Conférence de physique du 14 juillet 2025

To Be, or not to be: Time-reversal symmetry breaking superconductivity in Sr₂RuO₄

Hans-Hnning Klauss, IFMP, Faculty of Physics, TU Dresden, Germany

After three decades of research, the symmetry of the superconducting state in Sr₂RuO₄ is still under strong debate [1]. The long time favoured spin-triplet p_x + i p_y state is ruled out by NMR experiments [2]. However, in general time-reversal-symmetry breaking (TRSB) superconductivity indicates complex two-component order parameters. Probing Sr₂RuO₄ under uniaxial pressure offers the possibility to lift the degeneracy between such components [3]. We reported results of muon spin relaxation (μSR) measurements on Sr₂RuO₄ placed under uniaxial stress. We observed a large pressure-induced splitting between the onset temperatures of superconductivity (Tc) and TRSB (T_TRSB). Moreover, at high stress beyond the van Hove singularity, a new spin density wave ordered phase is observed. To distinguish between a symmetry protected chiral state (d+id) and non-chiral accidentally degenerated order parameters (d+ig, f+ig) we reported SR studies under symmetry conserving hydrostatic pressure. In these experiment no splitting between Tc and T_TRSB is observed [4]. 

In this talk we want to discuss if and how these µSR specific observations can be consistent with proposals of single component sc order parameters deduced from recent thermodynamic observations.