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

TL;DR

This study uses first-principles calculations to show that interfacial hole doping, rather than strain, stabilizes the metallic state in La$_3$Ni$_2$O$_7$ thin films, influencing their electronic properties and superconductivity.

Contribution

It provides a detailed theoretical analysis revealing the role of interfacial doping and electronic structure in La$_3$Ni$_2$O$_7$ thin films, advancing understanding of their superconducting behavior.

Findings

Interfacial Sr interdiffusion causes hole doping, stabilizing metallicity.

The model reproduces ARPES Fermi surface features, especially the Ni-$d_{z^2}$ hole pocket.

Reduced $T_c$ is linked to suppressed DOS and superexchange coupling.

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.