Spontaneous superconducting diode effect in non-magnetic Nb/Ru/Sr$_2$RuO$_4$ topological junctions

TL;DR

This paper reports the discovery of a superconducting diode effect in non-magnetic Nb/Ru/Sr2RuO4 junctions, demonstrating intrinsic time-reversal symmetry breaking and topological properties without external magnetic fields.

Contribution

It introduces a novel non-magnetic topological Josephson junction exhibiting spontaneous superconducting diode effect, advancing understanding of symmetry breaking in superconductors.

Findings

Superconducting diode effect observed without external magnetic field.

SDE depends on cooling history, indicating intrinsic symmetry breaking.

Magnetic fields influence SDE by altering non-reciprocity sign.

Abstract

Non-reciprocal electronic transport in a material occurs if both time reversal and inversion symmetries are broken. The superconducting diode effect (SDE) is an exotic manifestation of this type of behavior where the critical current for positive and negative currents are mismatched, as recently observed in some non-centrosymmetric superconductors with a magnetic field. Here, we demonstrate a SDE in non-magnetic Nb/Ru/Sr$_2$RuO$_4$ Josephson junctions without applying an external magnetic field. The cooling history dependence of the SDE suggests that time-reversal symmetry is intrinsically broken by the superconducting phase of Sr$_2$RuO$_4$. Applied magnetic fields modify the SDE dynamically by randomly changing the sign of the non-reciprocity. We propose a model for such a topological junction with a conventional superconductor surrounded by a chiral superconductor with broken time reversal symmetry.