Non-Fermi liquid behavior in La$_3$Ni$_2$O$_7$ thin films under hydrostatic pressure

Abstract: The discovery of superconductivity in bilayer nickel-oxides has revived an intense effort to understand the potential of high-temperature superconductivity in these materials and their relation to cuprate superconductors. In this work, we investigate the growth and properties of bilayer La$_3$Ni$_2$O$_7$ thin films as a function of substrate, oxygen treatment and applied pressure in order to study the evolution of transport properties. We report epitaxial growth of La$_3$Ni$_2$O$_7$ thin films on LaAlO$_3$ (LAO) (001) and SrLaAlO$_4$ (SLAO) (001) substrates, and the effects of ex-situ annealing in a high pressure furnace under an oxygen-rich environment. Transport measurements show that the La$_3$Ni$_2$O$_7$ thin films on LAO(001) exhibit Fermi liquid-like metallic behavior with a slight Kondo-like upturn at low temperatures, which evolves with the application of modest hydrostatic pressures toward non-Fermi liquid behavior with a temperature dependence of resistance approaching $\sim$ T$^{1.4}$ at 1.41 GPa. The ability to tune the normal state resistivity of La$_3$Ni$_2$O$_7$ films to display non-Fermi liquid behavior under such a modest hydrostatic pressure range - only 6 - 8 % of that typically applied via diamond anvil cell (DAC) in La$_3$Ni$_2$O$_7$ single crystals to achieve comparable effects - is both noteworthy and unexpected. These findings imply the strong tunability of La$_3$Ni$_2$O$_7$ in thin film form and the likely proximity of a strongly fluctuating ordered state leading to non-Fermi liquid behavior under even modest applied pressures.