Mobility reversal and absolute negative mobility induced by an internal degree of freedom

We study a Brownian motor that consists of two linearly coupled particles moving in a symmetric periodic potential and subjected to an unbiased harmonic driving in combination with a constant external force. Although a trajectory of the single-particle system must also be a valid trajectory of the corresponding coupled-particle system, the stability of the trajectory does not necessarily hold. It is revealed that, for proper strength of the interparticle coupling K, parametric resonance, which may break the stability of the trajectory, emerges. As a consequence, the system may fall into other attractors, regular or chaotic, and the mobility of the motor may be largely changed or even reversed. Absolute negative mobility in a much wider regime of parameter is then observed. Furthermore, the so induced absolute negative mobility is much more robust under the perturbation of external noise. This provides an effective way of tuning the collective mobility of a Brownian motor via adjusting its internal interactions only.