Inhomogeneous soliton ratchets under two ac forces

Abstract

We extend our previous work on soliton ratchet devices ͓L. Morales-Molina et al., Eur. Phys. J. B 37, 79 ͑2004͔͒ to consider the joint effect of two ac forces including nonharmonic drivings, as proposed for particle ratchets by Savele'v et al. ͓Europhys. Lett. 67, 179 ͑2004͒; Phys. Rev. E 70, 066109 ͑2004͔͒. Current reversals due to the interplay between the phases, frequencies, and amplitudes of the harmonics are obtained. An analysis of the effect of the damping coefficient on the dynamics is presented. We show that solitons give rise to nontrivial differences in the phenomenology reported for particle systems that arise from their extended character. A comparison with soliton ratchets in homogeneous systems with biharmonic forces is also presented. This ratchet device may be an ideal candidate for Josephson junction ratchets with intrinsic large damping. The understanding of ratchet mechanisms is a very active field of wide interest by its potential application in the design of devices with new transport properties. The key feature of ratchet devices is their ability to rectify the motion of particles subjected to an external ac force with zero time average. Originally proposed as a toy model for molecular motors, in the last decade many proposals have been put forward for devices that use this ratchet phenomenon in different applications ͓1͔. Ratchets working with extended particles ͑solitons͒ were subsequently studied as a generalization of particle ratchets ͓2͔. Recently, an overdamped ratchet device for a single particle driven by two ac forces was introduced by Savele'v and coworkers ͓3͔, in which the combination of the two drivings produced a variety of interesting phenomena and allowed a finely tunable control. In view of the rich behavior demonstrated by this system, a very natural issue is its extension to soliton ratchets that have important applications which can benefit from this proposal.Soliton ratchets under the presence of two ac forces have been extensively studied ͓4,5͔ in homogeneous systems, i.e., without an underlying ratchet potential. In this case, it has been shown that the ratchet mechanism works only for asymmetric biharmonic forces, where the appearance of a directed translational motion is a result of the effective coupling between the internal mode ͑oscillations of the soliton width͒ and the external driving force. In this paper, we focus on a soliton ratchet device recently studied by us ͓7,8͔, based on a nonlinear Klein-Gordon model with a lattice of deltalike inhomogeneities that induce a ratchet potential for the solitons. As we will see, one of the advantages of our model as compared to the homogeneous system is that it works irrespectively of the symmetry of the ac driving: Directional transport takes place for ac forces with commensurate frequencies. Moreover, in the homogeneous system the motion drastically decreases for increasing damping, due to the slowing down of the soliton width oscillations ͓5͔, while in the present system the ratchet phenomenon is present up to rat...

Creation and Annihilation of Fluxons in ac-driven Semiannular Josephson Junction

“…Complex switching distributions has been obtained for ac-driven annular JJs and theoretical explanation has been provided for the multipeaked experimental observations [17]. The behavior of fluxon under two ac forces has been studied and it was shown that the direction of motion of fluxon is dependent on ratio of frequencies, amplitudes and phases of the harmonic forces [18]. In this work, we study the effect of an ac-bias applied in the plane of a semi-annular Josephson junction.…”

Kink ratchets in the Klein-Gordon lattice free of the Peierls-Nabarro potential

“…Unlike point-like particles, solitons can have internal vibrational modes [20] and these modes can strongly affect the ratchet dynamics especially for underdamped case [21,22]. So far, ratchet dynamics have been studied for a number of continuum soliton bearing systems [19,21,22,23,24,25,26,27,28], while in many applications ratchet was observed for discrete kinks [13,14,15,16]. Effects of discreteness on kink ratchets have been studied by Zolotaryuk and Salerno [29].…”