SURFACE-STATE-INDUCED 2ND-HARMONIC GENERATION

We propose a simple and intuitively clear method for analysing the sec ond-harmonic generation induced by surface states. The two-band model is used to calculate the wave functions and Green's function so that t he second-harmonic current density and polarization can be evaluated. Assuming that the polarization is concentrated on the surface, we calc ulated the reflection intensity of the second-harmonic light. We apply our formalism to the L-gap surface states on the silver (110) surface and obtain results that agree reasonably well with experiments.