A microscopic theory is presented which is capable of describing the influence of biexciton many-body correlations on the nonlinear optical response of the $\mathrm{Si}\left(111\right)\text{−}(2\times 1)$ surface exciton. The band structure and the quasiparticle wave functions of this surface are obtained by ab initio many-body perturbation theory within the GW method. These results are used as a basis for setting up semiconductor Bloch equations. Analyzing the optical response including many-body correlations in the coherent ${\chi }^{\left(3\right)}$ limit, it is shown that for resonant and near-resonant excitation of the surface exciton, the correlations contribute significantly to the optical response. The binding energy of the surface biexciton is predicted to be about $18\mathrm{meV}$.

• Received 13 January 2005

DOI:https://doi.org/10.1103/PhysRevB.71.235324