Temperature-pressure ($T-P$) phase diagrams of ${\mathrm{FeSe}}_{1-\mathrm{x}}{\mathrm{S}}_{\mathrm{x}}$ 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 $T_{\mathrm{c}}$ values coexist within a pressure range of $\mathrm{\Delta }P\sim 1\mathrm{GPa}$. 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.

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• Crystal growth
• Pairing mechanisms
• Phase diagrams
• Pressure effects
• Iron-based superconductors
• Layered crystals
• Single crystal materials
• Unconventional superconductors
• Magnetization measurements
• Pressure techniques
• Resistivity measurements