Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Critical charge fluctuations and emergent coherence in a strongly
  correlated excitonic insulator   Excitonic insulator is a coherent electronic phase that results from the
formation of a macroscopic population of bound particle-hole pairs - excitons.
With only a few candidate materials known, the collective excitonic behavior is
challenging to observe, being obscured by crystalline lattice effects. Here we
use polarization-resolved Raman spectroscopy to reveal the quadrupolar
excitonic mode in the candidate zero-gap semiconductor Ta$_2$NiSe$_5$
disentangling it from the lattice phonons. The excitonic mode pronouncedly
softens close to the phase transition, showing its electronic character, while
its coupling to non-critical lattice modes is shown to enhance the transition
temperature. On cooling, we observe the gradual emergence of coherent
superpositions of band states at the correlated insulator gap edge, with strong
departures from mean-field theory predictions. Our results demonstrate the
realization of a strongly correlated excitonic state in an equilibrium bulk
material.

6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg