title: Unconventional anisotropic s-wave superconducting gaps of the LiFeAs iron-pnictide superconductor.
abstract: We have performed high-resolution angle-resolved photoemission spectroscopy on Fe-based superconductor LiFeAs (T(c)=18 K). We reveal multiple nodeless superconducting (SC) gaps with 2Δ/k(B)T(c) ratios varying from 2.8 to 6.4, depending on the Fermi surface (FS). We also succeeded in directly observing a gap anisotropy along the FS with magnitude up to ~30%. The anisotropy is fourfold symmetric with an antiphase between the hole and electron FSs, suggesting complex anisotropic interactions for the SC pairing. The observed momentum dependence of the SC gap offers an excellent opportunity to investigate the underlying pairing mechanism.
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Umezawa
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: H
authors.initials: H
authors.lastname: Miao
authors.forename: K
authors.initials: K
authors.lastname: Nakayama
authors.forename: Z-H
authors.initials: ZH
authors.lastname: Liu
authors.forename: P
authors.initials: P
authors.lastname: Richard
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.forename: J B
authors.initials: JB
authors.lastname: He
authors.forename: D-M
authors.initials: DM
authors.lastname: Wang
authors.forename: G F
authors.initials: GF
authors.lastname: Chen
authors.forename: H
authors.initials: H
authors.lastname: Ding
authors.forename: T
authors.initials: T
authors.lastname: Takahashi
authors.forename: S-C
authors.initials: SC
authors.lastname: Wang