Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of an anomalous density-dependent energy gap of the
  $\nu=5/2$ fractional quantum Hall state in the low density regime   We have studied the $\nu=5/2$ fractional quantum Hall state in a
density-tunable sample at extremely low electron densities. For the densities
accessed in our experiment, the Landau level mixing parameter $\kappa$ spans
the $2.52<\kappa<2.82$ range. In the vicinity of $5.8 \times 10^{10}$~cm$^{-2}$
or $\kappa = 2.6$ an anomalously large change in the density dependence of the
energy gap is observed. Possible origins of such an anomaly are discussed,
including a topological phase transition in the $\nu=5/2$ fractional quantum
Hall state.

15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio