  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.
