A single model is presented which represents both of the two apparently unrelated localization problems of the title. The phase diagram of this model is examined using scaling ideas and numerical simulations. It is argued that the localization length in a spin-degenerate Landau level diverges at two distinct energies, with the same critical behavior as in a spin-split Landau level, and that all states of a charged particle moving in two dimensions, in a random magnetic field with zero average, are localized.

• Received 27 September 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.1510