Dispersive x-ray absorption studies at the Fe K-edge on the iron chalcogenide superconductor FeSe under pressure

The local structure and the electronic properties of FeSe under hydrostatic pressure were studied by means of dispersive x-ray absorption measurements at the Fe K-edge. The pressure dependence of the x-ray absorption near edge structure features seems to follow the behavior of the superconducting transition temperature T-c. The local structure, that has an important impact on the superconducting properties, appears to fall into two regimes: the pressure dependence of the Fe-Fe bond distance shows a clear change in the compressibility at p similar to 5 GPa; in contrast, the Fe-Se bond distance decreases continuously with increasing pressure with a lower compressibility than the Fe-Fe bond. The results suggest that the pressure dependent changes in T-c of FeSe are closely related to the changes in local structure.