Phase Diagram of Pressure-Induced Superconductivity in EuFe2As2 Probed by High-Pressure Resistivity up to 3.2 GPa

Abstract

We have constructed a pressure$-$temperature ($P-T$) phase diagram of $P$-induced superconductivity in EuFe${}_2$As${}_2$ single crystals, via resistivity ($\rho$) measurements up to 3.2 GPa. As hydrostatic pressure is applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at $T_0$ shifts to lower temperatures, and the corresponding resistive anomaly becomes undetectable for $P$ $\ge$ 2.5 GPa. This suggests that the critical pressure $P_{\mathrm{c}}$ where $T_0$ becomes zero is about 2.5 GPa. We have found that the AF order of the Eu${}^{2+}$ moments survives up to 3.2 GPa without significant changes in the AF ordering temperature $T_{\mathrm{N}}$. The superconducting (SC) ground state with a sharp transition to zero resistivity at $T_{\mathrm{c}}$ $\sim$ 30 K, indicative of bulk superconductivity, emerges in a pressure range from $P_{\mathrm{c}}$ $\sim$ 2.5 GPa to $\sim$ 3.0 GPa. At pressures close to but outside the SC phase, the $\rho (T)$ curve shows a partial SC transition (i.e., zero resistivity is not attained) followed by a reentrant-like hump at approximately $T_{\mathrm{N}}$ with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like strain component is applied using a solid pressure medium, the partial superconductivity is continuously observed in a wide pressure range from 1.1 GPa to 3.2 GPa.

7 pages, 6 figures, accepted for publication in Physical Review B, selected as "Editors' Suggestion"