Low-energy vibrations at the InSb(110) surface

We present a study of low-energy vibrations at the InSb(110) surface along the {Γ}Y{} direction. Surface phonons have been measured by He inelastic scattering and a theoretical analysis has been performed by means of first-principles calculations. We have been able to distinguish the surface acoustic mode above the Rayleigh wave and to identify a surface resonance and an optical surface mode at higher energy. Theoretical calculations are shown to be in agreement with the detected phonon dispersion curves except for the surface resonance which is found 1 meV higher than calculated.