Doublet structure of emission spectra from fractional quantum Hall states

A suppression of the exciton dispersion by an incompressible quantum liquid strongly affects the recombination emission spectrum. It comprises two parts; one of them originates from a direct recombination of k=0 excitons, and the other from indirect, single magnetoroton, transitions from an extensive area in k space, kl~=1, l is the magnetic length. Intensities of the peaks show opposite temperature dependencies. We show that the minimal frequency of magnetorotons may be found from emission spectra by a proper treatment of experimental data.