Probing single unit-cell resolved electronic structure modulations in oxide superlattices with standing-wave photoemission

TL;DR

This study demonstrates a method combining standing-wave photoemission spectroscopy and electron microscopy to probe the electronic structure of oxide superlattices at a single-unit-cell resolution, revealing layer-specific electronic and structural properties.

Contribution

It introduces a novel approach for depth-resolved, element- and orbital-specific electronic structure analysis at the unit-cell level in complex oxide heterostructures.

Findings

Layer-resolved electronic and chemical state transformations observed.

Experimental results agree with first-principles theoretical calculations.

Method enables future detailed studies of engineered heterostructures.

Abstract

Control of structural couplings at the complex-oxide interfaces is a powerful platform for creating new ultrathin layers with electronic and magnetic properties unattainable in the bulk. However, with the capability to design and control the electronic structure of such buried layers and interfaces at a unit-cell level, a new challenge emerges to be able to probe these engineered emergent phenomena with depth-dependent atomic resolution as well as element- and orbital selectivity. Here, we utilize a combination of core-level and valence-band soft x-ray standing-wave photoemission spectroscopy, in conjunction with scanning transmission electron microscopy, to probe the depth-dependent and single-unit-cell resolved electronic structure of an isovalent manganite superlattice [Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3]x15 wherein the electronic-structural properties are intentionally modulated with depth via engineered oxygen octahedra rotations/tilts and A-site displacements. Our unit-cell resolved measurements reveal significant transformations in the local chemical and electronic valence-band states, which are consistent with the layer-resolved first-principles theoretical calculations, thus opening the door for future depth-resolved studies of a wide variety of hetero-engineered material systems.