COMPARATIVE-STUDY OF NONLINEAR LOCALIZED MODES OF DIATOMIC CHAINS WITH 2 TYPES OF QUARTIC NONLINEARITY

We study the model on a one-dimensional diatomic chain with two types of nonlinearity, i.e., quartic nearest-neighbor interparticle interact ion and quartic substrate potential, respectively, and obtain analytic al expressions for nonlinear localized modes with frequencies within a nd above the gap of the linear spectrum. The difference between the so lutions for the two types of nonlinearity is found, and this differenc e almost disappears when the mass of the heavy atoms is three times gr eater than that of the light ones. This similarity of interparticle in teraction nonlinearity to substrate nonlinearity is in agreement with the origin of the nonlinear substrate potential.