Novel travelling wave structures: few-cycle-pulse solitons and soliton molecules

We discuss a fifth order KdV (FOKdV) equation via a novel travelling wave method by introducing a background term. Results show that the background term plays an essential role in finding new abundant travelling wave structures, such as the soliton induced by negative background, the periodic travelling wave excited by the positive background, the few-cycle-pulse (FCP) solitons with and without background, the soliton molecules excited by the background. The FCP solitons are first obtained for the FOKdV equation. (paper)