EFFECTS OF OFF-DIAGONAL NONLINEARITY ON THE TIME EVOLUTION OF AN INITIALLY LOCALIZED MODE

A modified one-dimensional nonlinear Schrodinger equation which includ es off-diagonal nonlinearity is proposed to describe the behavior of e lectrons via electron-phonon couplings in the Su-Schrieffer-Heeger Ham iltonian. We find an interesting self-trapping phenomenon of electrons which takes place when the magnitude of the nonlinearity parameter is close to the value of the hopping integral. For a periodic lattice, t he ballistic propagation of a wave packet is found in this modified on e-dimensional nonlinear Schrodinger equation, and the propagation rate increases with the increase of nonlinearity parameter except in the s elf-trapping interval. When diagonal disorder is introduced, the elect ronic states are localized, and no delocalization effect of the off-di agonal nonlinearity is found. These results are quite different from t hat in the diagonal nonlinear lattice, where delocalization is found.