Cooperative effects of strain and electron correlation in epitaxial VO2 and NbO2
Abstract
We investigate the electronic structure of epitaxial VO2 films in the rutile phase using density functional theory combined with the slave-spin method (DFT + SS). In DFT + SS, multi-orbital Hubbard interactions are added to a DFT-fit tight-binding model, and slave spins are used to treat electron correlations. We find that while stretching the system along the rutile c-axis results in a band structure favoring anisotropic orbital fillings, electron correlations favor equal filling of the t2g orbitals. These two distinct effects cooperatively induce an orbital-dependent redistribution of the electron occupations and spectral weights, driving strained VO2 toward an orbital selective Mott transition (OSMT). The simulated single-particle spectral functions are directly compared to V L-edge resonant X-ray photoemission spectroscopy of epitaxial 10 nm VO2/TiO2 (001) and (100) strain orientations. Excellent agreement is observed between the simulations and experimental data regarding the strain-induced evolution of the lower Hubbard band. Simulations of rutile NbO2 under similar strain conditions are performed, and we predict that an OSMT will not occur in rutile NbO2. Our prediction is supported by the high-temperature hard x-ray photoelectron spectroscopy measurement on relaxed NbO2 (110) thin films with no trace of the lower Hubbard band. Our results indicate that electron correlations in VO2 are important and can be modulated even in the rutile phase before the Peierls instability sets in.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Feb 20, 2019
- Source ID
- 10.1063/1.5052636
Entities
People
- Anna Regoutz
- Christopher N Singh
- D. G. Schlom
- Fanny Rodolakis
- Hanjong Paik
- Jos E. Boschker
- Louis Piper
- Matthew Wahila
- Shantanu Mukherjee
- Tien-lin Lee
- Tyler Eustance
- Wei-Cheng Lee
Organizations
- Air Force Office of Scientific Research
- Argonne National Laboratory
- Binghamton University
- Cornell University
- Diamond Light Source
- Imperial College London
- Indian Institute of Technology Madras
- Leibniz Institute for Crystal Growth
- National Science Foundation
- United States Department of Energy