Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermodynamically activated vortex-dipole formation in a two-dimensional
  Bose-Einstein condensate   Three distinct types of behaviour have recently been identified in the
two-dimensional trapped bosonic gas, namely; a phase coherent Bose-Einstein
condensate (BEC), a Berezinskii-Kosterlitz-Thouless-type (BKT) superfluid and
normal gas phases in order of increasing temperature. In the BKT phase the
system favours the formation of vortex-antivortex pairs, since the free energy
is lowered by this topological defect. We provide a simple estimate of the free
energy of a dilute Bose gas with and without such vortex dipole excitations and
show how this varies with particle number and temperature. In this way we can
estimate the temperature for cross-over from the coherent BEC to the (only)
locally ordered BKT-like phase by identifying when vortex dipole excitations
proliferate. Our results are in qualitative agreement with recent, numerically
intensive, classical field simulations.

1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th