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

TL;DR

This study maps the pressure-temperature phase diagram of EuFe2As2, revealing the emergence of bulk superconductivity around 2.5 GPa and its dependence on pressure conditions, with detailed insights into magnetic and superconducting transitions.

Contribution

The paper provides the first detailed pressure-temperature phase diagram of EuFe2As2 up to 3.2 GPa, highlighting the pressure range for bulk superconductivity and the effects of hydrostatic versus nonhydrostatic pressure conditions.

Findings

Superconductivity emerges around 2.5 GPa with a transition temperature of ~30 K.

Antiferromagnetic order of Eu2+ persists up to 3.2 GPa without significant change.

Partial superconductivity observed over a wide pressure range under nonhydrostatic conditions.

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 $T_\mathrm{0}$ 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 $T_\mathrm{0}$ 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.