Stabilization of ratchet dynamics by weak periodic signals

We study the influence of weak periodic signals on the transport properties of underdamped ratchets. We find that the constant current intervals related to the ratchet can be significantly enlarged by a weak subharmonic signal that is in phase with the internal driver. This stabilization phenomenon is found to exist both in absence and in presence of noise. The dependence of this effect on the phase of the applied signal is also investigated.