Time-reversal invariant superconductivity of Sr2RuO4 revealed by Josephson effects

Sr2RuO4 is one of the most promising candidates of a topological superconductor with broken time-reversal symmetry because a number of experiments have revealed evidence for a spin-triplet chiral p-wave superconductivity. To clarify the time-reversal symmetry of Sr2RuO4, we introduce a 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 Sr2RuO4 and Nb reveal the time-reversal invariant superconductivity, most probably helical p-wave symmetry, of Sr2RuO4. 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.