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arXiv · 1008.1518

Orbital control in strained ultra-thin LaNiO$_3$/LaAlO$_3$ superlattices

J. W. Freeland·Jian Liu·M. Kareev·B. Gray·J. W. Kim·P. Ryan·R. Pentcheva·J. Chakhalian
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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 LaNiO$_3$ and the band insulator LaAlO$_3$. 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 induces octahedral rotations and distortions and altered covalency in the bonding across the interfacial Ni-O-Al apical oxygen, leading to a charge disporportionation at the Ni sites for tensile strain.

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J. W. Freeland, Jian Liu, M. Kareev, B. Gray, J. W. Kim, P. Ryan, R. Pentcheva, J. Chakhalian. 2012-01-20. Orbital control in strained ultra-thin LaNiO$_3$/LaAlO$_3$ superlattices. https://doi.org/10.1209/0295-5075%2F96%2F57004

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