Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coulomb Gap: How a Metal Film Becomes an Insulator   Electron tunneling measurements of the density of states (DOS) in ultra-thin
Be films reveal that a correlation gap mediates their insulating behavior. In
films with sheet resistance $R<5000\Omega$ the correlation singularity appears
as the usual perturbative $ln(V)$ zero bias anomaly (ZBA) in the DOS. As R is
increased further, however, the ZBA grows and begins to dominate the DOS
spectrum. This evolution continues until a non-perturbative $|V|$
Efros-Shklovskii Coulomb gap spectrum finally emerges in the highest R films.
Transport measurements of films which display this gap are well described by a
universal variable range hopping law $R(T)=(h/2e^2)exp(T_o/T)^{1/2}$.

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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: stat
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The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: supr-con
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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: bayes-an
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The categories of this paper are: chem-ph