Asymmetries of the Critical Surface Current in Type-II Superconductors

Abstract

It is found that in two different and well-defined experimental situations the magnitude of the critical surface current changes when the direction of the transport current is reversed. This property is denoted as "partial rectification." In one case (single-surface rectifier), the asymmetry is measured when the external magnetic field ($H_{c1\mathrm{}}<H<\mathrm{}{H}_{c3\mathrm{}}$) is directed parallel to a single, unpaired surface and perpendicular to the transport current directions. Here only a tentative explanation is offered. In the second case (asymmetric-field rectifier), the asymmetry can be understood with the assumptions: (1) that the critical surface state model applies, i.e., each region of the surface carries its maximum or critical current, and (2) that the local critical surface current decreases as the absolute magnitude of the local perpendicular field component is increased from zero. The asymmetry in the critical surface current occurs in foils when the perpendicular component of the applied magnetic field is zero along the center line of the foil ($x=0\mathrm{}$), increases with distance from the center line, and has the symmetry that $H_{\perp a}\mathrm{}\left(x\right)=-H_{\perp a}\mathrm{}(-x)\mathrm{}$.