Superconductivity of highly spin-polarized electrons in FeSe probed by Se77 NMR

S. Molatta, D. Opherden, J. Wosnitza, L. Opherden, Z. T. Zhang, T. Wolf, H. v. Löhneysen, R. Sarkar, P. K. Biswas, H.-J. Grafe, and H. Kühne
Phys. Rev. B 104, 014504 – Published 12 July 2021
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Abstract

A number of recent experiments indicate that the iron-chalcogenide FeSe provides the long-sought possibility to study bulk superconductivity in the cross-over regime between the weakly coupled Bardeen-Cooper-Schrieffer (BCS) pairing and the strongly coupled Bose-Einstein condensation (BEC). We report on Se77 nuclear magnetic resonance experiments of FeSe, focused on the superconducting phase for strong magnetic fields applied along the c axis, where a distinct state with large spin polarization was reported. We determine this high-field state as bulk superconducting with high spatial homogeneity of the low-energy spin fluctuations. Further, we find that the static spin susceptibility becomes unusually small at temperatures approaching the superconducting state, despite the presence of pronounced spin fluctuations. Taken together, our results clearly indicate that FeSe indeed features an unusual field-induced superconducting state of a highly spin-polarized Fermi liquid in the BCS-BEC crossover regime.

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  • Received 16 October 2020
  • Revised 25 June 2021
  • Accepted 29 June 2021

DOI:https://doi.org/10.1103/PhysRevB.104.014504

©2021 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Molatta1,2, D. Opherden1,2, J. Wosnitza1,2, L. Opherden1,2, Z. T. Zhang1,3, T. Wolf4, H. v. Löhneysen4,5, R. Sarkar2, P. K. Biswas6, H.-J. Grafe7, and H. Kühne1,*

  • 1Hochfeld-Magnetlabor Dresden (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
  • 2Institut für Festkörper- und Materialphysik, TU Dresden, 01062 Dresden Germany
  • 3Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China
  • 4Institut für Quantenmaterialien und -technologien, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany
  • 5Physikalisches Institut, Karlsruher Institut für Technologie, 76049 Karlsruhe, Germany
  • 6ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon, OX11 0QX, United Kingdom
  • 7IFW Dresden, Institute for Solid State Research, 01171 Dresden, Germany

  • *Corresponding author: h.kuehne@hzdr.de

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Issue

Vol. 104, Iss. 1 — 1 July 2021

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