Activation of new Raman modes by inversion symmetry breaking in type II Weyl semimetal candidate T'-MoTe2

Abstract

We synthesized distorted octahedral(T') molybdenum ditelluride (MoTe2) and investigated its vibrational properties with Raman spectroscopy, density functional theory and symmetry analysis. Compared to the results from high temperature centrosymmetric monoclinic (T'mo) phase, four new Raman bands emerge in the low temperature orthorhombic (T'or) phase, which was recently predicted to be a type II Weyl semimetal. Crystal-angle-dependent, light-polarization-resolved measurements indicate that all the observed Raman peaks belong to two categories: those vibrating along the zigzag Mo atomic chain (z-mode) and those vibrating in the mirror plane (m-mode) perpendicular to the zigzag chain. Interestingly the low energy shear z-mode and shear m-mode, absent from the T'mo spectra, become activated when sample cooling induces a phase transition to the T'or crystal structure. We interpret this observation as a consequence of inversion-symmetry breaking, which is crucial for the existence of Weyl fermions in the layered crystal. Our temperature dependent Raman measurements further show that both the high energy m-mode at 130 cm-1 and the low energy shear m-mode at 12 cm-1 provide useful gauges for monitoring the broken inversion symmetry in the crystal.

Incorporates earlier results presented in arXiv:1602.03566 entitled as Inversion-symmetry-breaking-activated shear Raman bands in T'-MoTe2

References in corpus (4)

• Quantum Spin Hall Effect and Topological Field Effect Transistor in Two-Dimensional Transition Metal Dichalcogenides
• Helicity resolved Raman scattering of MoS2, MoSe2, WS2 and WSe2 atomic layers
• Observation of interlayer phonon modes in van der Waals heterostructures
• Testing several recent van der Waals density functionals for layered structures

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