title: 77Se NMR study of the pairing symmetry and the spin dynamics in K(y)Fe(2-x)Se2.
abstract: We present a 77Se NMR study of the newly discovered iron selenide superconductor K(y)Fe(2-x)Se2, in which T(c) = 32  K. Below T(c), the Knight shift 77K drops sharply with temperature, providing strong evidence for singlet pairing. Above T(c), Korringa-type relaxation indicates Fermi-liquid behavior. Our experimental results set strict constraints on the nature of possible theories for the mechanism of high-T(c) superconductivity in this iron selenide system.
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, China. wqyu_phy@ruc.edu.cn
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Yu
authors.forename: L
authors.initials: L
authors.lastname: Ma
authors.forename: J B
authors.initials: JB
authors.lastname: He
authors.forename: D M
authors.initials: DM
authors.lastname: Wang
authors.forename: T-L
authors.initials: TL
authors.lastname: Xia
authors.forename: G F
authors.initials: GF
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Bao