Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Small Energy Gap Revealed in CrBr3 by Scanning Tunneling Spectroscopy   CrBr$_{3}$ is a layered van der Waals material with magnetic ordering down to
the 2D limit. For decades, based on optical measurements, it is believed that
the energy gap of CrBr$_{3}$ is in the range of 1.68-2.1 eV. However,
controversial results have indicated that the band gap of CrBr$_{3}$ is
possibly smaller than that. An unambiguous determination of the energy gap is
critical to the correct interpretations of the experimental results of
CrBr$_{3}$. Here, we present the scanning tunneling microscopy and spectroscopy
(STM/S) results of CrBr$_{3}$ thin and thick flakes exfoliated onto pyropytic
graphite (HOPG) surfaces and density functional theory (DFT) calculations to
reveal the small energy gap (peak-to-peak energy gap to be 0.57 eV $\pm$ 0.04
eV; or the onset signal energy gap to be 0.29 $\pm$ 0.05 eV from dI/dV
spectra). Atomic resolution topography images show the defect-free crystal
structure and the dI/dV spectra exhibit multiple peak features measured at 77
K. The conduction band - valence band peak pairs in the multi-peak dI/dV
spectrum agree very well with all reported optical transitions. STM topography
images of mono- and bi-layer CrBr$_{3}$ flakes exhibit edge degradation due to
short air exposure (~15 min) during sample transfer. The unambiguously
determined small energy gap settles the controversy and is the key in better
understanding CrBr$_{3}$ and similar materials.

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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: cs
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The categories of this paper are: math
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The categories of this paper are: astro-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: ao-sci
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con