Divergences of the localization lengths in the two- dimensional, off-diagonal Anderson model on bipartite lattices

We investigate the scaling properties of the two-dimensional (2D) Anderson model of localization with purely off-diagonal disorder (random hopping). Using the transfer-matrix method and finite-size scaling we compute the infinite-size localization lengths for bipartite square and hexagonal 2D lattices, non-bipartite triangular lattices and different distribution functions for the hopping elements. We show that for small energies the localization lengths in the bipartite case diverge with a power-law behavior. The corresponding exponents are in the range $0.2 - 0.6$ and seem to depend on the type and the strength of disorder.