Critical current and negative magnetoresistance of superconducting film with edge barrier

Abstract

PACS. 74.60.Ec -Mixed state, critical fields, and surface sheath.Abstract. -The field-dependent critical current Ic(H) and current-voltage characteristics are found within a generalized critical-state model that accounts for both surface barrier and bulk pinning as major irreversibility mechanisms in type-II superconductors. Calculations are made for an exactly solvable case of a thin-film superconductor taking into account the GinzburgLandau nonlinearity of the order-parameter equation. The shape of the current-voltage characteristics of the film is determined for arbitrary magnetic field. The nonmonotonous field dependence of the differential film resistivity is discovered, which is characterized by a negative magnetoresistance in a low-field region and by the Bardeen-Stephen-like behaviour in a high-field region.Introduction. -The edge/surface barrier effect on transport properties of type-two superconductors is at present under extensive investigation. The essential barrier influence on superconductor resistivity, that arises due to thermoactivative barrier overcoming, was recently demonstrated in [1, 2] on Bi-based single crystals with high demagnetization factor. The importance of surface barrier (SB) for a wide range of materials (including low-T c superconductors [3]) in affecting the transport as well as the magnetic properties of superconductors is at present widely recognized. The interplay between the barrier and bulk pinning being responsible for the emergence of the nontrivial magnetic flux structures in an external magnetic field [4,5] or in a transport-current-carry state [6,7] to a great extent determines both magnetic and resistive characteristics of low-dimensional superconductors.Some progress in describing magnetization features of superconducting samples with a reduced dimensionality (thin-film or single-crystalline sample with high demagnetization) is due to a highly developed technique employed to solve the corresponding integral equations [4,6]. However, the essentially long-range intervortex repulsion complicates significantly the theoretical investigation of the transport properties of superconductors with a high demagnetization factor. Therefore it is highly desirable to formulate an exactly solvable model of the critical/resistive state in thin-film superconductors, which accounts for major irreversibility mechanisms (edge barrier and bulk pinning).In the present letter we provide first a self-consistent consideration of the combined influence of the edge barrier and bulk pinning on the field dependence of the critical current, the

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