A BCS-like gap in the superconductor SmFeAsO

 magnesium alloy chips Since the discovery of high-transition-temperature (high- T c ) superconductivity in layered copper oxides, extensive effort hasbeen devoted to exploring the origins of this phenomenon. A T c higher than 40 K (about the theoretical maximum predicted fromBardeen–Cooper–Schrieffer theory 1 ), however, has been obtained only in the copper oxidesuperconductors. The highest reported value for non-copper-oxidebulk superconductivity is T c = 39 K in MgB 2 (ref. 2 ). The layered rare-earth metal oxypnictides LnOFeAs (where Ln isLa–Nd, Sm and Gd) are now attracting attention following thediscovery of superconductivity at 26 K in the iron-based LaO 1- x F x FeAs (ref. 3 ). Here we report the discovery of bulk superconductivity in therelated compound SmFeAsO 1- x F x , which has a ZrCuSiAs-type structure. Resistivity andmagnetization measurements reveal a transition temperature as highas 43 K. This provides a new material base for studying the originof high-temperature superconductivity.