Brillouin scattering study of the pseudo surface acoustic mode on the (110) face of cubic crystals having elastic anisotropy ratio above unity

We report the experimental observation of a pseudosurface mode in (110)-cut cubic crystals having the anisotropy ratio η=2C44/(C 11-C12)≳1, where C11, C12, and C44 are elastic constants. The measurements have been performed with Brillouin light-scattering spectroscopy for GaAs, InSb, Ge, and InAs crystals. Results are shown for GaAs and InSb. An additional Brillouin satellite has been observed in the bulk velocity range for general propagation directions on the (110) plane; this peak is attributed to the presence of the pseudosurface mode. For all the crystals investigated, we have found that the pseudosurface mode exists for propagation directions within the range θ=±55°, where θ is the azimuthal angle measured from the [001] crystal axis. The results of calculations of the light-scattering cross section and of the propagation velocity of the pseudosurface mode are in a good agreement with the measurements.