Reducing orbital occupancy in VO2 suppresses Mott physics while Peierls distortions persist

Abstract

The characteristics of the cooperative Mott-Peierls metal-insulator transition (MIT) of ${\mathrm{VO}}_{2}$ can be altered by employing epitaxial strain. While the most commonly used substrate for this purpose is isostructural rutile ${\mathrm{TiO}}_{2}$, thin films often suffer from interdiffusion of Ti ions near the interface. Exploiting this phenomena, we investigate the nature of interfacial ${\mathrm{V}}^{4+}/{\mathrm{Ti}}^{4+}$ cation intermixing and its effects on the MIT using scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS), soft x-ray absorption spectroscopy (XAS), and hard x-ray photoelectron spectroscopy (HAXPES), along with supporting density functional theory (DFT) calculations. We find that the reduced orbital occupancy in highly Ti incorporated ${\mathrm{VO}}_{2}$ is responsible for suppressing the MIT. Interdiffused films are found to be metallic at all measured temperatures, despite a resolute dimerization inferred from x-ray absorption data at lower temperatures. Our results demonstrate that the Mott physics can be suppressed in doped ${\mathrm{VO}}_{2}$, while a lattice dimerization remains thermodynamically favorable.