Observation of Multiple Magnetorotons in the Fractional Quantum Hall Effect
19 March 2001
Magnetorotons in the dispersions of collective gap modes of fractional quantum Hall liquids are determined in resonant inelastic scattering experiments. Two deep magnetoroton minima are observed at nu = 2/5, while a single deep minimum is resolved at nu = 1/3. The observations are the first evidence of multiple roton minima in gap excitations of the FQH liquid. The results are consistent with Chern-Simons and composite fermion evaluations that predict multiple roton minima for states with nu > 1/3.