Dimensionality Control of d-orbital Occupation in Oxide Superlattices

TL;DR

This study demonstrates precise control of d-orbital occupancy in oxide superlattices, revealing a transition from Mott insulator to band insulator as the LaCoO3 layer thickness approaches one unit cell, unaffected by epitaxial strain.

Contribution

It provides a clear experimental demonstration of orbital occupancy control in oxide superlattices, highlighting the impact of dimensionality on electronic structure without strain influence.

Findings

Transition from Mott insulator to band insulator with decreasing LaCoO3 thickness

Complete filling of t2g orbitals and emptying of eg orbitals at one unit-cell thickness

Orbital control is insensitive to epitaxial strain

Abstract

Manipulating the orbital state in a strongly correlated electron system is of fundamental and technological importance for exploring and developing novel electronic phases. Here, we report an unambiguous demonstration of orbital occupancy control between t2g and eg multiplets in quasi-twodimensional transition metal oxide superlattices (SLs) composed of a Mott insulator LaCoO3 and a band insulator LaAlO3. As the LaCoO3 sublayer thickness approaches its fundamental limit (i.e. one unit-cell-thick), the electronic state of the SLs changed from a Mott insulator, in which both t2g and eg orbitals are partially filled, to a band insulator by completely filling (emptying) the t2g (eg) orbitals. We found the reduction of dimensionality has a profound effect on the electronic structure evolution, which is, whereas, insensitive to the epitaxial strain. The remarkable orbital controllability shown here offers a promising pathway for novel applications such as catalysis and photovoltaics, where the energy of d level is an essential parameter.