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Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity.


ABSTRACT: Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe(0.6)Se(0.4)(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV (~8 K) above EF at the Γ-point, which shows a sharp superconducting coherence peak with gap formation below Tc. The estimated superconducting gap Δ and Fermi energy [Symbol: see text]F indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.

SUBMITTER: Okazaki K 

PROVIDER: S-EPMC3937798 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity.

Okazaki K K   Ito Y Y   Ota Y Y   Kotani Y Y   Shimojima T T   Kiss T T   Watanabe S S   Chen C-T CT   Niitaka S S   Hanaguri T T   Takagi H H   Chainani A A   Shin S S  

Scientific reports 20140228


Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe(0.6)Se(0.4)(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-r  ...[more]

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