Raman signatures of inversion symmetry breaking and structural phase transition in type-II Weyl semimetal MoTe2

TL;DR

This study provides direct spectroscopic evidence of inversion symmetry breaking and a structural phase transition in MoTe$_2$, highlighting its potential for exploring topological phase changes and Weyl fermions.

Contribution

The paper combines Raman spectroscopy and first principles calculations to definitively identify the noncentrosymmetric low-temperature phase of MoTe$_2$ and its associated phase transition.

Findings

Identification of five Raman-active modes exclusive to the noncentrosymmetric phase

Observation of hysteresis in Raman peak intensities indicating a phase transition

Confirmation of temperature-induced structural change affecting inversion symmetry

Abstract

Transition metal dichalcogenide MoTe$_2$ is an important candidate for realizing the newly predicted type-IIWeyl fermions, for which the breaking of the inversion symmetry is a prerequisite. Here we present direct spectroscopic evidence for the inversion symmetry breaking in the low temperature phase of MoTe$_2$ by systematic Raman experiments and first principles calculations. We identify five lattice vibrational modes which are Raman active only in noncentrosymmetric structure at low temperature. A hysteresis is also observed in the peak intensity of inversion symmetry activated Raman modes, confirming a temperature induced structural phase transition with a concomitant change in the inversion symmetry. Our results provide definitive evidence for the low temperature noncentrosymmetric T$_d$ phase from vibrational spectroscopy, and suggest MoTe$_2$ as an ideal candidate for investigating the temperature induced topological phase transition.