Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Probing superfluid $^4\mathrm{He}$ with high-frequency nanomechanical
  resonators down to $\mathrm{mK}$ temperatures   Superfluids, such as superfluid $^3\mathrm{He}$ and $^4\mathrm{He}$, 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
($Q>10^6$), we probe superfluid $^4\mathrm{He}$ from the superfluid transition
temperature down to $\mathrm{mK}$ temperatures at frequencies up to $11.6 \,
\mathrm{MHz}$. Our studies show that nanobeam damping is dominated by
hydrodynamic viscosity of the normal component of $^4\mathrm{He}$ above
$1\,\mathrm{K}$. In the temperature range $0.3-0.8\,\mathrm{K}$, 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.

36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
3
The categories of this paper are: physics
1
The categories of this paper are: cs
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The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph