Surface Brillouin scattering in black phosphorus

Abstract
The surface acoustic properties of black phosphorus have been studied in the XY plane by Brillouin scattering under normal conditions. Surface acoustic phonon peaks and quasielastic scattering peaks due to the entropy mode are observed in the X direction. A quasielastic peak and a polaritonlike resonance between surface acoustic phonons and Einstein-type modes are found in the Y direction.