Underlying mechanisms of the self-sustained oscillation of a nanomechanical stochastic resonator in a liquid

We study the stochastic response of a nanomechanical resonator in a liquid connected to a feedback loop to increase the quality $(Q)$ factor. We distinguish two regimes in the oscillation. Below a critical value of the feedback gain, an effective increase of the Q factor and temperature is produced. When the gain surpasses the critical value, the resonator initially behaves as having negative damping until the saturation of the system comes into play and a steady situation is reached. In this regime, frequency stabilities of about 1 part per 10⁶ can be achieved.