title: Origin of the spin density wave instability in AFe2As2 (A=Ba,Sr) as revealed by optical spectroscopy.
abstract: We performed optical spectroscopy measurement on single crystals of BaFe2As2 and SrFe2As2, the parent compounds of FeAs-based superconductors. Both are found to be quite metallic with fairly large plasma frequencies at high temperature. Upon entering the spin-density-wave state, the formation of partial energy gaps was clearly observed with the surprising presence of two different energy scales. A large part of the Drude component was removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate was even more dramatically reduced. We elaborate that the spin-density-wave instability is more likely to be driven by the Fermi surface nesting of itinerant electrons than a local-exchange mechanism.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: W Z
authors.initials: WZ
authors.lastname: Hu
authors.forename: J
authors.initials: J
authors.lastname: Dong
authors.forename: G
authors.initials: G
authors.lastname: Li
authors.forename: Z
authors.initials: Z
authors.lastname: Li
authors.forename: P
authors.initials: P
authors.lastname: Zheng
authors.forename: G F
authors.initials: GF
authors.lastname: Chen
authors.forename: J L
authors.initials: JL
authors.lastname: Luo
authors.forename: N L
authors.initials: NL
authors.lastname: Wang