Biased Motion in a Symmetric Periodic Potential by Breaking Temporal Symmetry**The project supported by National Natural Science Foundation of China, the Special Funds for Major State Basic Research Projects, and the Foundation for University Key Teachers by the Ministry of Education of China

Abstract

Unidirectional transport of a particle in a spatially periodic and symmetric potential under a periodic force with broken temporal symmetry is studied. With a collaboration of the potential field and the asymmetric ac force, a dc current can be observed. Resonant current steps are found for a finite period of the ac force. A phase diagram of these resonant steps is given. Stochastic-resonance-like directional transport induced by thermal noises is revealed.