MANY-ELECTRON EFFECTS ON DONOR STATES IN A 2-DIMENSIONAL ELECTRON-GAS IN A STRONG MAGNETIC-FIELD

The many-electron effects on donor-bound intra- and inter-Landau-level excitation spectrum in a two-dimensional electron gas in a strong magnetic field are investigated. At nu = 2 the donor related far infrared (FIR) spectrum shows a blueshift and an additional structure below cyclotron energy. At nu = 1 the spin polarized ground state is unstable against the formation of donor-bound intra-Landau-level spin flip excitations (spin waves). The FIR spectrum of this new ground state is calculated and shown to be distinct from either the paramagnetic (nu = 2) or the ferromagnetic (nu = 1 ) ground states. These findings provide a qualitative understanding of recent experiments by Cheng et al.