Activation of New Raman Modes by Inversion Symmetry Breaking in Type II Weyl Semimetal Candidate T′-MoTe2

Shao Yu Chen, Thomas Goldstein, Dhandapani Venkataraman, Ashwin Ramasubramaniam, Jun Yan

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56 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)5852-5860
Number of pages9
JournalNano Letters
Volume16
Issue number9
DOIs
Publication statusPublished - 14 Sep 2016
Externally publishedYes

Keywords

  • inversion symmetry breaking
  • molybdenum ditelluride
  • phase transition
  • Raman scattering
  • Transition metal dichalcogenides
  • Weyl semimetal

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