Dynamics and statistical mechanics of a diatomic φ4 chain

We examine the dynamics and the statistical mechanics of a nonlinear diatomic model for a solid which may undergo a displacive structural phase transition. In addition to the familiar linear (phonon) oscillations, nonlinear (kink soliton) vibrations are found which behave as elementary excitations of the system. The nonlinear kinks give rise to a central peak in the dynamical structure factor. The analytic results obtained are supported by constant temperature molecular dynamics simulations of the lattice.