Localization in nonchiral network models for two-dimensional disordered wave mechanical systems

Scattering theoretical network models for coherent wave mechanical systems with quenched disorder are investigated. We focus on universality classes f or nonchiral two-dimensional systems. The phase diagram in the parameter sp ace of scattering strengths is determined. Models breaking time reversal sy mmetry contain only one attractive fixed point, that of strong localization . For spin-1/2 systems with time reversal symmetric spin scattering localiz ation-delocalization transitions occur. Multifractal exponents and quasi-on e-dimensional localization lengths are calculated numerically and found to be related by conformal invariance. [S0031-9007(98)08127-7].