Energy Flow Puzzle of Soliton Ratchets

TL;DR

This paper investigates how directed energy transport occurs in soliton ratchets, revealing that energy flow is driven by inhomogeneous energy exchange mediated by internal kink modes, despite zero total field momentum.

Contribution

It uncovers the mechanism of energy flow in soliton ratchets, emphasizing the role of inhomogeneous energy exchange and internal kink modes, and discusses effects of discretization and combined drivings.

Findings

Energy flow is due to inhomogeneous exchange with external driving.

Internal kink modes are essential for energy transport.

Discretization and combined ac/dc drivings influence the process.

Abstract

We study the mechanism of directed energy transport for soliton ratchets. The energy flow appears due to the progressive motion of a soliton (kink) which is an energy carrier. However, the energy current formed by internal system deformations (the total field momentum) is zero. We solve the underlying puzzle by showing that the energy flow is realized via an {\it inhomogeneous} energy exchange between the system and the external ac driving. Internal kink modes are unambiguously shown to be crucial for that transport process to take place. We also discuss effects of spatial discretization and combination of ac and dc external drivings.