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

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 ($ρ$) 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 $Δ$$P$$\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.