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

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(∥)) and perpendicular (R(⊥)) to the DC current, I(DC), is measured with various magnetic fields. R(∥) and R(⊥) show contrasting dependence on I(DC). First, the critical current of R(∥) is smaller than that of R(⊥). Second, R(⊥) shows an unexpected reduction at current bias where R(∥) 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(∥), which leads to the higher critical current in R(⊥). Complicated conduction profile may also allow the anomalous reduction in the R(⊥) before finally shifting to the normal state.