Intrinsic superconducting diode effect*

Nonreciprocal transport phenomena are attracting much attention as a new functionality of materials [1,2].  Recently, it has been observed in a Nb/V/Ta superlattice without an inversion center that the critical current for the phase transition between normal and superconducting states is different between the leftward and the rightward electric currents. Such a nonreciprocity of the critical current is called the superconducting diode effect (SDE) [3]. SDE might be applicable to dissipationless electric circuits and is an intriguing phenomenon manifesting the interplay between superconductivity and the inversion-symmetry breaking. It is an important issue to study how the SDE occurs to further promote the experimental/theoretical works.

In this study, we clarify that the critical current of noncentrosymmetric superconductors can become intrinsically nonriciprocal [4], by studying the nonreciprocity of the depairing critical current. We reveal the temperature scaling of the intrinsic SDE near the transition temperature as well as its significant enhancement at low temperatures. In particular, the low-temperature SDE is found to be closely related to the finite center-of-mass momentum Cooper pairs (called helical superconductivity). SDE could play an important role as a promising bulk probe of the helical superconductivity. We also discuss the relationship between the SDE and the nonreciprocity of the transition lines under supercurrent.