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 inte rnal dynamics. The pseudopotential describing X--X- scattering is almost id entical 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 (CS ) depends on the effective filling factor nu and vanishes at its special va lues. The analogs to the Laughlin nu = 1/3 state and the Jain nu = 2/5 stat e of electrons are found. The X- system is predicted to exhibit the fractio nal quantum Hall effect (FQHE). (C) 1998 Elsevier Science B.V. All rights r eserved.