Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum phase transition in a two-dimensional system of dipoles   The ground-state phase diagram of a two-dimensional Bose system with
dipole-dipole interactions is studied by means of quantum Monte Carlo
technique. Our calculation predicts a quantum phase transition from gas to
solid phase when the density increases. In the gas phase the condensate
fraction is calculated as a function of the density. Using Feynman
approximation, the collective excitation branch is studied and appearance of a
roton minimum is observed. Results of the static structure factor at both sides
of the gas-solid phase are also presented. The Lindeman ratio at the transition
point comes to be $\gamma = 0.230(6)$. The condensate fraction in the gas phase
is estimated as a function of the density.

36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
2
The categories of this paper are: math
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas