Speaker
Description
After two decades of research, the symmetry of the superconducting state in Sr$_2$RuO$_4$ is still under strong debate. The long time favoured spin-triplet px + i py state is ruled out by recent NMR experiments (1). However, in general time-reversal-symmetry breaking (TRSB) superconductivity indicates complex two-component order parameters. Probing Sr$_2$RuO$_4$ under uniaxial pressure offers the possibility to lift the degeneracy between such components (2). One key prediction for Sr$_2$RuO$_4$, a splitting of the superconducting and TRSB transitions under uniaxial pressure has not been observed so far.
Here, we report results of muon spin relaxation (μSR) measurements on Sr$_2$RuO$_4$ placed under uniaxial stress (3). We observed a large pressure-induced splitting between the onset temperatures of superconductivity (T$_c$) and TRSB (T$_{\mathrm{TRSB}}$). 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 also report $\mu$SR studies under symmetry conserving hydrostatic pressure. In these experiment no splitting between T$_c$ and T$_{\mathrm{TRSB}}$ is observed (4).
In this talk we discuss the implications on the superconducting order parameter in Sr$_2$RuO$_4$.
*This work was supported by DFG (GR 4667, GRK 1621, and SFB 1143).
(1) A. Pustogow, et al., Nature 574, 72 (2019)
(2) C. Hicks, et al., Science 344, 283 (2014), M. E. Barber, et al., Phys. Rev. Lett. 120, 076602 (2018).
(3) V. Grinenko, S. Ghosh, et al., Nat. Phys. (2021)
(4) V. Grinenko, et al., Nat. Comm. (2021)
