Superconducting diode effect from singlet-triplet mixing in disordered helical superconductors

The superconducting diode effect (SDE) -- the nonreciprocity of the critical current in a bulk superconductor -- has received a lot of attention recently due to promising applications in superconducting electronics. The effects of disorder on SDE, however, have rarely been considered, despite these effects having possible qualitative consequences, as we show in this work. In particular, we study the SDE in a disordered Rashba superconductor in an in-plane magnetic field, using a self-consistent Born approximation to derive the corresponding Ginzburg-Landau theory. We find two surprising effects. First, in the limit of strong Rashba SOC, we find that disorder is the driving mechanism of the SDE, which vanishes in the absence of disorder. In this case, we show that the SDE occurs due to the mixing of singlet and triplet superconducting orders induced by the disorder. Second, in the limit of weak Rashba spin-orbit coupling (SOC), we find that disorder can reverse the direction of the diode effect, signified by the sign change of the superconducting diode efficiency coefficient \(\eta\).