Cooperative Effects of Strain and Electron Correlation in Epitaxial VO2 and NbO2

Wei-Cheng Lee; Matthew J. Wahila; Shantanu Mukherjee; Christopher N. Singh; Tyler Eustance; Anna Regoutz; H. Paik; Jos E. Boschker; Fanny Rodolakis; Tien-Lin Lee; D. G. Schlom; Louis F. J. Piper

doi:10.1063/1.5052636

paper

Cooperative Effects of Strain and Electron Correlation in Epitaxial VO2 and NbO2

arXiv:1808.07063 · doi:10.1063/1.5052636

Abstract

We investigate the electronic structure of the epitaxial VO $_{2}$ films in the rutile phase using the density functional theory combined with the slave spin method (DFT+SS). In DFT-SS, the multiorbital Hubbard interactions are added to a DFT-fit tight-binding model, and we employ the slave-spin method to treat the electron correlation. We find that while stretching the system along the rutile $c$ -axis results in a band structure favoring an anisotropic orbital fillings, the electron correlation favors an equal electron filling among $t_{2 g}$ orbitals. These two distinct effects cooperatively induce interesting orbital-dependent redistributions of the electron occupations and the spectral weights, which pushes the strained VO $_{2}$ 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 $_{2}$ /TiO $_{2}$ (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 $_{2}$ under similar strain conditions as VO $_{2}$ are performed, and we predict that OSMT will not occur in rutile NbO $_{2}$ . Our results indicates that the electron correlation in VO $_{2}$ is important and can be modulated even in the rutile phase before the Peierls instability sets in.

8 pages, 9 figures, invited paper for Special Topic: Strain Engineering in Functional Materials by Journal of Applied Physics