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Giant superconducting fluctuations in the compensated semimetal FeSe at the BCS-BEC crossover

Kasahara, S.; Yamashita, T.; Shi, A.; Kabayashi, R.; Shimoyama, Y.; Watashige, T.; Ishida, K.; Terashima, T.; Wolf, T.; Hardy, F.; Meingast, C.; Löhneysen, H.von; Levchenko, A.; Shibauchi, T.; Matsuda, Y.

Abstract (englisch): The physics of the crossover between weak-coupling Bardeen–Cooper–Schrieffer (BCS) and strong-coupling Bose–Einstein condensate (BEC) limits gives a unified framework of quantum-bound (superfluid) states of interacting fermions. This crossover has been studied in the ultracold atomic systems, but is extremely difficult to be realized for electrons in solids. Recently, the superconducting semimetal FeSe with a transition temperature Tc=8.5 K has been found to be deep inside the BCS–BEC crossover regime. Here we report experimental signatures of preformed Cooper pairing in FeSe, whose energy scale is comparable to the Fermi energies. In stark contrast to usual superconductors, large non-linear diamagnetism by far exceeding the standard Gaussian superconducting fluctuations is observed below T*∼20 K, providing thermodynamic evidence for prevailing phase fluctuations of superconductivity. Nuclear magnetic resonance and transport data give evidence of pseudogap formation at ∼T*. The multiband superconductivity along with electron–hole compensation in FeSe may highlight a novel aspect of the BCS–BEC crossover physics.

Zugehörige Institution(en) am KIT Institut für Festkörperphysik (IFP)
Publikationstyp Zeitschriftenaufsatz
Jahr 2016
Sprache Englisch
Identifikator DOI: 10.1038/ncomms12843
ISSN: 2041-1723
URN: urn:nbn:de:swb:90-602450
KITopen ID: 1000060245
HGF-Programm 43.21.01; LK 01
Erschienen in Nature Communications
Band 7
Seiten 12843
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