Universal Josephson and normal-superconductor diodes*

In this work, we explore how nonreciprocal superconductivity can be probed through both nonreciprocity of a critical current through Josephson junctions as well as nonreciprocity of transport through N-S junctions. We propose a universal mechanism for the Josephson diode effect in short Josephson junctions. This mechanism is due to finite Cooper pair momentum and is a manifestation of simultaneous breaking of inversion and time-reversal symmetries. The diode efficiency is up to 40%, which corresponds to an asymmetry between the critical currents in opposite directions Ic+/Ic− ≈ 230%. We show that this arises from both the Doppler shift of the Andreev bound state energies and the phase-independent asymmetric current from the continuum. We propose a simple scheme for achieving finite-momentum pairing, which does not rely on spin-orbit coupling and thus greatly expands existing platforms for the observation of supercurrent diode effects. 

We also show that nonreciprocal superconductivity reveals itself in asymmetric current-voltage characteristic of a transparent planar N-S junction. This leads us to a proposal of normal metal-superconductor (N-S) diode, which can exhibit twofold higher resistance in one direction than the other. N-S diode setup can be used as a smoking-gun tool for studying no reciprocal superconductivity.