Probing superfluid He-4 with high-frequency nanomechanical resonators down to mK temperatures

The data set for the paper "Probing superfluid He-4 with
high-frequency nanomechanical resonators down to mK temperatures"
accepted for publication in PRB. Abstract: Superfluids, such as superfluid
He-3 and He-4, exhibit a broad range of quantum phenomena and excitations
which are unique to these systems. Nanoscale mechanical resonators are
sensitive and versatile force detectors with the ability to operate over
many orders of magnitude in damping. Using nanomechanical-doubly clamped
beams of extremely high-quality factors Q>1e6, we probe superfluid He-4
from the superfluid transition temperature down to mK temperatures at
frequencies up to 11.6 MHz. Our studies show that nanobeam damping is
dominated by hydrodynamic viscosity of the normal component of He-4 above
1K. In the temperature range 0.3-0.8K, the ballistic quasiparticles
(phonons and rotons) determine the beams' behavior. At lower
temperatures, damping saturates and is determined either by magnetomotive
losses or acoustic emission into helium. It is remarkable that all these
distinct regimes can be extracted with just a single device, despite
damping changing over six orders of magnitude.