title: Measurement of the c-axis optical reflectance of AFe2As2 (A=Ba, Sr) single crystals: evidence of different mechanisms for the formation of two energy gaps.
abstract: We present the c-axis optical reflectance measurement on single crystals of BaFe2As2 and SrFe2As2, the parent compounds of FeAs based superconductors. Different from the ab-plane optical response where two distinct energy gaps were observed in the spin-density-wave (SDW) state, only the smaller energy gap could be seen clearly for E∥c axis. The very pronounced energy gap structure seen at a higher energy scale for E∥ab plane is almost invisible. We propose a novel picture for the band structure evolution across the SDW transition and suggest different driving mechanisms for the formation of the two energy gaps.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Z G
authors.initials: ZG
authors.lastname: Chen
authors.forename: T
authors.initials: T
authors.lastname: Dong
authors.forename: R H
authors.initials: RH
authors.lastname: Ruan
authors.forename: B F
authors.initials: BF
authors.lastname: Hu
authors.forename: B
authors.initials: B
authors.lastname: Cheng
authors.forename: W Z
authors.initials: WZ
authors.lastname: Hu
authors.forename: P
authors.initials: P
authors.lastname: Zheng
authors.forename: Z
authors.initials: Z
authors.lastname: Fang
authors.forename: X
authors.initials: X
authors.lastname: Dai
authors.forename: N L
authors.initials: NL
authors.lastname: Wang