Orbital reflectometry

TL;DR

This paper introduces a method to quantitatively measure orbital polarization profiles at surfaces and interfaces of transition metal oxides using soft x-ray reflectivity, enabling atomic-scale insights into orbital physics.

Contribution

It presents a novel, model-independent technique to derive spatially resolved orbital polarization profiles from soft x-ray reflectivity data.

Findings

Successfully measured 3% differences in Ni e_g orbital occupation in superlattice layers.

Method shows good agreement with ab-initio electronic-structure calculations.

Enables direct correlation between theory and experiment at the atomic scale.

Abstract

The occupation of d-orbitals controls the magnitude and anisotropy of the inter-atomic electron transfer in transition metal oxides and hence exerts a key influence on their chemical bonding and physical properties. Atomic-scale modulations of the orbital occupation at surfaces and interfaces are believed to be responsible for massive variations of the magnetic and transport properties, but could thus far not be probed in a quantitative manner. Here we show that it is possible to derive quantitative, spatially resolved orbital polarization profiles from soft x-ray reflectivity data, without resorting to model calculations. We demonstrate that the method is sensitive enough to resolve differences of 3 % in the occupation of Ni e_g orbitals in adjacent atomic layers of a LaNiO3-LaAlO3 superlattice, in good agreement with ab-initio electronic-structure calculations. The possibility to quantitatively correlate theory and experiment on the atomic scale opens up many new perspectives for orbital physics in d-electron materials.