Dissipation and feedback cooling of graphene and MoS$_{2}$ nanomechanical resonators

The interesting mechanical and electronic properties of 2-dimensional materials make them candidates for nano-electromechanical systems. Remarkably, the mechanical resonance linewidth of such suspended structures is found to be invariably low at room temperature. Time-domain measurements were used as a tool to differentiate between dissipation and non-dissipative frequency fluctuations, thus providing more insight in the origin of the low linewidth. We perform time-domain measurements on MoS$_{2}$ resonators with thickness down to a single layer, and compare the relaxation times obtained from ringdown measurements to the resonance linewidth obtained from Brownian motion and driven frequency responses. We conclude that dephasing plays a negligible role at room temperature, and that the spectral line-width is bounded by dissipation. To modify the damping we introduce an optical feedback technique. We demonstrate continuous tuning of the oscillator linewidth, by modifying the linewidth over 2 orders of magnitude. Feedback also enables cooling of the fundamental mode of graphene and MoS$_{2}$ drum resonators down to an effective temperature of 100 K.