Biexciton Dispersion in the Degenerate-Band Case: CuBr as an Example

In CuBr, biexcitons are excited resonantly by the absorption of two photons which are provided by two different laser sources. By a change in the geometrical configuration of the experiment, the wave vector →K of these biexcitons can be tuned. Thus, for the first time, a momentum spectroscopy of biexciton states is achieved. The biexciton dispersion E(→K) is established and a splitting of biexciton states, degenerate at →K=0, is observed. This dispersion is fully explained by the band parameters known from the exciton case.