Degenerate Landau bands with interband disorder: A semiclassical picture

Localization in a pair of degenerate Landau levels, coupled by random interlevel matrix elements, is discussed in a semiclassical picture appropriate to the case of smooth disorder. It is shown that there are two distinct energies on either side of the band center where delocalization occurs. Each transition belongs to the same universality class as that of a nondegenerate Landau level in a random potential. Using a simple physical picture for the eigenstates, I will further argue that, unique to this model, the localization length also diverges at the band center, in accordance with recent results of Hikami, Shirai, and Wegner for white-noise disorder [Nucl. Phys. B 408, 415 (1993)].