Graphene Nanoelectromechanical Systems as Stochastic-Frequency
Oscillators
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Abstract
We measure the quality factor <i>Q</i> of electrically
driven few-layer graphene drumhead resonators, providing an experimental
demonstration that <i>Q</i> ∼ 1/<i>T</i>, where <i>T</i> is the temperature. We develop a model
that includes intermodal coupling and tensioned graphene resonators.
Because the resonators are atomically thin, out-of-plane fluctuations
are large. As a result, <i>Q</i> is mainly determined by
stochastic frequency broadening rather than frictional damping, in
analogy to nuclear magnetic resonance. This model is in good agreement
with experiment. Additionally, at larger drives the resonance line
width is enhanced by nonlinear damping, in qualitative agreement with
recent theory of damping by radiation of in-plane phonons. Parametric
amplification produced by periodic thermal expansion from the ac drive
voltage yields an anomalously large line width at the largest drives.
Our results contribute toward a general framework for understanding
the mechanisms of dissipation and spectral line broadening in atomically
thin membrane resonators