Emergence of Fulde-Ferrell-Larkin-Ovchinnikov phase in FeSe in the BCS-BEC crossover

ORAL

Abstract

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, predicted more than a half-century ago, is a highly exotic state of fermionic condensate, in which oscillations of the order parameter emerge in real space. Yet, quest of the FFLO phase has been a challenge for a broad range of scientists, including solid-state, ultracold atomic and high-energy physics. Here, via thermal transport measurements in intense magnetic fields up to 33 T, we present compelling evidence for a distinct high-field superconducting phase in an iron-chalcogenide superconductor FeSe for the field H || ab-plane. A discontinuous downward jump in the quasiparticle thermal transport indicates the presence of a first-order transition line within the superconducting phase. We attribute the high-field phase to the FFLO phase, where planar nodes are formed. We discuss the importance of the extremely small Fermi energies, strong spin-orbit coupling and multiband nature for the FFLO phase in FeSe.

*This work is supported by Grants-in-Aid for Scientific Research (KAKENHI) (Nos. 15H03688, 15KK0160, 18H01177, 18H05227, 19H00649) and on Innovative Areas "Topological Material Science" (No. 15H05852) "Quantum Liquid Crystals" (No. 19H05824) from JSPS. This work is also supported by HFML-RU and HLD-HZDR, members of the EMFL.

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Presenters

  • Shigeru Kasahara

    • Department of Physics, Kyoto University
    • Dept. Phys., Kyoto Univ.
    • Kyoto Univ
    • Physics, Kyoto University
    • Kyoto University

Authors

  • Shigeru Kasahara

    • Department of Physics, Kyoto University
    • Dept. Phys., Kyoto Univ.
    • Kyoto Univ
    • Physics, Kyoto University
    • Kyoto University

  • Yuki Sato

    • Department of Physics, Kyoto University
    • Dept. Phys., Kyoto Univ.
    • Kyoto Univ
    • Physics, Kyoto University

  • Salvatore Licciardello

    • High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University

  • Matija Čulo

    • High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University

  • Stevan Arsenijevic

    • Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf
    • Helmholtz-Zentrum Dresden-Rossendorf

  • Thom Ottenbros

    • High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University

  • Takahito Tominaga

    • Kyoto Univ

  • Jakob Böker

    • Ruhr-Universität Bochum
    • Ruhr-Universitat Bochum

  • Ilya Eremin

    • Institut für Theoretische Physik III, Ruhr-Universität Bochum
    • Ruhr-Universität Bochum
    • Ruhr-Universitat Bochum

  • Joachim Wosnitza

    • HLD (HZDR) / TU Dresden
    • Dresden High Magnetic Field Laboratory, Helmholtz Zentrum Dresden Rossendorf
    • Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf
    • Helmholtz-Zentrum Dresden-Rossendorf

  • Takasada Shibauchi

    • Advanced Materials Science, University of Tokyo
    • Univ of Tokyo-Kashiwanoha
    • Department of Advanced Materials Science, University of Tokyo
    • Univ of Tokyo
    • Dept. Adv. Mat. Sci., Univ. Tokyo
    • Univ. of Tokyo
    • Department of Advanced Materials Science, The University of Tokyo
    • Department of Advanced Material Science, University of Tokyo

  • Nigel Hussey

    • High Field Magnet Laboratory and Radboud Univ., Nijmegen, The Netherlands
    • HFML Nijmegen - Radboud University
    • High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University

  • Yuji Matsuda

    • Department of Physics, Kyoto University
    • Department of Physics, Kyoto Univ
    • Dept. Phys., Kyoto Univ.
    • Kyoto Univ
    • Physics, Kyoto University
    • Kyoto University