Crossover of Superconductivity across the antiferromagnetic end point in FeSe$_{\rm 1-x}$S$_{\rm x}$ under pressure

TL;DR

This study explores how superconductivity in FeSe$_{1-x}$S$_x$ evolves under pressure, revealing a crossover between two distinct superconducting phases associated with the antiferromagnetic transition.

Contribution

It demonstrates the coexistence and continuous transfer between two superconducting phases across the antiferromagnetic end point under pressure.

Findings

Two superconducting phases coexist within a narrow pressure range.

A continuous transfer of volume fraction occurs between the two SC phases.

Superconductivity crossover is linked with the emergence of AFM phase.

Abstract

Temperature-pressure ($T$-$P$) phase diagrams of FeSe$_{\rm 1-x}$S$_{\rm x}$ were investigated by the measurements of dc magnetization ($M$) and electrical resistivity ($\rho$) under pressure, using single crystal specimens with $x$=0.04, 0.08 and 0.13. For all specimens, the $M$($T$) curves under pressure near the end point of the antiferromagnetic (AFM) phase are found to show a two-step diamagnetic response, which can be described as the sum of two diamagnetic components $M_1$($T$) and $M_2$($T$), indicating that two superconducting (SC) phases with different $T_{\rm c}$ values coexist within a pressure range of $\Delta$$P$$\sim$1 GPa. Moreover, the pressure dependence of the amplitudes of $M_1$($T$) and $M_2$($T$) indicates a continuous transfer of the volume fraction between the two SC phases. These behaviors suggest that a crossover of superconductivity occurs in conjunction with the emergence of AFM phase and imply that the SC phases inside and outside the AFM phase could have different origins.