SURFACE ANISOTROPY IN OPTICAL 2ND-HARMONIC GENERATION .2. EMBEDDING APPROACH TO AL(111) AND VICINAL AL(001) SURFACES

The anisotropic nonlinear optical response of Al(111) and vicinal Al(001) surfaces is calculated microscopically with the aim of analyzing second harmonic generation measurements on these systems. The electronic states and currents are evaluated within the embedding approach which provides a more accurate description than the two-band model for Al slabs used previously by Petukhov and Liebsch. Although we find appreciable differences in detail, the qualitative picture derived from these calculations is confirmed. In particular, we verify that the anisotropic current giving rise to the chi(xxx)(omega) component of the nonlinear surface polarizability exhibits a remarkably large penetration depth and a strong frequency dependence close to the main interband transitions of Al. For Al(111) as well as vicinal Al surfaces, the physical origin of the anisotropy is the nonsymmetric stacking of the lattice planes parallel to the macroscopic surface rather than the corrugation of the outer electronic density profile.