Onset Temperatures for Superconducting Fluctuations in Te-annealed FeTe<sub>1−</sub><i><sub>x</sub></i>Se<i><sub>x</sub></i> Single Crystals: Evidence for the BCS–BEC Crossover

DOI DOI Web Site 21 References
  • Yu Uezono
    Graduate School of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan
  • Takumi Otsuka
    Graduate School of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan
  • Shotaro Hagisawa
    Graduate School of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan
  • Haruka Taniguchi
    Graduate School of Engineering, Iwate University, Morioka 020-8551, Japan
  • Michiaki Matsukawa
    Graduate School of Engineering, Iwate University, Morioka 020-8551, Japan
  • Takenori Fujii
    Cryogenic Research Center, University of Tokyo, Bunkyo, Tokyo 113-0032, Japan
  • Takao Watanabe
    Graduate School of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan

Description

Recently, the superconductors' community has witnessed an unsettled debate regarding whether iron-based superconductors, in particular FeSe and FeSe$_{1-x}$S$_x$, are in the Bardeen-Cooper-Shrieffer (BCS) - Bose-Einstein condensation (BEC) crossover regime. Nonetheless, one particular system, FeTe$_{1-x}$Se$_x$, has been less investigated in this regard owing to the screening of its intrinsic superconducting properties by the inevitable iron excess. Herein, the onset temperatures for superconducting fluctuations ($T_{scf}$) are investigated by measuring the magnetoresistance (MR) of Te-annealed, high-quality FeTe$_{1-x}$Se$_x$ ($x$ = 0.1, 0.2, 0.3, and 0.4) single crystals. The results reveal very high $T_{scf}$ values for these crystals. Particularly for $x$ = 0.4, $T_{scf}$ reaches approximately 40 K, which is 2.7 times larger than $T_c$. This indicates that the superconductivity of the FeTe$_{1-x}$Se$_x$ system is well within the BCS-BEC crossover regime.

6 pages, 3 figures, and 1 table. to be published in JPS Conference Proceedings

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