Superconducting State of the Two-Dimensional Superconductor α-(ET)2NH4Hg(SCN)4 Under the Magnetic Field Parallel to the Conducting Plane

Abstract

The resistive transition to the superconducting (SC) state in α-(ET)2NH4Hg(SCN)4 was studied under magnetic fields applied parallel to the conducting plane. The SC state is divided into three regions: (1) temperature-dependent resistive region, (2) zero-resistive region, and (3) temperature-independent resistive region. We observed twofold symmetry in the resistance under an in-plane magnetic field near the midpoint of the SC transition, which indicates that the upper critical field μ0Hc2 has the same twofold symmetry. This in-plane anisotropy can be ascribed to the crystal structure.