Observation of exciton-energy renormalization by the biexciton gas in semiconductors

Energy renormalization of the excitonic resonance due to pair correlations within the electron gas in semi-conductors is well known. Higher order correlations give rise to quasiparticles such as biexcitons, yet the energy renormalizations associated with a given density of these complexes are unknown. We present ultrafast polarization-selective pump-continuum-probe data which demonstrate that, at high density, interband recombination in wide-gap semiconductors at 4 K is preceded by a phase dominated by biexcitons and that there is a distinct blue-shift of the exciton resonance due to the biexciton gas.