费米能级上方电子能带中的超导性：通向BCS-BEC超导性的可能途径。
Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity.
作者信息
Okazaki K, Ito Y, Ota Y, Kotani Y, Shimojima T, Kiss T, Watanabe S, Chen C-T, Niitaka S, Hanaguri T, Takagi H, Chainani A, Shin S
机构信息
1] Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan [2].
Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
出版信息
Sci Rep. 2014 Feb 28;4:4109. doi: 10.1038/srep04109.
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.
传统超导遵循电子在动量空间配对的巴丁-库珀-施里弗（BCS）理论，而超流性是原子在实空间配对的玻色-爱因斯坦凝聚（BEC）。固体金属和超冷气体的这些性质分别通过BCS-BEC交叉联系起来。在这里，我们使用超高分辨率激光角分辨光电子能谱，在费米能级（EF）上下的可及范围内研究了FeTe(0.6)Se(0.4)（Tc = 14.5 K ~ 1.2 meV）中的能带色散。我们发现在Γ点处有一个位于EF上方仅0.7 meV（~8 K）的电子能带，它在Tc以下显示出具有能隙形成的尖锐超导相干峰。估计的超导能隙Δ和费米能量[符号：见正文]F表明铁基超导体中的复合超导性，由电子能带中的强耦合BEC和空穴能带中的弱耦合BCS类超导性组成。该研究确定了通往BCS-BEC超导性的可能途径。
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