Orbital control in strained ultra-thin LaNiO3/LaAlO3 superlattices

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Published 22 November 2011 Europhysics Letters Association
, , Citation J. W. Freeland et al 2011 EPL 96 57004 DOI 10.1209/0295-5075/96/57004

0295-5075/96/5/57004

Abstract

In pursuit of rational control of orbital polarization, we present a combined experimental and theoretical study of single-unit-cell superlattices of the correlated metal LaNiO3 and the band insulator LaAlO3. Polarized X-ray absorption spectra show a distinct asymmetry in the orbital response under strain. A splitting of orbital energies consistent with octahedral distortions is found for the case of compressive strain. In sharp contrast, for tensile strain, no splitting is found although a strong orbital polarization is present. Density functional theory calculations including a Hubbard U-term reveal that this asymmetry is a result of the interplay of strain and confinement that induces octahedral rotations and distortions and altered covalency in the bonding across the interfacial Ni-O-Al apical oxygen, leading to a charge disproportionation at the Ni sites for tensile strain.

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10.1209/0295-5075/96/57004