VO2 is a model material system which exhibits a metal to insulator transition at 67∘C. This holds potential for future ultrafast switching in memory devices, but typically requires a purely electronic process to avoid the slow lattice response. The role of lattice vibrations is thus important, but it is not well understood and it has been a long-standing source of controversy. We use a combination of ultrafast spectroscopy and ab initio quantum calculations to unveil the mechanism responsible for the transition. We identify an atypical Peierls vibrational mode which acts as a trigger for the transition. This rules out the long standing paradigm of a purely electronic Mott transition in VO2; however, we found a new electron-phonon pathway for a purely reversible electronic transition in a true bi-stable fashion under specific conditions. This transition is very atypical, as it involves purely charge-like excitations and requires only small nuclear displacement. Our findings will prompt the design of future ultrafast electro-resistive non-volatile memory devices.
@article{arxiv.1901.08139,
title = {Possible phonon-induced electronic bi-stability in VO$_2$ for ultrafast memory at room temperature},
author = {Cédric Weber and Swagata Acharya and Brian Cunningham and Myrta Grüning and Liangliang Zhang and Hang Zhao and Yong Tan and Yan Zhang and Cunlin Zhang and Kai Liu and Mark Van Schilfgaarde and Mostafa Shalaby},
journal= {arXiv preprint arXiv:1901.08139},
year = {2020}
}