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We present a generalization of the composite Fermion picture for a muticomponent quantum Hall plasma which contains particle with different effective charges. The model predicts very well the low-lying states of a $��=5/2$ quantum Hall state found in numerical diagonalization., 5 pages, 3 figures

Spin polarization of the "second generation" nu_e=4/11 fractional quantum Hall state (corresponding to an incompressible liquid in a one-third-filled composite fermion Landau level) is studied by exact diagonalization. Spin phase diagram is determined for GaAs structures of different width and electron concentration. Transition between the polarized and partially unpolarized states with distinct composite fermion correlations is predicted for realistic parameters., Comment: 5 pages, 3 figures

If the Zeeman energy is small, the lowest energy excitations of a two dimensional electron gas at filling factor nu=1 are spin waves (spin flip excitations). At nu slightly larger (smaller) than unity, reversed spin electrons (spin holes) can form bound states with K spin waves that are known as skyrmions, S_K^- (antiskyrmions, S_K^+). It is suggested in this work that a valence hole can also bind K spin waves to form an excitonic complex X_K^+, analogous to the S_K^+. One spin hole of the S_K^+ is simply replaced by the valence hole. At nu=1, the (S_K^-)-(X_K^+) attraction can potentially lead to different behavior., 9 pages, 4 figures, invited lecture at SID8, Buffalo (2002)

A theory of charged excitons X- in a dilute 2D electron gas in a high magnetic field is presented. In contrast to previous calculations, three bound X- states (one singlet and two triplets) are found in a narrow and symmetric GaAs quantum well. The singlet and a "bright" triplet are the two optically active states observed in experiments. The bright triplet has the binding energy of about 1 meV, smaller than the singlet and a "dark" triplet. The interaction of bound X-'s with a dilute 2D electron gas is investigated using exact diagonalization techniques. It is found that the short-range character of the e:X- interactions effectively isolates bound X- states from a dilute e-h plasma. This results in the insensitivity of the photoluminescence spectrum to the filling factor nu, and an exponential decrease of the oscillator strength of the dark triplet X- as a function of 1/nu$., Comment: 8 pages, 5 figures, submitted to Phys.Rev.B

Two-dimensional systems containing Ne electrons and Nh holes (Ne>Nh) strongly correlated through Coulomb interactions in the presence of a large magnetic field are studied by exact numerical diagonalization. Low lying states are found to contain neutral (X0) and negatively charged (X-) excitons and higher charged exciton complexes (Xk-, a bound state of k neutral excitons and an electron). Representing these states in terms of angular momenta and binding energies of the different exciton complexes, and the pseudopotentials describing their interactions with electrons and with one another, permits numerical studies of systems that are too large to investigate in terms of individual electrons and holes. Laughlin incompressible ground states of such a multi-component plasma are found. A generalized composite Fermion picture based on Laughlin type correlations is proposed. It is shown to correctly predict the lowest band of angular momentum multiplets for different charge configurations of the system for any value of the magnetic field., 7 pages, 4 figures (RevTeX+epsf); talk at NATO ARW

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, RevTeX + 4 EPS figures formatted with epsf.sty; submitted to Phys. Rev. Lett