Strange metal and exotic superconductivity in FeSe1-xTex

SPICE Workshop on Unconventional Superconductors and Magnets May 12th - 14th, 2026

Takasada Shibauchi

Fe-chalcogenide superconductors have intriguing properties [1] including the nonmagnetic nematic order and its quantum critical points (QCPs), and possible time-reversal symmetry beraking (TRSB) in the superconducting state. I will review recent progress in the studies of FeSe1-xTex superconductors, which have been discussed to host topological superconductivity. From the zero-field muon spin relazation measuremetns, we have evidence for TRSB superconductivity in the bulk [2]. This suggests that the topological superconductivity discussed in this system is a unique case with the coexsistence between TRSB superconductivity and topologically nontrivial electronic structure. By suppressing the superconductivity by high magnetic fields, we uncover the strange metallic ground state hidden below the superconducting dome of nonmagnetic FeSe1-xTex, which harbors a QCP of pure electronic nematicity. Unlike the conventional quantum criticality, this strange metallic state does not appear in a fan-shaped region above the singular QCP but spans a wide compositional range [3], where pairing interactions are strengthened by nonmagnetic nematic critical fluctuations [4].This stands in sharp contrast to the much cleaner system FeSe1-xSx, which displays a quantum critical fan above nematic QCP [5], indicating that disorder-induced spatial randomness of the nematic fluctuations likely enlarges the QCP of FeSe1-xTex into an extended region of criticality.

References

  1. See, for a review, T. Shibauchi, T. Hanaguri, and Y. Matsuda, J. Phys. Soc. Jpn. 89, 102002 (2020).
  2. Roppongi, Y. Cai, K. Ogawa, S. Liu, G. Q. Zhao, M. Oudah, T. Fujii , K. Imamura, S. Fang, K. Ishihara, K. Hashimoto, K. Matsuura, Y. Mizukami, M. Pula, C. Young, I. Markovic, D. A. Bonn, T. Watanabe, A. Yamashita, Y. Mizuguchi, G. M. Luke, K. M. Kojima, Y. J. Uemura, and T. Shibauchi, Nat. Commun. 16, 6573 (2025).
  3. K. Ishida, K. Mukasa, S. Imajo, A. Hardy, M. Qiu, M. Saito, A. Patel, K. Matsuura, Y. Sugimura, Y. Uezono, T. Otsuka, N. E. Hussey, T. Watanabe, K. Kindo, and T. Shibauchi, (preprint).
  4. Mukasa, K. Ishida, S. Imajo, M. W. Qiu, M. Saito, K. Matsuura, Y. Sugimura, S. Liu, Y. Uezono, T. Otsuka, M. Culo, S. Kasahara, Y. Matsuda, N. E. Hussey, T. Watanabe, K. Kindo, and T. Shibauchi, Phys. Rev. X 13, 0011032 (2023).
  5. Licciardello, J. Buhot, J. Lu, J. Ayres, S. Kasahara, Y. Matsuda, T. Shibauchi, and N. E. Hussey, Nature 567, 213-217 (2019).