Observation of low-frequency Raman peak in layered WTe$_2$

WTe$_2$ recently attracted considerable attention as a layered material exhibiting ferroelectricity, giant magnetoresistance, and pressure-induced superconductivity. In this study, we performed Raman spectroscopy on bulk WTe$_2$, including the unreported low frequency region. A novel Raman peak (P0) was found at approximately 9 cm$^{-1}$ in addition to the seven already known peaks. Furthermore, the angular and polarization dependence of the spectra revealed that the novel peak had $A_1$ symmetry. The existence of this novel peak is consistent with first principles calculations by another group. Our work paves the way for studying the low frequency vibration modes of atomic layer ferrolectric films.