Excitonic Ions and Pseudopotentials in 2D Systems: Evidence for Quantum   Hall States of an X- Gas
  Systems of up to twelve electrons and six holes on the Haldane sphere are studied by exact numerical diagonalization. The low lying states of the system involve bound excitonic complexes such as (X^n)-. The angular momenta of these complexes and the pseudopotentials describing their interaction are determined. The similarity to the electron pseudopotential suggests the possibility of incompressible ground states of a gas of X- ions for nu<=1/3. The nu=1/3 state of three X-'s is found. 
Arkadiusz Wojs, Pawel Hawrylak, and John J. Quinn