77Se NMR study of pairing symmetry and spin dynamics in KyFe2-xSe2
arXiv:1101.1017 · doi:10.1103/PhysRevLett.106.197001
Abstract
We present a 77Se NMR study of the newly discovered iron selenide superconductor KyFe2-xSe2, in which Tc = 32 K. Below Tc, the Knight shift 77K drops sharply with temperature, providing strong evidence for singlet pairing. Above Tc, Korringa-type relaxation indicates Fermi-liquid behavior. Our experimental results set strict constraints on the nature of possible theories for the mechanism of high-Tc superconductivity in this iron selenide system.
Chemical composition of crystals determined. Accepted in Physical Review Letters