High-pressure studies on Tc and crystal structure of iron chalcogenide superconductors

摘要

The superconducting transition temperature, T_c, in iron-based solids can be enhanced by applied pressure: T_c increases from 8 to 37?K for the 11-type FeSe when the pressure is raised from 0 to 4?GPa. High-pressure studies can elucidate the mechanism of superconductivity in such novel materials. In this paper, we present a high-pressure study of Fe(Se_1?xTe_x) and Fe(Se_1?xS_x). In the case of Fe(Se_1?xTe_x), the maximum T_c under high pressure did not exceed the T_c of FeSe, which can be attributed to the structural transition to the monoclinic phase. For Fe(Se_1?xS_x) (0 x T_c exhibited a significant increase with pressure; however, the maximum T_c under high pressure did not exceed the T_c of FeSe. This may be due to the disorder induced by substituting S for Se, which is similar to the pressure effect on T_c for the 1111-type superconductor Ca(Fe_1?xCo_x)AsF. The T_c of Fe(Se_1?xS_x) showed a complex behavior below 1?GPa, first decreasing and then increasing with increasing pressure. From high-pressure x-ray diffraction measurements, the T_c (P) curve was correlated with the local structural parameter.