Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO${}_3$/SrTiO${}_3$ Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission

Abstract

LaNiO${}_3$ (LNO) is an intriguing member of the rare-earth nickelates in exhibiting a metal-insulator transition for a critical film thickness of about 4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such thin films also show a transition to a metallic state in superlattices with SrTiO${}_3$ (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to better understand this transition, we have studied a strained LNO/STO superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an (LaAlO${}_3$)${}_{0.3}$(Sr${}_2$AlTaO${}_6$)${}_{0.7}$ substrate using soft x-ray standing-wave-excited angle-resolved photoemission (SWARPES), together with soft- and hard- x-ray photoemission measurements of core levels and densities-of-states valence spectra. The experimental results are compared with state-of-the-art density functional theory (DFT) calculations of band structures and densities of states. Using core-level rocking curves and x-ray optical modeling to assess the position of the standing wave, SWARPES measurements are carried out for various incidence angles and used to determine interface-specific changes in momentum-resolved electronic structure. We further show that the momentum-resolved behavior of the Ni 3d eg and t2g states near the Fermi level, as well as those at the bottom of the valence bands, is very similar to recently published SWARPES results for a related La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$/SrTiO${}_3$ superlattice that was studied using the same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which further validates this experimental approach and our conclusions. Our conclusions are also supported in several ways by comparison to DFT calculations for the parent materials and the superlattice, including layer-resolved density-of-states results.

References in corpus (13)

• Unveiling a two-dimensional electron gas with universal subbands at the surface of SrTiO3
• Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface
• Orbital order and possible superconductivity in LaNiO3/LaMO3 superlattices
• Profiling the interface electron gas of LaAlO3/SrTiO3 heterostructures by hard X-ray photoelectron spectroscopy
• Turning a nickelate Fermi surface into a cuprate-like one through heterostructuring
• Quantum confinement of Mott electrons in ultrathin LaNiO3/LaAlO3 superlattice
• Metal-insulator transition in a two-band model for the perovskite nickelates
• Fermi surfaces, electron-hole asymmetry and correlation kink in a three-dimensional Fermi liquid LaNiO${}_3$
• Structural origins of the properties of rare earth nickelate superlattices
• Confinement-induced metal-to-insulator transition in strained LaNiO${}_3$/LaAlO${}_3$ superlattices
• Evidence for mass renormalization in LaNiO$"" sub 3_: an in situ soft x-ray photoemission study of epitaxial films
• Energetic, spatial and momentum character of a buried interface: the two-dimensional electron gas between two metal oxides
• Momentum-resolved electronic structure at a buried interface from soft x-ray standing-wave angle-resolved photoemission

Cited by in corpus (5)

• Design of $n$- and $p$-type oxide thermoelectrics in LaNiO${}_3$/SrTiO${}_3(001)$ superlattices exploiting interface polarity
• Electronic Structure of the Dilute Magnetic Semiconductor $G{a}_{1-x}M{n}_{x}P$ from Hard X-ray Photoelectron Spectroscopy and Hard X-ray Angle-Resolved Photoemission
• Observation of Wannier-Stark localization at the surface of BaTiO${}_3$ films by photoemission
• Emergent phenomena at oxide interfaces studied with standing-wave photoelectron spectroscopy
• An Efficient Algorithm for Automatic Structure Optimization in X-ray Standing-Wave Experiments