title: 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 results from the 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-modes) and those vibrating in the mirror plane (m-modes) 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.
authors: Department of Physics, ‡Department of Chemistry, and §Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
authors: Shao-Yu
authors: SY
authors: Chen
authors: Department of Physics, ‡Department of Chemistry, and §Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
authors: Thomas
authors: T
authors: Goldstein
authors: Department of Physics, ‡Department of Chemistry, and §Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
authors: Dhandapani
authors: D
authors: Venkataraman
authors: Department of Physics, ‡Department of Chemistry, and §Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
authors: Ashwin
authors: A
authors: Ramasubramaniam
authors: Department of Physics, ‡Department of Chemistry, and §Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
authors: Jun
authors: J
authors: Yan
keywords: Raman scattering; Transition metal dichalcogenides; Weyl semimetal; inversion symmetry breaking; molybdenum ditelluride; phase transition