Suchergebnisse

The interplay of orbital and spin degrees of freedom is the fundamental characteristic in numerous condensed matter phenomena, including high-temperature superconductivity, quantum spin liquids, and topological semimetals. In iron-based superconductors (FeSCs), this causes superconductivity to emerge in the vicinity of two other instabilities: nematic and magnetic. Unveiling the mutual relationship among nematic order, spin fluctuations, and superconductivity has been a major challenge for research in FeSCs, but it is still controversial. Here, by carrying out 77Se nuclear magnetic resonance (NMR) measurements on FeSe single crystals, doped by cobalt and sulfur that serve as control parameters, we demonstrate that the superconducting transition temperature Tc increases in proportion to the strength of spin fluctuations, while it is independent of the nematic transition temperature Tnem. Our observation therefore directly implies that superconductivity in FeSe is essentially driven by spin fluctuations in the intermediate coupling regime, while nematic fluctuations have a marginal impact on Tc. © 2020, The Author(s). ; Semiconductor Research Corporation, SRC: 2018R1A5A6075964 ; Korea Basic Science Institute, KBSI: IBS-R014-D1 ; Kazan Federal University ; 2016K1A4A4A01922028 ; Government Council on Grants, Russian Federation ; Deutsche Forschungsgemeinschaft, DFG: BA 4927/ 2-1 ; National Research Foundation of Korea, NRF: EF86/7-1, BU887/25-1, 19-43-04129, NRF-2019R1F1A1057463 ; We acknowledge A. Chubukov for useful discussions. S.H.B. has been supported by the Deutsche Forschungsgemeinschaft (Germany) via DFG Research Grants BA 4927/ 2-1 and by the National Research Foundation of Korea (NRF-2019R1F1A1057463). D.V. E., B.B., I.M., and S.A. were supported by RSF-DFG project (no. 19-43-04129, BU887/25-1, EF86/7-1). D.V.E. and I.M. were also supported by VW foundation in the frame of the VW Trilateral Initiative. S.A. acknowledges financial support from Deutsche Forschungsgemeinschaft (DFG) via Grant No. DFG AS 523/4-1. The work at POSTECH was supported by Institute for Basic Science (no. IBS-R014-D1) and also by the National Research Foundation (NRF) of Korea through the SRC (no. 2018R1A5A6075964) and the Max Planck-POSTECH Center for Complex Phase Materials in Korea (MPK) (no. 2016K1A4A4A01922028). The work of DACh was supported by the program 211 of the Russian Federation Government, agreement No. 02.A03.21.0006, by the Russian Government Program of Competitive Growth of Kazan Federal University.