We report a numerical investigation of localization in the SU(2) model
without diagonal disorder. At the band center, chiral symmetry plays an
important role. Our results indicate that states at the band center are
critical. States away from the band center but not too close to the edge of the
spectrum are metallic as expected for Hamiltonians with symplectic symmetry.Comment: accepted in Proceedings of Localisation 2002 Conference, Tokyo, Japan
(to be published as supplement of J. Phys. Soc. Japan