Pressure Effects on Superconducting Properties of the BiS2-Based Superconductor Bi2(O,F)S2

Pressure effects on the recently discovered BiS2-based superconductor Bi2(O,F)S2 (Tc = 5.1 K) were examined by two different methods: high-pressure resistivity measurement and high-pressure annealing. The effects of these two methods on the superconducting properties of Bi2(O,F)S2 were significantly different, although in both methods, hydrostatic pressure is applied to the sample using a cubic-anvil-type apparatus. In high-pressure resistivity measurement, Tc linearly decreased at a rate of −1.2 K GPa−1. In contrast, the Tc of 5.1 K is maintained after high-pressure annealing under 2 GPa and 470 °C of an optimally doped sample despite a significant change in lattice parameters. In addition, superconductivity was observed in fluorine-free Bi2OS2 after high-pressure annealing. These results suggest that high-pressure annealing has a unique effect on the physical properties of layered compounds.