BIPOLARITON IN QUANTUM-WELLS

We develop the bipolariton concept for a quasi-2D excitonic molecule ( m) in quantum wells (QWLs). The bipolariton wave equation, which inclu des both the exciton-exciton (x-x) attraction and the x-photon (gamma) coupling, is analysed. In the 2D bipolariton model, a quasi-2D m exis ts in QWLs mainly as two quasi-bound surface polaritons and, consequen tly, decays mainly into two outgoing surface polaritons. In quasi-2D G aAs QWLs the polariton renormalizations give rise to a ''Mexican hat'' structure in the m dispersion at small momenta together with a consid erable increase of both the m effective binding energy epsilon(m) and the inverse m radiative lifetime Gamma(m). A van Hove singularity in t he joint density of polariton states is responsible for this effect.