The metal-insulator transition (MIT) in vanadium dioxide VO2 due to V-V dimerization has been extensively discussed for decades. While it is widely acknowledged that electron correlations, Peierls instabilities, and molecular orbital formations are crucial for understanding the MIT of VO2, the primary origin of the MIT remains controversial. In this study, we delve into the crystal structure and orbital state of VO2 through synchrotron x-ray diffraction experiments. The molecular orbital formation corresponding to the V-V dimerization is directly observed in the low-temperature insulating monoclinic phase, called the M1 phase, as indicated by the valence electron density distribution. Moreover, diffuse scattering observed in the high-temperature metal phase of rutile structure suggests the presence of short-range correlation of V displacements, which is not directly attributed to the structural fluctuation of the M1 phase. The short-range order in the rutile phase will be the key to understanding the MIT in this system.
@article{arxiv.2310.10193,
title = {Molecular orbital formation and metastable short-range ordered structure in VO$_2$},
author = {Shunsuke Kitou and Akitoshi Nakano and Masato Imaizumi and Yuiga Nakamura and Ichiro Terasaki and Taka-hisa Arima},
journal= {arXiv preprint arXiv:2310.10193},
year = {2024}
}