Pressure-induced antiferromagnetic transition and phase diagram in FeSe

TL;DR

This study investigates how high pressure affects the structural, magnetic, and superconducting phases of FeSe, revealing a pressure-induced antiferromagnetic transition and complex phase diagram with coexisting phases.

Contribution

It provides the first detailed measurements of resistance and magnetic susceptibility under high pressure, mapping the phase diagram and identifying the antiferromagnetic transition in FeSe.

Findings

Structural phase transition is suppressed above 18 kbar.

Superconducting Tc shows a nonmonotonic pressure dependence.

Antiferromagnetic transition appears around 11.6 kbar and coexists with superconductivity.

Abstract

We report measurements of resistance and ac magnetic susceptibility on FeSe single crystals under high pressure up to 27.2 kbar. The structural phase transition is quickly suppressed with pressure, and the associated anomaly is not seen above $\sim$18 kbar. The superconducting transition temperature evolves nonmonotonically with pressure, showing a minimum at $\sim12$ kbar. We find another anomaly at 21.2 K at 11.6 kbar. This anomaly most likely corresponds to the antiferromagnetic phase transition found in $\mu$SR measurements [M. Bendele \textit{et al.}, Phys. Rev. Lett. \textbf{104}, 087003 (2010)]. The antiferromagnetic and superconducting transition temperatures both increase with pressure up to $\sim25$ kbar and then level off. The width of the superconducting transition anomalously broadens in the pressure range where the antiferromagnetism coexists.