Incompressible states of the fractionally quantized Hall effect in the presence of impurities: A finite-size study

We have studied the effect of impurities on the incompressible states of two-dimensional electrons in a strong magnetic field by finite-size numerical calculations in the spherical geometry. For short-ranged impurity potentials the Laughlin ground state shows no screening and is found to be stable regardless of the potential strength. An analogy with acceptor and donor states of a semiconductor is drawn and ionization energies are estimated.