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Although the normal-state electronic structure of Sr 2 RuO 4 is known with exceptional
precision, even after two decades of research, the symmetry of its certainly unconventional
superconducting state is under strong debate. In general, time-reversal-symmetry breaking
(TRSB) superconductivity indicates complex two-component order parameters. Probing
Sr 2 RuO 4 under uniaxial stress offers the possibility to lift the degeneracy between such
components. One key prediction for Sr 2 RuO 4 , a splitting of the superconducting and TRSB
transitions under uniaxial stress has not been observed so far. I will show results of muon spin
relaxation (μSR) measurements on Sr 2 RuO 4 placed under uniaxial stress, wherein a large
stress-induced splitting between the onset temperatures of superconductivity and TRSB was
observed [1]. Moreover, at high stress beyond the Van Hove singularity, a new spin density
wave ordered phase was detected for the first time. To perform μSR measurements under
uniaxial stress, a custom piezoelectric based pressure cell was developed [2]. This cell is
going to be useful for a range of other materials [3,4], in which the Fermi surface or magnetic
interaction strengths can be tuned leading to strong modifications of the electronic state. |