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Driving a nanomechanical resonator with phonon wind in superfluid 4He

Speaker: Sergey Kafanov (Lancaster)
Date: Wednesday 10 October 2018
Time: 15:00
Venue: Queens Buildings N/3.28

Microelectromechanical (MEMS) and nanoelectromechanical systems (NEMS) are ideal candi- dates for exploring quantum fluids, since they can be manufactured reproducibly, cover the frequency range from hundreds of kilohertz up to gigahertz and usually have very low power dissipation. Their small size offers the possibility of probing the condensate on scales comparable to, and below, the coherence length. That said, there have been hitherto no successful measurements of NEMS res- onators in the liquid phases of helium. Here we report the operation of doubly-clamped aluminum nanocantilevers in superfluid 4He at temperatures spanning the superfluid transition. The devices are shown to be very sensitive detectors of the superfluid density and the normal fluid damping. We use nanomechanical resonators with extremely high quality factor to probe superfluid 4He at millikelvin temperatures, as well. The high sensitivity of these devices to thermal excitations in the environment makes it possible to drive them using the mo- mentum transfer from phonons generated by a nearby heater. This so-called phonon wind is a reverse thermomechanical effect that until now has never been demonstrated.