External-field-induced electric dipole moment of biexcitons in a semiconductor

We report on the observation of an electric-field-induced electric dipole moment of biexcitonic molecules in a GaAs/${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As superlattice. The macroscopic oscillating electric field, associated with the microscopic vibronic wave-packet dipole moments, is monitored by time-resolved transmittive electro-optic sampling. The field dependence of the biexcitonic binding energy is detected by transient four-wave mixing. From this experiment, an ultrafast nonresonant excitation mechanism of biexcitons is inferred.