Raman Tensor of Layered Black Phosphorous

Black phosphorous is an orthorhombic with a strong Raman anisotropy in the basal and cross plane. However, up to now, almost all the studies on anisotropy of black phosphorous have focused on basal plane but neglected cross plane. Here, we performed a systematic angle-resolved polarized Raman scattering on the basal and cross plane of black phosphorous and obtained its integral Raman tensors. In addition, we discovered that Raman intensity ratio ( I xx :I yy :I zz ) of A_1^g mode is 256:1:5 when the polarization direction of incident light is along different crystal axes. According to first-principle calculated results, we confirmed that the strong Raman anisotropy is due to larger differential polarizability of A_1^g mode along a-axis. This phenomenon is also observed in the A_2^g mode.