Raman scattering study of two-dimensional magnetic van der Waals compound VI3

The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research. Previous x-ray diffraction (XRD) studies on the magnetic van der Waals compound VI3, revealed a structural transition above the magnetic transition but output controversial analysis on symmetry. In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K, with focus on the two A(g) phonon modes at similar to 71.1 cm(-1) and 128.4 cm(-1). Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C-2h rather than D-3d both above and below structural phase transition. We further performed temperature-dependent Raman experiments to study the magnetism in VI3. Fano asymmetry and anomalous linewidth drop of two A(g) phonon modes at low temperatures, point to a significant spin-phonon coupling. This is also supported by the softening of 71.1-cm(-1) mode above the magnetic transition. The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3. And spin-phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.