Pressure Study of BiS2-Based Superconductors Bi4O4S3 and La(O,F)BiS2

We report the electrical resistivity measurements under pressure for the recently discovered BiS 2 -based layered superconductors Bi 4 O 4 S 3 and La(O,F)BiS 2 . In Bi 4 O 4 S 3 , the transition temperature T c decreases monotonically without a distinct change in the metallic behavior in the normal state. In La(O,F)BiS 2 , on the other hand, T c initially increases with increasing pressure and then decreases above ∼1 GPa. The semiconducting behavior in the normal state is suppressed markedly and monotonically, whereas the evolution of T c is nonlinear. The strong suppression of the semiconducting behavior without doping in La(O,F)BiS 2 suggests that the Fermi surface is located in the vicinity of some instability. In the present study, we elucidate that the superconductivity in the BiS 2 layer favors the Fermi surface at the boundary between the semiconducting and metallic behaviors.