Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures

TL;DR

This study reveals a unique interfacial band in NdNiO3/STO heterostructures caused by orbital hybridization, significantly affecting their electronic properties and offering new ways to tune oxide interfaces.

Contribution

It uncovers the orbital hybridization mechanism leading to a new interfacial band in NdNiO3/STO heterostructures through combined experimental and theoretical analysis.

Findings

Identification of a new unoccupied interfacial band above the Fermi level.

Orbital hybridization between Ti 3d and O 2p orbitals drives the band formation.

Detection of exciton peaks indicating strong electron-electron and electron-hole interactions.

Abstract

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 thin films grown on a series of single crystal substrates. Unlike films synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure which features an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by the orbital hybridization between Ti 3d orbitals of the STO substrate and O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin-films, thereby offering key insights into tuning their interfacial properties.