Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fate of the excitonic insulator in the presence of phonons   The influence of phonons on the formation of the excitonic insulator has
hardly been analyzed so far. Recent experiments on $\rm Ta_2NiSe_5$, 1$T$-$\rm
TiSe_2$, and $\rm TmSe_{0.45}Te_{0.55}$, being candidates for realizing the
excitonic-insulator state, suggest, however, that the underlying lattice plays
a significant role. Employing the Kadanoff-Baym approach we address this issue
theoretically. We show that owing to the electron-phonon coupling a static
lattice distortion may arise at the excitonic instability. Most importantly
such a distortion will destroy the acoustic phase mode being present if the
electron-hole pairing and condensation is exclusively driven by the Coulomb
interaction. The absence of off-diagonal long-range order, when lattice degrees
of freedom are involved, challenges that excitons in these materials form a
superfluid condensate of Bose particles or Cooper pairs composed of electrons
and holes.

5
The categories of this paper are: gr-qc
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph