Supersonic vibron solitons and their possible existence in polypeptides.

Nonlinear interactions of vibrons with lattice solitons due to the soft cubic nonlinearity in a quasi-one-dimensional lattice yield supersonic vibron solitons. Their binding energy is larger than those of the conventional Davydov solitons and vibron solitons, and their propagation velocity is uniquely determined in contrast to the latter two. Examination of parameters in the model Hamiltonian for polypeptides leads to the result that the supersonic vibron solitons obtained here are more likely to be realizable than the Davydov solitons and the conventional vibron solitons in alpha-helical proteins.