Novel approach to nonlinear susceptibility in semiconductors

Abstract

We here propose a new procedure to derive a general expression of the third-order susceptibility valid for any semiconductor Hamiltonian. It relies on ourtheory for composite exciton many-body effects which is quiteappropriate to thisproblem since all optical nonlinearities in semiconductors come from exchangescatterings with the virtual excitons coupled to photons. Our expression ofχ(3) is sample volume free, as physically expected. It also contains aPauli term (exchange without Coulomb) which is missed by all bosonized excitonapproaches. This term, dominant at large detuning, is a directmanifestation of theexciton composite nature.