title: Evidence for two energy gaps in superconducting Ba0.6K0.4Fe2As2 single crystals and the breakdown of the Uemura plot.
abstract: We report a detailed investigation on the lower critical field H{c1} of the superconducting Ba0.6K0.4Fe2As2 (122) single crystals. A pronounced kink is observed on the H{c1}(T) curve, which is attributed to the existence of two superconducting gaps. By fitting the data H{c1}(T) to the two-gap BCS model in the full temperature region, a small gap of Delta{a}(0)=2.0+/-0.3 meV and a large gap of Delta{b}(0)=8.9+/-0.4 meV are obtained. The in-plane penetration depth lambda{ab}(0) is estimated to be 105 nm corresponding to a rather large superfluid density, which points to the breakdown of the Uemura plot in 122 superconductors.
authors.affiliation: National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China. cong_ren@aphy.iphy.ac.cn
authors.forename: Cong
authors.initials: C
authors.lastname: Ren
authors.forename: Zhao-Sheng
authors.initials: ZS
authors.lastname: Wang
authors.forename: Hui-Qian
authors.initials: HQ
authors.lastname: Luo
authors.forename: Huan
authors.initials: H
authors.lastname: Yang
authors.forename: Lei
authors.initials: L
authors.lastname: Shan
authors.forename: Hai-Hu
authors.initials: HH
authors.lastname: Wen