Efficiency optimization in forced ratchets due to thermal fluctuations

The average current and efficiency of an overdamped Brownian particle, moving in an asymmetric potential and subject to an external driving force is studied by Langevin equation simulations. We found that there is a regime where the efficiency can be optimized at finite temperatures, contradicting the earlier findings (H. Kamegawa et al. Phys. Rev. Lett. 80 (1998) 5251). This, in fact, proves that thermal fluctuations contribute to the efficiency of the forced thermal ratchets. The conditions for achieving maximum flux and efficiency are different as claimed in previous investigations. We also discuss the influence of these quantities on the period of the external driving force. We argue that the theoretical results are valid only in the limiting case where the period of the external driving force is infinity.