Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superfluid Breakdown and Multiple Roton Gaps in Spin-Orbit Coupled
  Bose-Einstein Condensates on an Optical Lattice   We investigate the superfluid phases of a Rashba spin-orbit coupled
Bose-Einstein condensate residing on a two dimensional square optical lattice
in the presence of an effective Zeeman field $\Omega$. At a critical value
$\Omega=\Omega_c$, the single-particle spectrum $ E_k $ changes from having a
set of four degenerate minima to a single minimum at $k=0$, corresponding to
condensation at finite or zero momentum, respectively. We describe this quantum
phase transition and the symmetry breaking of the condensate phases. We use the
Bogoliubov theory to treat the superfluid phases and determine the phase
diagram, the excitation spectrum and the sound velocity of the phonon
excitations. A novel dynamically unstable superfluid regime occurring when
$\Omega$ is close to $\Omega_c$ is analytically identified and the behavior of
the condensate quantum depletion is discussed. Moreover, we show that there are
two types of roton excitations occurring in the $\Omega<\Omega_c$ regime and
obtain explicit values for the corresponding energy gaps.

19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat