Angle and Polarization-Resolved Resonant Raman Spectroscopy of the Type-II Weyl Semimetal NbIrTe₄

We perform polarized Raman spectroscopy measurements of single nanoflakes exfoliated from a single crystal of the layered ternary compound NbIrTe₄. By varying the angle between the polarization direction of incident light and the crystalline “a” axis, spectra indicate strongly anisotropic Raman peaks which are consistent with the broken inversion symmetry of the crystal, which is an essential enabling condition for a type II Weyl semimetal. We have used both 633 nm and 514 nm laser excitation with incoming and backscattered rays parallel to the c-axis normal to the flake with the “a” and “b” axes in the plane of the nanoflake. The comparison of these spectra shows an enhancement of Raman peaks and also changes in rotational symmetry for 633 nm excitation. This suggest a possible unresolved resonance with a state at lower energies. Density Functional Theory (DFT) calculations of this crystal (space group Pmn2₁) show close correspondence with both the frequency and symmetries of the modes detected in our measurement.