Unveiling the microscopic dynamics of the charge density wave transition in monolayer VX2 (X=S, Te)

Abstract

Charge density waves (CDWs) in two-dimensional materials have received great attention due to their intriguing properties, yet the microscopic evolution process of CDW transition and its impact on charge transport remain to be fully understood. Herein we employed density-functional theory calculations to ascertain the richness of CDW phases in $\mathrm{V}{X}_2$ ($X=\mathrm{S}$, Te) originated from electron-phonon coupling. Reversible transitions between the normal and CDW phases are directly simulated with ab initio molecular dynamics, indicating that the formation of CDW phase is a rapid nucleation process. The corresponding microscopic dynamic processes involve the formation, flipping, translation, and aggregation of characteristic patterns, which are driven by the soft phonon modes. Modifications of electrical conductivity in CDW phase transition are found to stem from the varying orientation and location distributions of relevant wave functions. The revealed dynamic mechanism opens an opportunity for the control of CDW phase transition that is crucial to its applications in logical circuits and neural networks.