Microscopic description of a quantum Hall transition without landau levels.

By restricting the motion of a high-mobility 2D electron gas to a network of channels with smooth confinement, we were able to trace, both classically and quantum mechanically, the interplay of backscattering, and of the bending action of a weak magnetic field. Backscattering limits the mobility, while bending initiates quantization of the Hall conductivity. We demonstrate that, in restricted geometry, electron motion reduces to two Chalker-Coddington networks, with opposite directions of propagation along the links, which are weakly coupled by disorder. The interplay of backscattering and bending results in the quantum Hall transition in a nonquantizing magnetic field, which decreases with increasing mobility. This is in accord with the scenario of floating up delocalized states.