Transition metal oxides such as vanadium dioxide (VO2), niobium dioxide (NbO2), and titanium sesquioxide (Ti2O3) 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 VO2 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 d1 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.
@article{arxiv.2012.05306,
title = {The Breakdown of Mott Physics at VO$_2$ Surfaces},
author = {Matthew J. Wahila and Nicholas F. Quackenbush and Jerzy T. Sadowski and Jon-Olaf Krisponeit and Jan Ingo Flege and Richard Tran and Shyue Ping Ong and Christoph Schlueter and Tien-Lin Lee and Megan E. Holtz and David A. Muller and Hanjong Paik and Darrell G. Schlom and Wei-Cheng Lee and Louis F. J. Piper},
journal= {arXiv preprint arXiv:2012.05306},
year = {2020}
}