Simultaneous Structural and Electronic Transitions in Epitaxial VO₂/TiO₂(001)

VO₂ is known to undergoes a metal-to-insulator transition (MIT) near room temperature in concomitance with a structural phase transition (SPT) from a rutile to a monoclinic phase. However, the Mott versus Peierls nature of the transition is still under debate. Recently several studies [1] have reported an electron-correlation driven MIT of VO₂ without a corresponding SPT under certain conditions. Here we will present a temperature dependence study [2] of biaxially stretched, epitaxial VO₂ films grown by molecular beam epitaxy on TiO₂(001) employing x-ray standing waves and hard x-ray photoelectron spectroscopy, which are sensitive to the interplanar distance along the V-V dimer direction and the metallicity of VO₂, respectively. This combined study allowed us to monitor simultaneously the MIT and SPT of the strained VO₂ films, which were found to occur concurrently within ±1 K. Comparison of our DFT modelling with the spectroscopic data further supports a cooperative Mott-Peierls description of the transition for VO₂.
[1] E.g., S. Kumar et al., Adv. Mater. 26, 7505 (2014), J. Laverock et al., PRL 113, 216402 (2014), and D. Lee et al., Science 362, 1037 (2018).
[2] G. J. Paez et al., PRL 124, 196402 (2020).