LINEAR AND NONLINEAR-OPTICAL CHARACTERISTICS OF THE FALICOV-KIMBALL MODEL

We calculate the linear and nonlinear optical properties of the Falico v-Kimball model for a mixed-valent system within the self-consistent m ean-field approximation. Second-harmonic generation can only occur if the mixed-valent state has a built-in coherence between the itinerant d electrons and the localized f holes. By contrast, second-harmonic ge neration cannot occur for solutions of the model with f-site occupatio n as a good quantum number. As an experimental test of coherence in mi xed-valent compounds we propose a measurement of the dynamic second-or der susceptibility.