Theoretical study on the electronic properties and multiorbital models of La3Ni2O7 thin films on SrLaAlO4 (001)

Abstract

The realization of high-temperature superconductivity in La₃Ni₂O₇ thin films under ambient pressure has triggered a fundamental inquiry into the microscopic origin of the superconducting ground state—specifically, whether the requisite charge carrier density and orbital polarization are induced purely by lattice strain or necessitate an intrinsic charge reconstruction driven by the interface. Here, we employ a systematic density functional theory (DFT + U) investigation of La₃Ni₂O₇/SrLaAlO₄ (001) heterostructures, utilizing a fully self-consistent model that explicitly incorporates substrate-induced compressive strain and interfacial reconstruction. We identify the intrinsic hole doping induced by interfacial Sr interdiffusion as the decisive factor in stabilizing the superconductivity-enabling electronic structure. Crucially, our 1-unit-cell (UC) model naturally reproduces the Fermi surface topology observed in angle-resolved photoemission spectroscopy (ARPES), most notably the critical Ni-d_z² derived γ hole pocket at the Fermi level (E_F). Layer-resolved analysis further reveals that this γ band originates exclusively from the interface-proximal bilayer, suggesting that the interfacial region dominates macroscopic transport. Based on this, we construct a minimal double-stacked two-orbital tight-binding model. Comparative analysis with the bulk phase attributes the reduced superconducting transition temperature (T_c) in thin films to the combined effects of the significantly reduced density of states (DOS) at E_F and the suppression of vertical superexchange coupling (J_⊥^Z), driven by strain-induced out-of-plane lattice expansion. Our findings establish that interface engineering goes beyond mere strain imposition, acting as a decisive factor in modulating nickelate orbital physics.