Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for an excitonic insulator phase in a zero-gap InAs/GaSb
  bilayer   Many-body interactions can produce novel ground states in a condensed-matter
system. For example, interacting electrons and holes can spontaneously form
excitons, a neutral bound state, provided that the exciton binding energy
exceeds the energy separation between the single particle states. Here we
report on electrical transport measurements on spatially separated
two-dimensional electron and hole gases with nominally degenerate energy
subbands, realized in an InAs(10 nm)/GaSb(5 nm) coupled quantum well. We
observe a narrow and intense maximum (~500 k\Omega) in the four-terminal
resistivity in the charge neutrality region, separating the electron-like and
hole-like regimes, with a strong activated temperature-dependence above T = 7 K
and perfect stability against quantizing magnetic fields. By quantitatively
comparing our data with early theoretical predictions, we show that such
unexpectedly large resistance in our nominally zero-gap semi-metal system is
probably due to the formation of an excitonic insulator state.

12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom