Collective Directional Transport in Symmetric Periodic Potentials by Breaking the Coupling Symmetry**The project supported by National Natural Science Foundation of China, the Special Funds for Major State Basic Research Projects, the Foundation for University Key Teachers by the Ministry of Education of China, Special Funds for Excellent Doctoral Dissertations, the TRAPOYT in Higher Education Institutions, and the Huo-Ying-Dong Educational Funds

Abstract

Collective unidirectional motion of an asymmetrically coupled array of oscillators in symmetric periodic potentials is studied. A directed current is observed when the drift coupling is presented, while no external biased force is applied. Negative directed current is found when varying system parameters. An addition of a periodic rocking force may enhance the efficiency of directed transport. Resonant steps of the current are found and interpreted as the mode locking between the array and the ac force. Noise-assisted transport is observed, and an optimal noise intensity can give rise to a most efficient transport. The directed transport thus can be optimized and furthermore controlled by suitably adjusting the parameters of the system.