Dephasing of three- and two-dimensional magnetoexcitons in InxGa1−xAs

We investigate the dephasing of three- and two-dimensional magnetoexcitons in InxGa1−xAs at low temperatures by femtosecond four-wave mixing. In both cases the dephasing time T2 increases substantially with magnetic field. For a cyclotron energy one order of magnitude larger than the three-dimensional exciton binding energy, T2 rises by a factor of about 4. This is interpreted in terms of a considerably reduced scattering cross section of the 1s magnetoexciton due to the magnetic confinement.