Graded Orbital Occupation near Interfaces in a La2NiO4 - La2CuO4 Superlattice

TL;DR

This study reveals a tunable, non-uniform distribution of oxygen holes and orbital occupation in a La2NiO4 - La2CuO4 superlattice, with implications for interface engineering in oxide heterostructures.

Contribution

It demonstrates controlled, graded hole doping and orbital occupation variation near interfaces in a superlattice using resonant soft x-ray techniques.

Findings

Oxygen hole distribution is non-uniform and concentrated in LNO layers.

Ni d3z2-r2 orbital occupation varies spatially near interfaces.

Orbital occupation remains stable up to 280 K and is tunable via oxygen interstitials.

Abstract

X-ray absorption spectroscopy and resonant soft x-ray reflectivity show a non-uniform distribution of oxygen holes in a La2NiO4 - La2CuO4 (LNO-LCO) superlattice, with excess holes concentrated in the LNO layers. Weak ferromagnetism with Tc = 160 K suggests a coordinated tilting of NiO6 octahedra, similar to that of bulk LNO. Ni d3z2-r2 orbitals within the LNO layers have a spatially variable occupation. This variation of the Ni valence near LNO-LCO interfaces is observed with resonant soft x-ray reflectivity at the Ni L edge, at a reflection suppressed by the symmetry of the structure, and is possible through graded doping with holes, due to oxygen interstitials taken up preferentially by inner LNO layers. Since the density of oxygen atoms in the structure can be smoothly varied with standard procedures, this orbital occupation, robust up to at least 280 K, is tunable.