Fermi-liquid transport beyond the upper critical field in superconducting La$_2$PrNi$_2$O$_7$ thin films

TL;DR

This study investigates the normal-state transport properties of superconducting La$_2$PrNi$_2$O$_7$ thin films under high magnetic fields, revealing Fermi-liquid behavior and a highly renormalized quasiparticle effective mass, contributing to understanding high-$T_c$ nickelate superconductors.

Contribution

It provides the first detailed magnetotransport characterization of La$_2$PrNi$_2$O$_7$ thin films, demonstrating Fermi-liquid behavior and high effective mass in the normal state of these nickelates.

Findings

Normal state exhibits T^2 resistivity and Hall angle dependence.

Magnetoresistance follows Kohler scaling with H^2 dependence.

Quasiparticle effective mass estimated at approximately 10 times electron mass.

Abstract

Unconventional superconductivity typically emerges out of a strongly correlated normal state, manifesting as a highly renormalized Fermi liquid or a strange metal with $T$-linear resistivity. In Ruddlesden-Popper bilayer nickelates, superconductivity with a critical temperature $T_{\rm c}$ exceeding 80 and 40~K has been respectively realised in pressurized bulk crystals and epitaxially strained thin films. These advancements call for the characterisation of fundamental normal-state and superconducting parameters in these new materials platforms of high-$T_{\rm c}$ superconductivity. Here we report detailed magnetotransport experiments on superconducting La$_2$PrNi$_2$O$_7$ (LPNO) thin films under pulsed magnetic fields up to 64~T and access the normal-state behaviour over a wide temperature range between 1.5 and 300~K. We find that the normal state of thin-film LPNO exhibits the hallmarks of Fermi-liquid transport, including $T^2$ temperature dependence of resistivity and Hall angle, and $H^2$ magnetoresistance obeying Kohler scaling. Using the empirical Kadowaki-Woods ratio, we estimate a quasiparticle effective mass $m^*/m_e \simeq 10$, thereby revealing the highly renormalized Fermi liquid state therein. Our results demonstrate that thin-film LPNO follows the same $T_{\rm c}/T_{\rm F}$ scaling observed across a myriad of strongly correlated superconductors and establish key normal-state characteristics of strained bilayer superconducting nickelates.