Identifying Unconventional Pairing through Nonreciprocal Transport

The detection of unconventional superconductivity has posed a persistent challenge, especially when unconventional pairing is obscured by dominant conventional s-wave pairing. In this study, we carry out the investigation of a nonreciprocal transport phenomenon known as the anomalous shift at the interface of a 2D metal-superconductor junction. We find an explicit relationship between the accumulative anomalous shift (AAS) of particles at the Fermi surface and the pairing symmetry of the superconductor. This establishes a general framework that converts the challenge of measuring the unconventional pairing into the exploration the shift current induced by AAS. Furthermore, we validate our theoretical approach through examining typical examples such as mixed s − p paring and s − d paring. We also demonstrate the experimental feasibility of detecting unconventional pairing by measuring the nonreciprocal conductance in a multiple-terminal device. Our work opens up a new perspective for detecting pairing symmetry and advancing our understanding of the nature of Cooper pairs.