Pressure-Induced Phase Transition in La$_{1-x}$Sm$_{x}$O$_{0.5}$F$_{0.5}$BiS$_2$

摘要

Electrical resistivity measurements onLa$_{1-x}$Sm$_{x}$O$_{0.5}$F$_{0.5}$BiS$_{2}$ ($x$ = 0.1, 0.3, 0.6, 0.8) havebeen performed under applied pressures up to 2.6 GPa from 2 K to roomtemperature. The superconducting transition temperature $T$$_{c}$ of eachsample significantly increases at a Sm-concentration dependent pressure$P$$_{\rm t}$, indicating a pressure-induced phase transition from alow-$T$$_{c}$ to a high-$T$$_{c}$ phase. The compounds that have higher Smconcentrations have higher $T$$_{c}$ values at ambient pressure; however, the$T$$_{c}$ values at $P$ $>$ $P$$_{\rm t}$ decrease with $x$ and $P$$_{\rm t}$shifts to higher pressures with Sm substitution. In the normal state,semiconducting-like behavior is suppressed and metallic conduction is inducedwith increasing pressure in all of the samples. These results suggest that thepressure dependence of $T$$_{c}$ for the BiS$_{2}$-based superconductors isrelated to the lattice parameters at ambient pressure and enable us to estimatethe evolution of $T$$_{c}$ for SmO$_{0.5}$F$_{0.5}$BiS$_{2}$ under pressure.