Evidence for two distinct superconducting phases in EuBiS${}_2$F under pressure

Abstract

We present a pressure study of the electrical resistivity, AC magnetic susceptibility and powder x-ray diffraction (XRD) of the newly discovered BiS${}_2$-based superconductor EuBiS${}_2$F. At ambient pressure, EuBiS${}_2$F shows an anomaly in the resistivity at around $T_0\approx 280$ K and a superconducting transition at $T_c\approx 0.3$ K. Upon applying hydrostatic pressure, there is little change in $T_0$ but the amplitude of the resistive anomaly is suppressed, whereas there is a dramatic enhancement of $T_c$ from 0.3 K to about 8.6 K at a critical pressure of $p_c$ $\approx 1.4$ GPa. XRD measurements confirm that this enhancement of $T_c$ coincides with a structural phase transition from a tetragonal phase ($P4/nmm$) to a monoclinic phase ($P{2}_1$/m), which is similar to that observed in isostructural LaO${}_{0.5}$F${}_{0.5}$BiS${}_2$. Our results suggest the presence of two different superconducting phases with distinct crystal structures in EuBiS${}_2$F, which may be a general property of this family of BiS${}_2$-based superconductors.

5 pages, 5 figures