Phase diagram of infinite layer praseodymium nickelate ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films

We report the phase diagram of infinite layer ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films synthesized via topotactic reduction from the perovskite precursor phase using ${\mathrm{CaH}}_2$. Based on the electrical transport properties, we find a doping-dependent superconducting dome extending between $x=0.12$ and 0.28 with a maximum superconducting transition temperature $T_{\mathrm{c}}$ of 14 K at $x=0.18$, bounded by weakly insulating behavior on both sides. In contrast to the narrower dome observed in ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$, a local $T_{\mathrm{c}}$ suppression near $x=0.2$ was not observed for the ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ system. Normal-state Hall effect measurements indicate mixed carrier contributions of both electrons and holes and show a sign change in the Hall coefficient as functions of temperature and $x$, quite similar to that in ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$. Also similar is the observation of a minimum in the normal-state resistivity associated with the superconducting compositions. These findings indicate an infinite layer nickelate phase diagram that is relatively insensitive to the rare-earth element but suggest that disorder arising from the variations of the ionic radii on the rare-earth site affects the superconducting dome.

Figure 1

(a) X-ray diffraction $\theta \text{−}2\theta$ symmetric scans of ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films grown on ${\mathrm{SrTiO}}_3$ (001) substrates. (b) The atomic structure of the infinite-layer ${\mathrm{PrNiO}}_2$. (c) Lattice constants and unit-cell volumes of ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films. The unit-cell volume of thin-film ${\mathrm{NdNiO}}_2$ is shown as a reference [46]. (d) Reciprocal space maps around the $\overline{1}03$ peaks. All scans were performed at room temperature.

Figure 2

(a) Representative temperature dependence of resistivity $\rho$-T curves for ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films. (b) The enlarged $\rho$-T curves in the temperature range from 2 to 40 K. (c) The phase diagram of ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films. Closed and open circles represent $T_{\mathrm{c},90\%R}$ and $T_{\mathrm{c},10\%R}$ as defined to be the temperatures at which the resistivity is 90% and 10% of the resistivity value at 20 K, respectively. The dashed line indicates the minimum measurement temperature 2 K. The inset shows the phase diagram of ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films adapted from Ref. [46].

Figure 3

(a) Normal-state Hall coefficient as a function of temperature for ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films. (b) Hall coefficient $R_{\mathrm{H}}$ and resistivity $\rho$ as a function of Sr $x$ at 20 K (top and bottom, respectively). Triangles and circles represent ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ [46] and ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$, respectively. The superconducting dome of ${\mathrm{Pr}}_{1-x}{\mathrm{Sr}}_x{\mathrm{NiO}}_2$ thin films is shown in the background of the lower panel.