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Cooperative effects of strain and electron correlation in epitaxial VO 2 and NbO 2

DOI: 10.1063/1.5052636 DOI Help

Authors: Wei-cheng Lee (Binghamton University) , Matthew Wahila (Binghamton University) , Shantanu Mukherjee (Indian Institute of Technology Madras) , Christopher N. Singh (Binghamton University) , Tyler Eustance (Binghamton University) , Anna Regoutz (Imperial College London) , Hanjong Paik (Cornell University) , Jos E. Boschker (Leibniz-Institut für Kristallzüchtung) , Fanny Rodolakis (Argonne National Laboratory) , Tien-lin Lee (Diamond Light Source) , Darrell G. Schlom (Cornell University) , Louis F. J. Piper (Binghamton University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Applied Physics , VOL 125

State: Published (Approved)
Published: February 2019
Diamond Proposal Number(s): 20647 , 21430

Open Access Open Access

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.

Journal Keywords: Epitaxy; X-ray photoelectron spectroscopy; Transition metal oxides; Electronic correlation; Tight-binding model; Phase transitions; Electronic bandstructure; Density functional theory

Subject Areas: Physics, Materials, Chemistry


Instruments: I09-Surface and Interface Structural Analysis