Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phase diagram of the 2D $^4$He in the density-temperature plane   Thin $^4$He films adsorbed to weakly attractive substrates form nearly 2D
layers. We describe the vortices in 2D superfluid $^4$He like quasiparticles.
With the aid of a variational many-body calculation we estimate their inertial
mass and describe their interactions with the $^4$He particles and other
vortices. Third sound measurements revealed anomalous behavior below the
BKT-phase transition temperature. We ascribe this to the sound mode traveling
in the fluid of vortex-antivortex pairs. These pairs forms a crystal (or liquid
crystal) when the film thickness increases, the third sound mode splits into
two separate modes as seen in experiments. Our many-body calculation predicts
the critical density, at which the phase transition into the vortex-antivortex
state at zero temperature occurs. We also describe the phase diagram of thin
$^4$He films.

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The categories of this paper are: stat
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph