Superconductivity, Electronic Phase Diagram and Pressure Effect in Sr_{1-x}Pr_{x}FBiS_{2}

Abstract

Based on a combination of X-ray diffraction, electrical transports, magnetic susceptibility, specific heat and pressure effect measurements, we report a series of BiS${}_2$-based Sr${}_{1-x}$Pr${}_x$FBiS${}_2$ superconductors with the maximum $T_c$ of 2.7 K for $x=$ 0.5 at ambient pressure. Superconductivity can be only observed at 0.4 $\le$ x $\le$ 0.7 while the normal state resistivity shows the semiconducting-like behaviors. $\chi (T)$ displays the low superconducting shielding volume fractions and $C(T)$ does not exhibit distinguishable anomaly around $T_c$, suggesting a filamentary superconductivity in the Pr-doped polycrystalline samples. By varying doping concentrations, an electrnoic phase diagram can thus be established. Upon applying pressure on the optimal doping Sr${}_{0.5}$Pr${}_{0.5}$FBiS${}_2$ system, $T_c$ is abruptly enhanced, reaches 8.5 K at a critical pressure of $P_c=$ 1.5 GPa and remains a slight increase up to 9.7 K up to 2.5 GPa. Accompanied with the enhancement of superconductivity from the low-$T_c$ phase to the high-$T_c$ phase, the normal state undergoes a semiconductor-to-metal transition under pressure. The scenario can be linked to the enhancement of orbital overlap of Bi-6p and S-p, contributing to the bulk superconductivity above $P_c$. Phase diagram for Sr${}_{0.5}$Pr${}_{0.5}$FBiS${}_2$ is also obtained.

11 pages, 8 figures