  Two elastically coupled nanomechanical resonators driven independently near
their resonance frequencies show intricate nonlinear dynamics. The dynamics
provide a scheme for realizing a nanomechanical system with tunable frequency
and nonlinear properties. For large vibration amplitudes the system develops
spontaneous oscillations of amplitude modulation that also show period doubling
transitions and chaos. The complex nonlinear dynamics are quantitatively
predicted by a simple theoretical model.
