Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Semi-metal-insulator transition on the surface of a topological
  insulator with in-plane magnetization   A thin film of ferromagnetically ordered material proximate to the surface of
a three-dimensional topological insulator explicitly breaks the time-reversal
symmetry of the surface states. For an out-of-plane ferromagnetic order
parameter on the surface, the parity is also broken, since the Dirac fermions
become massive. This leads in turn to the generation of a topological
Chern-Simons term by quantum fluctuations. On the other hand, for an in-plane
magnetization the surface states remain gapless for the non-interacting Dirac
fermions. In this work we study the possibility of spontaneous breaking of
parity due to a dynamical gap generation on the surface in the presence of a
local, Hubbard-like, interaction of strength $g$ between the Dirac fermions. A
gap and a Chern-Simons term are generated for $g$ larger than some critical
value, g_c, provided the number of Dirac fermions, $N$, is odd. For an even
number of Dirac fermions the masses are generated in pairs having opposite
signs, and no Chern-Simons term is generated. We discuss our results in the
context of recent experiments in EuS/Bi_2Se_3 heterostructures.

10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
1
The categories of this paper are: cs