Propagation of solitons in hydrogen-bonded chains with mass variation

In the context of the soliton mechanism for proton transport in hydrogen-bonded networks we analyze properties of kink propagation through disordered hydrogen-bonded chain when realistic mass variation along the chain is created through deuterium substitutions. We provide an interpretation for the kink propagation in the chain as the motion of a particle with variable mass. We show that mass impurity localized modes are excited only above a certain threshold of kink velocity and, as a result, the presence of mass impurities renormalizes the maximal kink velocity in the medium. The existence of a critical kink velocity for the excitation of impurity mode appears also in the study of the interaction of kink with a single impurity.