Dimer motion on a periodic substrate: Spontaneous symmetry breaking and absolute negative mobility

TL;DR

This paper investigates how two coupled particles on a symmetric periodic substrate can exhibit spontaneous directed motion and negative mobility due to non-convex interactions, even under symmetric conditions and external driving.

Contribution

It reveals that non-convex interactions enable spontaneous symmetry breaking and negative mobility in overdamped coupled particles on a periodic substrate.

Findings

Spontaneous directed motion occurs with appropriate external driving.

Thermal noise induces fast diffusion and restores ergodicity.

Dimer exhibits negative mobility under static bias force.

Abstract

We consider two coupled particles moving along a periodic substrate potential with negligible inertia effects (overdamped limit). Even when the particles are identical and the substrate spatially symmetric, a sinusoidal external driving of appropriate amplitude and frequency may lead to spontaneous symmetry breaking in the form of a permanent directed motion of the dimer. Thermal noise restores ergodicity and thus zero net velocity, but entails arbitrarily fast diffusion of the dimer for sufficiently weak noise. Moreover, upon application of a static bias force, the dimer exhibits a motion opposite to that force (absolute negative mobility). The key requirement for all these effects is a non-convex interaction potential of the two particles.