Extrinsic origin of nonreciprocal resistance in a non-chiral organic superconductor

Abstract

We investigate nonreciprocal conductivity in the superconducting state of the molecular conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl. Although the material is neither chiral nor polar, we have observed nonreciprocal resistance proportional to the applied current and in-plane magnetic field, which is comparable with that of gate-induced superconducting MoS2. However, we find that this nonreciprocal resistance exhibits significant sample dependence, with even its sign varying. Furthermore, within the same sample, its magnitude and sign varied depending on the measurement location, suggesting the existence of nonreciprocal resistance governed by a mechanism distinct from the Rashba effect in polar superconductors. The increase in nonreciprocal resistance due to current terminals with high contact resistance suggests the Nernst effect, arising from slight temperature gradients along the out-of-plane direction, as its origin. Utilizing this, we successfully increased the nonreciprocal coefficient by up to approximately twofold by processing the sample into a nonuniform shape.