Department of Physics, Shanghai University, Shanghai 200444, China.
Phys Rev Lett. 2012 Nov 2;109(18):187007. doi: 10.1103/PhysRevLett.109.187007.
Based on a phenomenological model and the Kubo formula, we investigate the superfluid density ρ(s)(T) and then the penetration depth λ(T) of the iron-based superconductors in the coexistence region of the spin-density wave and superconductivity, and also in the overdoped region. Our calculations show a dramatic increase of λ(0) with the decrease of the doping concentration x below x = 0.1. This result is consistent with the experimental observations. At low temperatures, ρ(s)(T) shows an exponential-law behavior, while at higher temperatures, the linear-in-T behavior is dominant before it trends to vanish. It is in qualitative agreement with the direct measurement of superfluid density in films of Fe-pnictide superconductor at x = 0.08. The evolution of Δλ(T) can be roughly fitted by a power-law function with the exponent depending on the doping concentration. We show that the Uemura relation holds for the iron-based superconductors only at very low doping levels.
基于唯象模型和 Kubo 公式，我们研究了铁基超导体在自旋密度波和超导共存区域以及过掺杂区域的超导态密度 ρ(s)(T)和穿透深度 λ(T)。我们的计算表明，在掺杂浓度 x 低于 0.1 时，λ(0)随着掺杂浓度的降低而急剧增加。这一结果与实验观察一致。在低温下，ρ(s)(T)表现出指数律行为，而在较高温度下，在趋于消失之前，线性依赖于 T 的行为占主导地位。这与在 x = 0.08 的 Fe- p nictide 超导体薄膜中超导态密度的直接测量结果定性相符。Δλ(T)的演化可以用幂律函数大致拟合，指数取决于掺杂浓度。我们表明，Uemura 关系仅在非常低的掺杂水平下适用于铁基超导体。
