Pressure-induced superconductivity in epitaxially-stabilized Pr$_3$Ni$_2$O$_7$ films

TL;DR

This study reports pressure-induced high-temperature superconductivity in epitaxially-stabilized Pr3Ni2O7 thin films, expanding the potential of bilayer nickelates through epitaxial stabilization techniques.

Contribution

It demonstrates that epitaxial stabilization enables the observation of high-Tc superconductivity in Pr3Ni2O7 films under pressure, a significant advancement in nickelate research.

Findings

Superconductivity with Tc up to 66 K at 22 GPa in Pr3Ni2O7 films.

Superconductivity not observed in Nd3Ni2O7 within the measured pressure range.

Epitaxial stabilization allows exploration of Ln ion dependence in bilayer nickelates.

Abstract

The discovery of high critical-temperature $T_{\mathrm{c}}$ superconductivity in La$_3$Ni$_2$O$_7$ under high pressure has led to a rapid expansion of the $T_{\mathrm{c}}$ range through lanthanide $Ln$ substitution, and to ambient-pressure superconductivity in strained thin films, yet the exploration of new bilayer nickelates remains strongly constrained by thermodynamic stability. Beyond the difficulty of synthesis of bulk single-crystals, here we report on the pressure-induced high-$T_{\mathrm{c}}$ superconductivity in epitaxially-stabilized Pr$_3$Ni$_2$O$_7$ thin films. While the Pr$_3$Ni$_2$O$_7$ films exhibit insulating behaviour at ambient pressure regardless of ozone-annealing treatment, they show $T$-linear metallic transport and superconductivity reaching an onset $T_{\mathrm{c}}$ of 66 K and zero-resistance at nearly 40 K at 22 GPa. Furthermore, Nd$_3$Ni$_2$O$_7$, with the smaller rare-earth ion Nd, can also be stabilized, however, superconductivity is not observed in the measured pressure range. Epitaxial stabilization enables us to examine the dependence of $T_{\mathrm{c}}$ and the critical pressure $P_{\mathrm{c}}$ for superconductivity on the $Ln$ ion in $Ln_3$Ni$_2$O$_7$ ($Ln$ = La, Pr, Nd). These results suggest that a higher $P_{\mathrm{c}}$ is required for smaller $Ln$ ions, consistent with trends observed in bulk studies of $Ln$ substitution. This study demonstrates that epitaxial stabilization is a powerful technique to further expand the family of superconducting bilayer nickelates.