by uniaxial strain*

Although the normal-state electronic structure of Sr₂RuO₄ is known with exceptional precision, even after two decades of research, the symmetry of it’s certainly unconventional superconducting state is currently under strong debate, e.g. the long time favoured spin-triplet p_x + i p_y 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 Sr₂RuO₄ under uniaxial offers the possibility to lift the degeneracy between such components [2]. One key prediction for Sr₂RuO₄, a splitting of the superconducting and TRSB transitions under uniaxial stress has not been observed so far.
Here, we report results of muon spin relaxation (μSR) measurements on Sr₂RuO₄ placed under uniaxial stress. We observed a large stress-induced splitting between the onset temperatures of superconductivity and TRSB. Moreover, at high stress beyond the van Hove singularity [2], the TRSB phase is suppressed and a long-range ordered magnetic spin density wave phase is observed with an approx. 50 times stronger internal field.
We will discuss the uniaxial strain dependent electronic phase diagram and its implications for the symmetry of the superconducting order parameter in Sr₂RuO₄.




[1] A. Pustogow, et al., arXiv:1904.00047; K. Ishida et al., arXiv:1907.12236.
[2] C. Hicks, et al., Science 344, 283 (2014), M. E. Barber, et al., Phys. Rev. Lett. 120, 076602 (2018).