Propagation of acoustic and optical solitons in nonlinear diatomic chains

The authors present an analytic and numerical study of a nonlinear diatomic chain with a quartic interaction potential between nearest neighbours. In the continuum approximation using scaling arguments and a decoupling ansatz for the motion of the two different masses they find 'acoustic' pulse type excitations which obey a modified Boussinesq equation and 'optical' envelope type solitary solutions of a nonlinear Schrodinger equation. Computer simulations on their propagation and interaction show these excitations to be long lived.