High-Q MEMS resonator as a probe of superfluid 4He in the ballistic regime
LTL Quantum Physics Seminar (Nanotalo). Speaker: T. Kamppinen (Rota).
Immersed oscillating objects have proven to be useful and multifunctional probes in studies of superfluid 4He and 3He. Smaller devices are required for higher sensitivity. Thus, we have fabricated suspended aluminium MEMS resonators, which are operated at frequencies from 300 kHz to 500 kHz. The motion of these devices is actuated and detected with a magnetomotive method. Q-values up to 20 000 and force resolution ~4 fN have been achieved.
We have measured response of these devices at temperatures from 15 mK to 1 K in vacuum and superfluid 4He. The temperature dependent intrinsic (vacuum) width and ballistic phonon and roton drag (4He II) enables thermometry with these devices at milliKelvin/sub-Kelvin temperatures. At large oscillation amplitudes, the response becomes nonlinear and shows Duffing-like behaviour. Emission of vortex rings and possibility to study single vortices with such devices are also discussed.