Quantitative Evaluation of Exciton-Exciton Interaction Energy in Bulk GaAs

The exciton-exciton(ex-ex) interaction has long been investigated from the viewpoint of excitonic nonlinear optics in a variety of semiconductors [1]. Recently, the problem has gained a renewed interest partly triggered by the progress of researches in the field of polariton Bose-Einstein condensation in a quantum well system embedded in a microcavity. In contrast to intensive theoretical studies devoted over decades, however, the quantitative evaluation of ex-ex interaction in bulk system has been lacked. Here we revisited this long-standing issue with near-infrared optical pump optical-probe/terahertz probe spectroscopy technique. In bulk GaAs at the lattice temperature 5K, we observed a blueshift of exciton absorption peak caused by the ex-ex interaction when the pump photon energy tuned to 1s-exciton resonance. Combined with the terahertz spectroscopy, the density dependence of the excitonic blueshift is evaluated, which allows to determine the ex-ex interaction strength quantitatively. The value coincides well with that predicted from mean-field theory. The dynamics of the excitonic blueshift will also be discussed with respect to the thermalization of cold exciton gas.
[1] S. Schmitt-Rink, D. S. Chemla and D. A. B. Miller, Phys. Rev. B, 32, 6601 (1985).