superconducting semimetals, metals and semiconductors is presented. It is shown that the inhomogeneous surface superconducting state deeply penetrates into the bulk of the sample. The dependence of the critical surface temperature and magnetic field on the external electric field is calculated.

Effect of the type-I to type-II Weyl semimetal topological transition on superconductivity

The influence of recently discovered topological transition between type I and type II Weyl semi-metals on superconductivity is considered. A set of Gorkov equations for weak superconductivity in Weyl semi-metal under topological phase transition is derived and solved. The critical temperature and superconducting gap both have spike in the point the transition point as function of the tilt parameter of the Dirac cone determined in turn by the material parameters like pressure. The spectrum of superconducting excitations is different in two phases: the sharp cone pinnacle is characteristic for a type I, while two parallel almost flat bands, are formed in type II. Spectral density is calculated on both sides of transition demonstrate different weight of the bands. The superconductivity thus can be used as a clear indicator for the topological transformation. Results are discussed in the light of recent experiments.