Pressure-temperature phase diagram of the ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$ superconductor

The pressure dependencies of the magnetic and superconducting transitions, as well as that of the superconducting upper critical field, are reported for single crystalline ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$. Resistance measurements were performed under hydrostatic pressures up to 6.21 GPa and in magnetic fields up to 9 T. Zero-field-cooled magnetization measurements were performed under hydrostatic pressures up to 1.24 GPa under 20 mT applied field. Superconducting transition temperature, $T_{\text{c}}$, up to 6.21 GPa and magnetic transition temperature, $T_{\text{M}}$, up to 1.24 GPa were obtained and a pressure-temperature phase diagram was constructed. Our results show that $T_{\text{c}}$ is monotonically suppressed upon increasing pressure. $T_{\text{M}}$ is linearly increased up to 1.24 GPa. For the studied pressure range, no signs of the crossing of $T_{\text{M}}$ and $T_{\text{c}}$ lines are observed. The normalized slope of the superconducting upper critical field is gradually suppressed with increasing pressure, which may be due to the continuous change of Fermi velocity $v_F$ with pressure.

Figure 1

(a),(b) Evolution of the in-plane resistance with hydrostatic pressures up to 6.21 GPa measured in a mBAC for ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$ sample 1 and sample 2, respectively. (c),(d) Blowups of the low temperature region showing the superconducting transition. The criterion for $T_{\text{c}}^{\mathrm{offset}}$ is indicated by an arrow in (c).

Figure 2

Pressure dependence of resistance $R\left(p\right)$ at fixed temperatures for ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$ sample 1 (a) and sample 2 (b).

Figure 3

Temperature dependence of resistance under magnetic field up to 9 T for selective pressures for sample 2. Criteria for $T_{\text{c}}^{\mathrm{offset}}$ under magnetic fields are indicated by arrows. Current was applied in-plane and magnetic field was applied along the $c$ axis.

Figure 4

Temperature dependence of the upper superconducting critical field, $H_{\mathrm{c}2}\left(T\right)$, under selected pressures for (a) sample 1 and (b) sample 2.

Figure 5

(a) Evolution of the zero-field-cooled (ZFC) magnetization $M\left(T\right)$ with hydrostatic pressures up to 1.24 GPa under 20 mT applied field. Superconducting transition of Sn is used to determined the low temperature pressure, as indicated by the pink circle. (b) Blowup of the superconducting transition region for ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$. The criterion for $T_{\text{c}}^{\text{onset}}$ is indicated by an arrow. (c) Temperature derivative of the magnetization, $dM/dT$, showing the evolution of the magnetic transition $T_{\text{M}}$. The criterion is indicated by an arrow. The small feature just above 15 K is an artifact caused by the combination of small temperature steps and details of the temperature control in MPMS-3.

Figure 6

(a) Pressure-temperature phase diagram of ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$, as determined from resistance and magnetization measurements. Red and black symbols represent the superconducting $T_{\text{c}}^{\mathrm{offset}}$ and magnetic $T_{\text{M}}$ phase transitions. (b) Pressure dependence of the normalized upper critical field slope $-(1/T_{\mathrm{c}})(d{\mu }_o{H}_{\mathrm{c}2}/dT){|}_{T_{\mathrm{c}}}$. The squares and triangles are data obtained from resistance measurement for sample 1 and sample 2, respectively. The diamonds are data obtained from magnetization measurement. Dashed lines are guides to the eye.

Figure 7

Pressure-temperature phase diagram of ${\mathrm{EuRbFe}}_4{\mathrm{As}}_4$ up to $\sim 30\mathrm{GPa}$, including data from Ref. [27] (open symbols). Open circles corresponds to the onset of the superconducting transition measured via resistivity or magnetic susceptibility. Open triangles corresponds to the magnetic transition determined from magnetic susceptibility or feature in $d\rho /dT$.