Anomalous Raman scattering and lattice dynamics in mono- and few-layer WTe2

Abstract

Tungsten ditelluride (WTe₂) is a layered material that exhibits excellent magnetoresistance and thermoelectric behaviors, which are deeply related with its distorted orthorhombic phase that may critically affect the lattice dynamics of this material. Here, we report comprehensive characterization of Raman spectra of WTe₂ from bulk to monolayer using experimental and computational methods. We find that mono and bi-layer WTe₂ are easily identified by Raman spectroscopy since two or one Raman modes that are observed in higher-layer WTe₂ are greatly suppressed below the noise level in the mono- and bi-layer WTe₂, respectively. In addition, the frequency of in-plane A₁⁷ mode of WTe₂ remains almost constant as the layer number decreases, while all the other Raman modes consistently blueshift, which is completely different from the vibrational behavior of hexagonal metal dichalcogenides. First-principles calculation validates experimental results and reveals that anomalous lattice vibrations in WTe₂ are attributed to the formation of tungsten chains that make WTe₂ structurally one-dimensional.