Theoretical study on the electronic properties and multiorbital models of La${}_3$Ni${}_2$O${}_7$ thin films on SrLaAlO${}_4$ (001)

Abstract

The realization of ambient-pressure superconductivity in La${}_3$Ni${}_2$O${}_7$ thin films raises a fundamental question: is the metallic ground state driven by lattice strain or interfacial charge reconstruction? Using fully self-consistent DFT+$U$ calculations on La${}_3$Ni${}_2$O${}_7$/SrLaAlO${}_4$ heterostructures, we identify that intrinsic hole doping via interfacial Sr interdiffusion is the decisive factor in stabilizing the metallic state. Our 1-unit-cell model accurately reproduces the ARPES-observed Fermi surface, particularly the critical Ni-$d_{z^2}$ derived $\gamma$ hole pocket, which originates exclusively from the interface-proximal bilayer. Furthermore, comparative tight-binding analysis suggests that the reduced superconducting transition temperature ($T_c$) in thin films stems from the synergistic suppression of the electronic density of states (DOS) and vertical superexchange coupling ($J\perp Z$). These findings highlight that interface engineering plays a critical role beyond simple strain imposition in modulating nickelate orbital physics.

18 pages, 6 figures