Superconducting Diode Effect in Two-dimensional Topological Insulator Edges and Josephson Junctions

The superconducting diode effect – the dependence of critical current on its direction – can arise from the simultaneous breaking of inversion and time-reversal symmetry in a superconductor and has gained interest for its potential applications in superconducting electronics. In this letter, we study the effect in a two-dimensional topological insulator (2D TI) in both a uniform geometry as well as in a long Josephson junction. We show that in the presence of Zeeman fields, a circulating edge current enables a large non-reciprocity of the critical current. We find a maximum diode efficiency 1 for the uniform 2D TI and $(\sqrt{2}-1{)}^2\approx 0.17$ for the long Josephson junction.