Chiral metal as a Heisenberg ferromagnet

The two-dimensional surface of an integer quantum hall multilayer is mapped onto a Heisenberg spin chain with ferromagnetic coupling. Using this mapping it is shown nonperturbatively that the surface states constitute a very anisotropic metal in the infinite size limit. For multilayers of finite size, two diffusive mesoscopic regimes are identified and the conductance fluctuations are calculated perturbatively for both. The Heisenberg spin-chain representation is used to study the directed wave problem and the exact result is obtained that the mean-square deflection of a directed wave grows as the square root of the propagation distance.