Two-roton bound state in the fractional quantum Hall effect

Although a number of studies focused on the excitations at Landau level filling v = 1/3, it is not yet clear whether the lowest-energy excitation at long wavelengths is described correctly by the single model approximation (SMA) or was instead a two-roton excitation. This article provides evidence indicating that at v = 1/3, the lowest-energy excitation in the long-wavelength limit is not a single exciton but rather a two-photon mode.