The Breakdown of Mott Physics at VO$_2$ Surfaces

TL;DR

This study reveals that surface termination suppresses the bulk structural transition in VO$_2$, altering its Mott physics and electronic structure, with implications for understanding and applying transition metal oxides.

Contribution

It demonstrates that surface reconstructions prevent the bulk structural transition in VO$_2$, providing new insights into surface effects on Mott insulators and their device applications.

Findings

Suppression of bulk structural transition at VO$_2$ surfaces

Surface reconstructions alter electronic structure from bulk properties

Implications for characterization and device use of Mott-like materials

Abstract

Transition metal oxides such as vanadium dioxide (VO$_2$), niobium dioxide (NbO$_2$), and titanium sesquioxide (Ti$_2$O$_3$) are known to undergo a temperature-dependent metal-insulator transition (MIT) in conjunction with a structural transition within their bulk. However, it is not typically discussed how breaking crystal symmetry via surface termination affects the complicated MIT physics. Using synchrotron-based x-ray spectroscopy, low energy electron diffraction (LEED), low energy electron microscopy (LEEM), transmission electron microscopy (TEM), and several other experimental techniques, we show that suppression of the bulk structural transition is a common feature at VO$_2$ surfaces. Our density functional theory (DFT) calculations further suggest that this is due to inherent reconstructions necessary to stabilize the surface, which deviate the electronic structure away from the bulk d$^1$ configuration. Our findings have broader ramifications not only for the characterization of other "Mott-like" MITs, but also for any potential device applications of such materials.