LOCALIZATION TRANSITION IN QUANTUM PERCOLATION

Connecting perfect one-dimensional leads to sites i and j on the quant um percolation (QP) model, we calculate the transmission coefficient T -ij(E) at an energy E near the band center and the averages of Sigma(i j)T(ij), Sigma(ij)r(ij)(2)T(ij) and Sigma(ij)r(ij)(4)T(ij) to 10th ord er in the concentration p. All three series diverge at a finite thresh old p(q), with exponents gamma, gamma + 2 nu and gamma + 4 nu. We find nu = 0.38 +/- 0.007i and 0.50 +/- 0.05 in 3 and 2 dimensions, differi ng from ''usual'' Anderson localization and violating the bound nu gre ater than or equal to 2/d of Chayes et al. Thus, QP belongs to a new u niversality class.