Pressure-Induced Enhancement of Superconductivity and Structural Transition in BiS2-Layered LaO1-xFxBiS2

BiS2-based LaO1-xFxBiS2 (x = 0.5) becomes superconductive at T-c = 2.5 K. Electrical resistivity and magnetization measurements are performed under pressure to determine the pressure dependence of the superconducting transition temperature T-c up to 18 GPa. We observe that T-c abruptly increases from 2.5 to 10.7K at a pressure of 0.7 GPa. According to high-pressure X-ray diffraction measurements of LaO1-xFxBiS2 (x = 0 and 0.5), a structural phase transition from tetragonal to monoclinic also occurs at similar to 0.8 GPa. We consider that the pressure-induced enhancement of superconductivity for LaO1-xFxBiS2 is caused by the structural phase transition.