Exact exponents for the spin quantum Hall transition

Sire consider the spin quantum Wall transition which may occur in disordere d superconductors with unbroken SU(2) spin-rotation symmetry but broken tim e-reversal symmetry. Using supersymmetry, we map a model for this transitio n onto the two-dimensional percolation problem. The anisotropic limit is an sl(2 \ 1) supersymmetric spin chain. The mapping gives exact values for cr itical exponents associated with disorder averages of several observables i n good agreement with recent numerical results. [S0031-9007(99)09270-4].