Spin-orbit scattering and magnetoconductance of strongly localized electrons

The effect of a magnetic field on the tunneling probability of strongly localized electrons is calculated in the presence of spin-orbit scattering. Numerical (transfer matrix) and theoretical (replica analysis) arguments indicate a positive magnetoconductance, but no increase in the localization length. Universal and nonuniversal aspects of the tunneling probability distribution, and their relation to the symmetries of the Hamiltonian, are discussed.