If time permits, I will briefly address the possibility to generate an acoustic frequency comb by self-induced parametric coupling. The frequency comb arises as the result of the formation of a limit cycle (LC) following a Hopf bifurcation. We employ a novel pump-noisy-probe technique to record which mechanical excitation sidebands merge at the bifurcation. By thorough theoretical modelling we reveal the mechanism for this comb generation and show that it does not result from locking or synchronizing pre-existing frequencies. Instead, the comb frequency arises from the nonlinear properties of the system and can continuously be tuned by the drive power.
Greifswald Physics Colloquium: Elke Scheer (Konstanz)
Physikalisches Kolloquium
In collaboration with: M. Fu, F. Yang, B. Bosnjak, Z. Shi, O. Ameye, J. Kosata, J. del Pino, Y. Juang, O. Zilberberg, R. H. Blick
Controlling the properties of mechanical devices over a large range is interesting for many applications such as filters and sensors as well as for fundamental research such as nonlinear dynamics, optomechanics and quantum readout.
Here I will report on a novel on-chip tunable structure composed of a suspended siliconnitride (SiN) membrane with a graphene layer on top which is connected to metal electrodes. Taking advantage of the high electrical and thermal conductivity of graphene and the difference in the thermal expansion coefficients of SiN and the metal, we developed a device in which the graphene-gold interface acts to heat the suspended membrane locally, by injecting a dc current through the graphene. With this device we realize an extreme large eigenfrequency tuning of the vibration mode and the breaking of the symmetry of the membrane. An analytical model taking into account the thermal expansion coefficients and contact resistances of the components quantitatively describes the threshold loading power needed to induce spatial deflection and the curvature of the spatial deflection. This device may act as proof-of-principle for a compact on-chip excitation scheme for multidimensional and composite nanomechanical resonators.