Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Excitonic instability in optically-pumped three-dimensional Dirac
  materials   Recently it was suggested that transient excitonic instability can be
realized in optically-pumped two-dimensional (2D) Dirac materials (DMs), such
as graphene and topological insulator surface states. Here we discuss the
possibility of achieving a transient excitonic condensate in optically-pumped
three-dimensional (3D) DMs, such as Dirac and Weyl semimetals, described by
non-equilibrium chemical potentials for photoexcited electrons and holes.
Similar to the equilibrium case with long-range interactions, we find that for
pumped 3D DMs with screened Coulomb potential two possible excitonic phases
exist, an excitonic insulator phase and the charge density wave phase
originating from intranodal and internodal interactions, respectively. In the
pumped case, the critical coupling for excitonic instability vanishes;
therefore, the two phases coexist for arbitrarily weak coupling strengths. The
excitonic gap in the charge density wave phase is always the largest one. The
competition between screening effects and the increase of the density of states
with optical pumping results in a reach phase diagram for the transient
excitonic condensate. Based on the static theory of screening, we find that
under certain conditions for the value of the dimensionless coupling constant
screening in 3D DMs can be weaker than in 2D DMs. Furthermore, we identify the
signatures of the transient excitonic condensate that could be probed by
scanning tunneling spectroscopy, photoemission and optical conductivity
measurements. Finally, we provide estimates of critical temperatures and
excitonic gaps for existing and hypothetical 3D DMs.

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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
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The categories of this paper are: math
30
The categories of this paper are: q-alg
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: physics
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The categories of this paper are: patt-sol
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The categories of this paper are: astro-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: q-fin