Critical current non-reciprocity in quasi-one-dimensional systems*

The recent observations of the superconducting diode effect pose the challenge to fully understand the necessary ingredients for non-reciprocal phenomena in superconductors. In this theoretical work, we focus on the non-reciprocity of  the critical current in a quasi-one-dimensional superconductor and analyze the roles of symmetry and topology on the superconducting diode effect. We define the critical current as the value of the supercurrent at which the quasiparticle excitation gap closes (depairing). Once the critical current is exceeded,  the quasiparticles can exchange energy with the superconducting condensate, giving rise to dissipation. Our minimal model can be microscopically derived as a  low-energy limit of a Rashba spin-orbit coupled superconductor in a Zeeman  field. Within the proposed model, we explore the nature of the non-reciprocal effects of the critical current both analytically and numerically. Our results quantify how system parameters  such as spin-orbit coupling and chemical potential affect the strength of the superconducting diode effect. Our theory provides a complementary description to the Ginzburg-Landau theory of the effect.