Multiple Transitions of Charge Density Wave Order in Epitaxial Few-Layered 1T′-VTe₂ Films

Abstract

Charge density wave phase comprises a periodic modulation of the electronic charge density with a periodic distortion of the atomic lattice, and transition-metal dichalcogenides are very important subjects for the study of this distortion. In this work, large-area 1T′-vanadium telluride (VTe2) films grown by molecular beam epitaxy show the charge density wave order down to the few-layer limit. The film thickness was found to be strongly correlated with the out-of-plane vibration mode shifting from Raman scattering, and increasing film thickness leads to an insulating-metallic transition. We demonstrate a charge density wave phase transition at 175 K for 2 (ML) films and multiple phase transitions in films more than 5 ML. It was also found that the transition was accompanied with a strong out-of-plane distortion. These findings open up a new window for the search and control of collective phases of two-dimensional VTe2 films.