Superconductivity and abnormal pressure effect in Sr0.5La0.5FBiSe2 superconductor

Through the solid state reaction method, we synthesized a new BiSe2-based superconductor SrLaFBiSe2 with superconducting transition temperature T K. A strong diamagnetic signal below T c in susceptibility is observed indicating the bulk nature of superconductivity. Different to most BiS2-based compounds where superconductivity develops from a semiconducting-like normal state, the present compound exhibits a metallic behavior down to T c . Under weak magnetic field or pressure, however, a remarkable crossover from metallic to insulating behaviors takes place around T min where the resistivity picks up a local minimum. With increasing pressure, T decreases monotonously and T min shifts to high temperatures, while the absolute value of the normal state resistivity at low temperatures first decreases and then increases with pressure up to 2.5 GPa. These results imply that the electronic structure of SrLaFBiSe2 may be different to those in the other BiS2-based systems.