Fermi-liquid transport beyond the upper critical field in superconducting La₂PrNi₂O₇ thin films.

Abstract

Unconventional superconductivity typically emerges out of a strongly correlated normal state, manifesting as a highly renormalised Fermi liquid or a strange metal with T-linear resistivity. In Ruddlesden-Popper bilayer nickelates, superconductivity with a critical temperature T_c exceeding 80 and 40 K has been respectively realised in pressurised 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_c superconductivity. Here we report detailed magnetotransport experiments on superconducting La₂PrNi₂O₇ (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 T² temperature dependence of resistivity and Hall angle, and H² magnetoresistance obeying Kohler scaling. Using the empirical Kadowaki-Woods ratio, we estimate a quasiparticle effective mass m^*/m_e ≃ 10, thereby revealing the highly renormalised Fermi liquid state therein. Our results demonstrate that thin-film LPNO follows the same T_c/T_F scaling observed across a myriad of strongly correlated superconductors and establish key normal-state characteristics of strained bilayer superconducting nickelates.