Nature of the metal-insulator transition in few-unit-cell-thick LaNiO<sub>3</sub> films.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 29880888.
- Also identified by DOI 10.1038/s41467-018-04546-5 and PMC identifier 5992201.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The nature of the metal-insulator transition in thin films and superlattices of LaNiO<sub>3</sub> only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate-film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO<sub>3</sub> films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO<sub>3</sub> substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO<sub>2</sub> termination). Electronic structure measurements using X-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal-insulator transition.