Quasi-Spin-Charge Separation and the Spin Quantum Hall Effect

We use quantum field theory methods to study the network model for the spin quantum hall transition. When the couplings are fine tuned in a certain way, the spin and charge degrees of freedom, corresponding to the supercurrent algebras su(2) and osp(2|2) respectively, decouple in the renormalization group flow. The infrared fixed point of this simpler theory is the coset osp(4|4)/su(2) which is closely related to the current algebra osp(2|2) but not identical. Some critical exponents are computed and shown to agree with the recent predictions based on percolation.