We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttles. The oscillation frequencies of two shuttles are mode locked to integer multiples of the applied voltage frequency $\omega$. We show that left-right-symmetric double shuttles may generate direct net current due to bistable motions caused by parametric instability. The symmetry-broken direct current appears near $\omega ={\Omega }_0/(2j-1)$, ($j=1,2,\dots$), where ${\Omega }_0$ is the dressed resonance frequency of the relative motion of the two shuttles.

• Received 16 August 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.216804