Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superluminal Tachyonlike Excitations of Dirac Fermions in a Topological
  Insulator Junction   We have considered a system of two topological insulators and have determined
the properties of the surface states at the junction. Here we report that these
states, under certain conditions exhibit superluminous (tachyonic) dispersion
of the Dirac fermions. Although superluminal excitations are known to exist in
optical systems, this is the first demonstration of possible tachyonic
excitations in a purely electronic system. The first ever signature of tachyons
could therefore be found experimentally in a topological insulator junction.

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The categories of this paper are: physics
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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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: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio