Superconducting and normal phases of FeSe single crystals at high pressure

TL;DR

This study investigates the effects of high pressure on FeSe single crystals, revealing an increase in superconducting transition temperature up to 36 K and a structural phase transition from tetragonal to hexagonal at high pressures.

Contribution

It provides new insights into the pressure-induced superconducting and structural phase transitions in FeSe single crystals, combining magnetic, resistivity, and X-ray diffraction analyses.

Findings

TC increases up to 36 K under pressure

Structural transition from tetragonal to hexagonal occurs between 8.5 and 12 GPa

Superconductivity disappears above 12 GPa

Abstract

We report on the synthesis of superconducting single crystals of FeSe, and their characterization by X-ray diffraction, magnetization and resistivity. We have performed ac susceptibility measurements under high pressure in a hydrostatic liquid argon medium up to 14 GPa and we find that TC increases up to 33-36 K in all samples, but with slightly different pressure dependences on different samples. Above 12 GPa no traces of superconductivity are found in any sample. We have also performed a room temperature high pressure X-ray diffraction study up to 12 GPa on a powder sample, and we find that between 8.5 GPa and 12 GPa, the tetragonal PbO structure undergoes a structural transition to a hexagonal structure. This transition results in a volume decrease of about 16%, and is accompanied by the appearance of an intermediate, probably orthorhombic phase.