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

Transition metal dichalcogenide MoTe is an important candidate for realizing the newly predicted type-II Weyl 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 by systematic Raman experiments and first-principles calculations. We identify five lattice vibrational modes that are Raman-active only in the low-temperature noncentrosymmetric structure. 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 phase from vibrational spectroscopy, and suggest MoTe as an ideal candidate for investigating the temperature-induced topological phase transition.