Discerning the Vibrational Nature of ReS₂ Raman Modes Using Solid-Angle-Resolved Raman Spectroscopy

ReS2 exhibits reduced crystal symmetry, which leads to pronounced anisotropy and intricate Raman vibrations. However, to date, the vibrational nature of ReS2 Raman modes has remained elusive, with unresolved theoretical disputes. Here, we study Raman vibrations in ReS2 crystals using solid-angle-resolved Raman spectroscopy, which allows us to leverage the full 3 × 3 Raman tensor to resolve the Ag-like and Eg-like nature of all the 18 Raman modes. Combined with pressure-dependent measurements, we observe distinct behavior in the Ag-like and Eg-like modes. Our findings show unambiguous experimental evidence for discerning the ReS2 Raman modes and can offer important insights into the vibrational nature of Raman modes in layered anisotropic crystals.