Raman Tensor of WSe2 via Angle-Resolved Polarized Raman Spectroscopy

Tungsten selenide (WSe2) as a van der Waals layered crystal has anisotropic light absorption and light scattering on its out-of-plane surface. However, the Raman tensor of WSe2, which determines the anisotropy of inelastic light scattering, is still unknown without being carefully studied. Here, via establishing angle-resolved polarized Raman spectroscopy measurement, we obtained the experimental Raman tensor of WSe2. Additionally, theoretical Raman tensors under different incident laser line excitations from ultraviolet to infrared were calculated via the first-principles density functional approach, coinciding fairly well with the experimental ones. The first-principles results also reveal that WSe2 has different Raman tensor forms under different laser line excitations, especially the phase difference between Raman tensor elements of the A1g mode. It is suggested that the photon-energy dependent phase differences are determined by the dispersion and absorption of WSe2 on different pump lights.