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I09-Surface and Interface Structural Analysis	Cooperative effects of strain and electron correlation in epitaxial VO2 and NbO2 Wei-Cheng Lee , Matthew Wahila , Shantanu Mukherjee , Christopher N. Singh , Tyler Eustance , Anna Regoutz , Hanjong Paik , Jos E. Boschker , Fanny Rodolakis , Tien-Lin Lee , Darrell G. Schlom , Louis F. J. Piper Journal Of Applied Physics 125 DOI: 10.1063/1.5052636 Diamond Proposal Number(s): [20647, 21430] Show Abstract ▼ Abstract: We investigate the electronic structure of epitaxial VO 2 2 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 c -axis results in a band structure favoring anisotropic orbital fillings, electron correlations favor equal filling of the t 2g t2g orbitals. These two distinct effects cooperatively induce an orbital-dependent redistribution of the electron occupations and spectral weights, driving strained VO 2 2 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 VO 2 2 /TiO 2 2 (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 NbO 2 2 under similar strain conditions are performed, and we predict that an OSMT will not occur in rutile NbO 2 2 . Our prediction is supported by the high-temperature hard x-ray photoelectron spectroscopy measurement on relaxed NbO 2 2 (110) thin films with no trace of the lower Hubbard band. Our results indicate that electron correlations in VO 2 2 are important and can be modulated even in the rutile phase before the Peierls instability sets in.	Feb 2019

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I09-Surface and Interface Structural Analysis

Cooperative effects of strain and electron correlation in epitaxial VO2 and NbO2