Anisotropic transport induced by DC electrical current bias near the critical current

Abstract

We investigated the transport characteristics of a square shape superconducting Ta thin film under DC electrical current bias along the diagonal direction. The resistance parallel (R-parallel to) and perpendicular (R-perpendicular to) to the DC current, I-DC, is measured with various magnetic fields. R-parallel to and R-perpendicular to show contrasting dependence on I-DC. First, the critical current of R-parallel to is smaller than that of R-perpendicular to. Second, R-perpendicular to shows an unexpected reduction at current bias where R-parallel to shows a rapid increase near the transition from a flux flow state to a normal state. The intriguing anisotropic transport characteristics can be understood by the inhomogeneous current density profile over the square sample. Diagonal DC current induces an anisotropic current density profile where the current density is high near the biasing electrode and low at the center of the sample. Accordingly, the electrical transport in the perpendicular direction could remain less affected even near the critical current of R-parallel to, which leads to the higher critical current in R-perpendicular to. Complicated conduction profile may also allow the anomalous reduction in the R-perpendicular to before finally shifting to the normal state.