Anomalous Pressure Dependence of the Superconducting Transition Temperature in FeSe1-x Studied by DC Magnetic Measurements

TL;DR

This study investigates how the superconducting transition temperature in FeSe compounds varies with pressure, revealing a two-step increase, saturation at high pressures, and signs of electronic inhomogeneity.

Contribution

It provides new insights into the pressure dependence of $T_c$ in FeSe, highlighting anomalous behavior and electronic inhomogeneity effects not previously documented.

Findings

$T_c$ exhibits a two-step increase with pressure.

Superconducting volume fraction decreases as $T_c$ increases above 1.5 GPa.

$T_c$ saturates at around 25 K for pressures above 3 GPa.

Abstract

The pressure dependence of superconducting transition temperature $T_{\rm c}$ has been investigated through the DC magnetic measurements for FeSe$_{0.8}$ and FeSe$_{1.0}$. For both samples, with increasing pressure $P$, the $T_{\rm c}$$-$$P$ curve exhibits a two-step increase, showing a local maximum of $\sim$11 K at $P$$\sim$1.0 GPa and a rapid increase with an extremely large pressure coefficient for $P$$>$1.5 GPa. $T_{\rm c}$ saturates at $\sim$25 K (21 K) in FeSe$_{1.0}$ (FeSe$_{0.8}$) for $P$$>$3 GPa. A rapid decrease in superconducting volume fraction is observed with an increase in $T_{\rm c}$ above 1.5 GPa, suggesting the presence of electronic inhomogeneity.