Onset of spatiotemporal chaos in damped anharmonically driven sine-Gordon systems

The onset is demonstrated of spatiotemporal chaos arising from the competition between sine-Gordon-breather and kink-antikink-pair solitons by reshaping of a sinusoidal force. After introducing soliton collective coordinates, Melnikov's method is applied to the resulting effective equation of motion to deduce the parameter-space regions of the ac force where chaotic instabilities are induced. The analysis reveals that the chaotic threshold amplitude when altering solely the pulse shape presents a minimum when the transmitted impulse is maximal, the remaining parameters being held constant. The universality of the results is shown by studying the behaviour of the Lyapunov exponent from a simple recursion relation which models an unstable limit cycle. Computer simulations of the sine-Gordon system show good agreement with the theoretical predictions. Additionally, it is found that the reshaping-induced order ↔ chaos route is especially rich, including transitions from a two-breather state to a spatially uniform, periodic oscillatory state. The appearance of this spatially uniform state is explained by means of geometrical resonance analysis.