The FeSe1-xSx superconductors involving non-magnetic nematic phase and its quantum criticality provide a unique platform to investigate the relationship between nematicity and superconductivity . It has been shown that across the nematic quantum critical point, the superconducting properties change drastically [2,3], and the non-nematic tetragonal FeSe1-xSx (x>0.17) exhibits substantial low-energy states despite the high-quality of crystals. Here we have perform the muon spin rotation (μSR) measurements on FeSe1-xSx (x=0, 0.20, 0.22) and observed the spontaneous internal field below the superconducting transition temperature Tc, providing strong evidence for time-reversal breaking (TRSB) state in bulk FeSe1-xSx . We also find that the superfluid density in the tetragonal crystals is suppressed from the expected value, indicating the presence of non-superconducting carriers. These results in FeSe1-xSx are consistent with the recently proposed topological phase transition to a novel ultranodal pair state with Bogoliubov Fermi surface . See, for a review, T. Shibauchi, T. Hanaguri, and Y. Matsuda, J. Phys. Soc. Jpn. (in press); arXiv:2005.07315 (2020).
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 C. Setty, S. Bhattacharyya, Y. Cao, A. Kreisel, and P. J. Hirschfeld, Nat. Commun.11, 523 (2020).