Inversion-symmetry-breaking-activated shear Raman bands in $T^{\prime }$-MoTe${}_2$

Abstract

Type-II Weyl fermion nodes, located at the touching points between electron and hole pockets, have been recently predicted to occur in distorted octahedral ($T^{\prime }$) transition metal dichalcogenide semimetals, contingent upon the condition that the layered crystal has the noncentrosymmetric orthorhombic ($T_{or}^{\prime }$) stacking. Here, we report on the emergence of two shear Raman bands activated by inversion symmetry breaking in $T^{\prime }$-MoTe${}_2$ due to sample cooling. Polarization and crystal orientation resolved measurements further point to a phase transition from the monoclinic ($T_{mo}^{\prime }$) structure to the desired $T_{or}^{\prime }$ lattice. These results provide spectroscopic evidence that low-temperature $T^{\prime }$-MoTe${}_2$ is suitable for probing type-II Weyl physics.