Symmetry conditions for the superconducting diode effect in chiral superconductors

TL;DR

This paper investigates the symmetry conditions necessary for the superconducting diode effect in chiral superconductors, demonstrating how spontaneous edge currents and broken time-reversal symmetry lead to non-reciprocal critical currents.

Contribution

It derives the symmetry criteria for the superconducting diode effect and applies them to specific examples, linking the effect to broken time-reversal symmetry in chiral superconductors.

Findings

Spontaneous edge currents contribute to critical current splitting.

Broken time-reversal symmetry is essential for the diode effect.

The observed effect in Sr₂RuO₄ indicates broken TRS in its superconducting phase.

Abstract

We analyze the presence of non-reciprocal critical currents, the so-called superconducting diode effect, in chiral superconductors within a generalized Ginzburg-Landau framework. After deriving its key symmetry conditions we illustrate the basic mechanism for two examples, the critical current in a thin film and a Josephson junction. The appearance of spontaneous edge currents and the energy bias for the formation of Josephson vortices play an essential part in establishing a splitting of the critical currents running in opposite directions. Eventually, this allows us to interpret a superconducting diode effect observed in the 3-Kelvin phase of Sr$_2$RuO$_4$ as evidence for spontaneously broken time-reversal symmetry in the superconducting phase.