Probing Bogoliubov quasiparticles in superfluid $^3$He with a 'vibrating-wire like' MEMS device

TL;DR

This study investigates the interaction between superfluid helium-3 and a MEMS device, revealing nonlinear damping behavior, a critical velocity for Cooper-pair breaking, and nonlinear resonance effects linked to quasiparticle friction.

Contribution

It introduces a MEMS device for probing superfluid helium-3 and demonstrates its effectiveness in measuring quasiparticle interactions and nonlinear damping phenomena.

Findings

Damping follows theory for vibrating wires due to Andreev reflection.

Critical velocity for increased damping is 2.6 m/s, lower than other probes.

Nonlinear resonance shape suggests inertial effects from quasiparticle friction.

Abstract

We have measured the interaction between superfluid $^3$He-B and a micro-machined goalpost-shaped device at temperatures below $0.2\,T_c$. The measured damping follows well the theory developed for vibrating wires, in which the Andreev reflection of quasiparticles in the flow field around the moving structure leads to a nonlinear frictional force. At low velocities the damping force is proportional to velocity while it tends to saturate for larger excitations. Above a velocity of 2.6$\,$mms$^{-1}$ the damping abruptly increases, which is interpreted in terms of Cooper-pair breaking. Interestingly, this critical velocity is significantly lower than reported with other mechanical probes immersed in superfluid $^3$He. Furthermore, we report on a nonlinear resonance shape for large motion amplitudes that we interpret as an inertial effect due to quasiparticle friction, but other mechanisms could possibly be invoked as well.