# Time-Reversal Invariant Superconductivity of Sr$_{2}$RuO$_{4}$ Revealed by Josephson Effects

## TL;DR

This study uses Josephson junction experiments to demonstrate that Sr$_{2}$RuO$_{4}$ exhibits time-reversal invariant superconductivity, likely helical p-wave, challenging previous assumptions of chiral p-wave pairing.

## Contribution

It introduces a novel Josephson-based test for time-reversal symmetry, providing evidence for a helical p-wave state in Sr$_{2}$RuO$_{4}$, suggesting topological crystalline superconductivity.

## Key findings

- Sr$_{2}$RuO$_{4}$ shows time-reversal invariant superconductivity.
- The superconducting state is likely helical p-wave.
- Potential for hosting Majorana modes protected by mirror symmetry.

## Abstract

Sr$_{2}$RuO$_{4}$ is one of the most promising candidates of a topological superconductor with broken time-reversal symmetry, because a number of experiments have revealed evidences for a spin-triplet chiral $p$-wave superconductivity. In order to clarify the time-reversal symmetry of Sr$_{2}$RuO$_{4}$, we introduce a novel test that examines the invariance of the Josephson critical current under the inversion of both the current and magnetic fields, in contrast to the detection of a spontaneous magnetic field employed in past experiments. Analyses of the transport properties of the planar and corner Josephson junctions formed between Sr$_{2}$RuO$_{4}$ and Nb reveal the time-reversal invariant superconductivity, most probably helical $p$-wave, of Sr$_{2}$RuO$_{4}$. This state corresponds to a yet-to-be confirmed $topological crystalline superconductivity$ that can host two Majorana edge modes at the surface protected by crystalline mirror symmetry.