Magneto-Optical Observation of Anisotropic Critical Current Density in Nb Films with Artificial Asymmetric Pinning Potential

Abstract

We investigated the anisotropic motion of vortices in superconducting Nb films by theoretical analysis and magneto-optical (MO) imaging. To realize the anisotropic motion of vortices, we fabricated an array of step-like grooves with a periodicity of 5.0 µm and a length of 1.0 mm on 0.5-µm-thick Nb films. The asymmetric pinning potential of the vortices was generated by the array of step-like grooves. Theoretical analysis of the pinning potential around the steps revealed anisotropies in the elementary pinning force and critical current density. The MO images revealed an asymmetric flux distribution, thereby indicating an anisotropic critical current density, and the ratio of the maximum critical current density to the minimum critical current density was found to be 1.3.