Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Directly visualizing the momentum forbidden dark excitons and their
  dynamics in atomically thin semiconductors   Resolving the momentum degree of freedom of excitons - electron-hole pairs
bound by the Coulomb attraction in a photoexcited semiconductor, has remained a
largely elusive goal for decades. In atomically thin semiconductors, such a
capability could probe the momentum forbidden dark excitons, which critically
impact proposed opto-electronic technologies, but are not directly accessible
via optical techniques. Here, we probe the momentum-state of excitons in a WSe2
monolayer by photoemitting their constituent electrons, and resolving them in
time, momentum and energy. We obtain a direct visual of the momentum forbidden
dark excitons, and study their properties, including their near-degeneracy with
bright excitons and their formation pathways in the energy-momentum landscape.
These dark excitons dominate the excited state distribution - a surprising
finding that highlights their importance in atomically thin semiconductors.

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The categories of this paper are: astro-ph
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The categories of this paper are: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: physics
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The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: q-bio