The low energy neutral excitations of incompressible fractional quantum Hall states are called collective modes or magnetic excitons. This work shows that the interaction between the quasiparticle and quasihole forming the exciton is well described quantitatively by the unprojected composite fermion theory, except at very small wave vectors. This allows a study of large systems to determine the collective mode dispersions for general fractions up to an overall additive constant. The positions of various minima are explained by analogy to the integer quantum Hall effect.

• Received 31 July 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.1332