Evidence for a reentrant superconducting state in ${\text{EuFe}}_2{\text{As}}_2$ under pressure

We studied the temperature-pressure phase diagram of ${\text{EuFe}}_2{\text{As}}_2$ by electrical resistivity measurements. The spin-density-wave transition at $T_0$ associated with the FeAs-layers is continuously suppressed with increasing pressure, while the antiferromagnetic ordering temperature of the ${\text{Eu}}^{2+}$ moments seems to be nearly pressure independent up to 2.6 GPa. Above 2 GPa a sharp drop of the resistivity, $\rho \left(T\right)$, indicates the onset of superconductivity at $T_c\approx 29.5\text{K}$. Surprisingly, on further reducing the temperature, $\rho \left(T\right)$ is increasing again and exhibiting a maximum caused by the ordering of the ${\text{Eu}}^{2+}$ moments, a behavior which is reminiscent of reentrant superconductivity as it is observed in the ternary Chevrel phases or in the rare-earth nickel borocarbides.

Figure 1

(Color online) Electrical resistivity vs temperature for different applied pressures for single crystalline ${\text{EuFe}}_2{\text{As}}_2$. Inset: $\rho \left(T\right)$ at low temperature for $p=2.03\text{GPa}$ and $p=2.3\text{GPa}$. The superconducting and the antiferromagnetic are marked by arrows.

Figure 2

(Color online) Pressure-temperature phase diagram of ${\text{EuFe}}_2{\text{As}}_2$ obtained from $\rho \left(T\right)$ data. The lines are guides to the eyes.

Figure 3

(Color online) Electrical resistivity at $p=2.16\text{GPa}$ in different magnetic fields. Inset: temperature-magnetic field phase diagram. See text for details.