ON THE ORIGIN OF THE SURFACE ANISOTROPY IN OPTICAL 2ND-HARMONIC GENERATION FROM STEPPED AL(001) SURFACES

A microscopic calculation of the anisotropic nonlinear optical surface response of vicinal Al(001) is performed within a two-band model. As previously found for flat Al(111), the tangential surface current exhi bits a surprisingly large penetration depth. This large penetration de pth, however, does not necessarily imply a weak sensitivity of the ani sotropic response to surface conditions. The anisotropy resulting from the nonsymmetric stacking of the lattice planes parallel to the macro scopic surface is very much larger than the anisotropy due to the nons ymmetric density corrugation at stepped jellium surfaces.