Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Excitation-induced transition to indirect band gaps in atomically thin
  transition metal dichalcogenide semiconductors   Monolayers of transition metal dichalcogenides (TMDCs) exhibit an
exceptionally strong Coulomb interaction between charge carriers due to the
two-dimensional carrier confinement in connection with weak dielectric
screening. High densities of excited charge carriers in the various
band-structure valleys cause strong many-body renormalizations that influence
both the electronic properties and the optical response of the material. We
investigate electronic and optical properties of the typical monolayer TMDCs
MoS$_2$, MoSe$_2$, WS$_2$ and WSe$_2$ in the presence of excited carriers by
solving semiconductor Bloch equations on the full Brillouin zone. With
increasing carrier density, we systematically find a reduction of the exciton
binding energies due to Coulomb screening and Pauli blocking. Together with
excitation-induced band-gap shrinkage this leads to redshifts of excitonic
resonances up to the dissociation of excitons. As a central result, we predict
for all investigated monolayer TMDCs that the $\Sigma$-valley shifts stronger
than the K-valley. Two of the materials undergo a transition from direct to
indirect band gaps under carrier excitation similar to well-known
strain-induced effects. Our findings have strong implications for the filling
of conduction-band valleys with excited carriers and are relevant to transport
and optical applications as well as the emergence of phonon-driven
superconductivity.

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The categories of this paper are: atom-ph
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The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys