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We study the Langevin dynamics of a two-dimensional discrete oscillator chainabsorbed on a periodic substrate and subjected to an external localized pointforce. Going beyond the commonly used harmonic bead-spring model, we consider anonlinear Morse interaction between the next-nearest-neighbors. We focusinterest on the activation of directed motion instigated by thermalfluctuations and the localized point force. In this context the localtransition states are identified and the corresponding activation energies arecalculated. As a novel feature it is found that the transport of the chain inpoint force direction is determined by stepwise escapes of a single unit orsegments of the chain due to the existence of multiple locally stableattractors. The non-vanishing net current of the chain is quantitativelyassessed by the value of the mobility of the center of mass. It turns out thatthe latter as a function of the ratio of the competing length scales of thesystem, that is the period of the substrate potential and the equilibriumdistance between two chain units, shows a resonance behavior. More preciselythere exist a set of optimal parameter values maximizing the mobility.Interestingly, the phenomenon of negative resistance is found, i.e. themobility possesses a minimum at a finite value of the strength of the thermalfluctuations for a given overcritical external driving force.

Resonance-like phenomena of the mobility of a chain of nonlinear coupled oscillators in a two-dimensional periodic potential