Incompressible states of negatively charged magneto-excitons

We study the system of up to four negatively charged magneto-excitons (X-'s) in the spherical geometry, using the exact-diagonalization techniques. At low energies, X-'s are bound and behave like charged particles without internal dynamics. The pseudopotential describing X-:X- scattering is almost identical to that of electrons and the low-lying few X- states correspond to the few-electron states. The total angular momentum of the ground state depends on the effective filling factor nu and vanishes at its special values. The analogs to the Laughlin nu=1/3 state and the Jain nu=2/5 state of electrons are found. The X- system is predicted to exhibit the fractional quantum Hall effect.