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

TL;DR

This study investigates how high pressure resistivity measurement and high pressure annealing differently affect the superconducting properties of Bi2(O,F)S2, revealing distinct impacts on Tc and lattice structure.

Contribution

It demonstrates that high pressure annealing can preserve or induce superconductivity in BiS2-based compounds, unlike pressure measurement which suppresses Tc.

Findings

Tc decreases linearly under pressure during resistivity measurement

High pressure annealing maintains Tc despite lattice changes

Superconductivity appears in fluorine-free Bi2OS2 after annealing

Abstract

Pressure effects on a recently discovered BiS2-based superconductor Bi2(O,F)S2 (Tc = 5.1 K) were examined via 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 by the cubic-anvil-type apparatus. In high pressure resistivity measurement, Tc linearly decreased at the 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{\deg}C of optimally doped sample despite significant change of lattice parameters. In addition, superconductivity was observed in fluorine-free Bi2OS2 after high pressure annealing. These results suggest that high pressure annealing would cause a unique effect on physical properties of layered compounds.