铁砷化物超导体LiFeAs中各向同性三维能隙的定向热输运测量
Isotropic three-dimensional gap in the iron-arsenide superconductor LiFeAs from directional heat transport measurements
摘要：
在温度低至50 mK和磁场高至H= 17 T（非常接近上临界磁场Hc ~ 2 ~ 18 T）的条件下，测量了砷化铁超导体LiFeAs（Tc ~ 18 K）的单晶热导率k。对于平行于和垂直于四极轴的两个热流方向，当T ->0时，都存在一个可忽略的剩余线性项k/T，表明超导态中不存在零能准粒子。在两个电流方向上，k随磁场的增加是相同的，并且它紧密地遵循对于各向同性超导能隙预期的依赖性。没有证据表明存在多带特征，因此在不同的费米面片上，带隙会有所不同。这些结果表明，超导能隙在LiFeAs中是各向同性的三维，没有节点或深极小的费米表面上的任何地方。与其他铁-磷属元素化物超导体的比较表明，无节点的各向同性间隙是最佳掺杂（最大Tc）的共同特征。
英文摘要：
The thermal conductivity k of the iron-arsenide superconductor LiFeAs (Tc ~ 18K) was measured in single crystals at temperatures down to T~50mK and in magnetic fields up to H=17T, very close to the upper critical field Hc2~18T. For both directions of the heat current, parallel and perpendicular to the tetragonal c-axis, a negligible residual linear term k/T is found as T ->0, revealing that there are no zero-energy quasiparticles in the superconducting state. The increase in k with magnetic field is the same for both current directions and it follows closely the dependence expected for an isotropic superconducting gap. There is no evidence of multi-band character, whereby the gap would be different on different Fermi-surface sheets. These findings show that the superconducting gap in LiFeAs is isotropic in 3D, without nodes or deep minima anywhere on the Fermi surface. Comparison with other iron-pnictide superconductors suggests that a nodeless isotropic gap is a common feature at optimal doping (maximal Tc).
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