  We report the superconductivity at above 30 K in a new FeSe-layer compound
K0.8Fe2Se2 (nominal composition) achieved by metal K intercalating in between
FeSe layers. It is isostructural to BaFe2As2 and possesses the highest Tc for
FeSe-layer materials so far under ambient pressure. Hall effect indicates the
carriers are dominated by electron in this superconductor. We confirm that the
observed superconductivity at above 30 K is due to this new FeSe-based 122
phase. Our results demonstrate that FeSe-layer materials are really remarkable
superconductors via structure and carrier modulation.
