title: Gap opening and orbital modification of superconducting FeSe above the structural distortion.
abstract: We utilize steady-state and transient optical spectroscopies to examine the responses of nonthermal quasiparticles with respect to orbital modifications in normal-state iron-chalcogenide superconductors. The dynamics shows the emergence of gaplike quasiparticles (associated with a ~36 meV energy gap) with a coincident transfer of the optical spectral weight in the visible range, at temperatures above the structural distortion. Our observations suggest that opening of the high-temperature gap and the lattice symmetry breaking are possibly driven by short-range orbital and/or charge orders, implicating a close correlation between electronic nematicity and precursor order in iron-based superconductors.
authors.affiliation: Institute of Physics, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Y-C
authors.initials: YC
authors.lastname: Wen
authors.forename: K-J
authors.initials: KJ
authors.lastname: Wang
authors.forename: H-H
authors.initials: HH
authors.lastname: Chang
authors.forename: J-Y
authors.initials: JY
authors.lastname: Luo
authors.forename: C-C
authors.initials: CC
authors.lastname: Shen
authors.forename: H-L
authors.initials: HL
authors.lastname: Liu
authors.forename: C-K
authors.initials: CK
authors.lastname: Sun
authors.forename: M-J
authors.initials: MJ
authors.lastname: Wang
authors.forename: M-K
authors.initials: MK
authors.lastname: Wu