Polarized Raman Spectroscopy of 2H‐NbSe 2 and 1T‐VSe 2 Single Crystals

This is the authors' abstract. We don't add key points for this paper.

We present the polarized Raman spectra of 2H‐NbSe and 1T‐VSe single crystals. The phonon symmetries of the first‐order Raman‐active modes in both materials are identified using linearly and circularly polarized Raman spectroscopy. In particular, the Raman peak of 1T‐VSe at 250 cm , previously assigned to the E mode, is reinterpreted as two‐phonon combinational modes at the M point in the Brillouin zone. The helicity‐dependent Raman spectroscopy enables the separation of the overlapping A and E modes in 2H‐NbSe . The second‐order phonon modes exhibit either helicity‐conserving or helicity‐changing behavior. The first‐principles calculations of phonon dispersion and the two‐phonon density of states support the assignment of the two‐phonon modes. The calculated shear and layer breathing modes of 2H‐NbSe appear at 37 and 53 cm , respectively, while the calculated E mode of 1T‐VSe appears at 139 cm .