We investigate theoretically the non-linear dynamics of a coupled nanomechanical oscillator. Under a weak radio frequency excitation, the resonators can be parametrically tuned into a self-sustained oscillatory regime. The transfer of electrons from one contact to the other is then mechanically assisted, generating a rectified current. The direction of the rectified current is, in most unstable regions, determined by the phase shift between the mechanical oscillations and the signal. However, we locate intriguing parametrical regions of uni-directional rectified current, suggesting a practical scheme for the realization of a self-powered device in the nanoscale. In these regions, a dynamical symmetry breaking is induced by the non-linear coupling of the mechanical and electrical degrees of freedom. When operating within the Coulomb blockade limit, we locate bands of instability of enhanced gain.
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