title: Superfluid density in the s±-wave state of clean iron-based superconductors.
abstract: 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.
authors.affiliation: Department of Physics, Shanghai University, Shanghai 200444, China.
authors.forename: Huaixiang
authors.initials: H
authors.lastname: Huang
authors.forename: Yi
authors.initials: Y
authors.lastname: Gao
authors.forename: Jian-Xin
authors.initials: JX
authors.lastname: Zhu
authors.forename: C S
authors.initials: CS
authors.lastname: Ting