CHIRAL METAL AS A FERROMAGNETIC SUPER SPIN CHAIN

The electrons on the surface of a disordered multi-layer integer quant um Hall system constitute an unusual chiral metal with ballistic motio n transverse to the field, and diffusive motion parallel to it. We pre sent a non-perturbative analytic treatment of an appropriate model, co nsisting of disordered chiral fermions in two dimensions. A supersymme tric generating functional is set up for the correlation functions of this system. The strong disorder limit is mapped into a supersymmetric spin chain, with ferromagnetic exchange coupling, reflecting the elec tron's chiral motion. The ferromagnetic ground state and the spin wave excitations, corresponding to the diffusion modes of the chiral metal , are found exactly. The parametric density of states correlator in th e ergodic limit is computed from a Boltzmann-weighted sum over low-ene rgy spin states. The result is of a universal form and coincides with that for a hermitian random matrix.