Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral properties of periodic systems cut at an angle   We consider a semi-periodic two-dimensional Schr\"odinger operator which is
cut at an angle. When the cut is commensurate with the periodic lattice, the
spectrum of the operator has the band-gap Bloch structure. We prove that in the
incommensurable case, there are no gaps: the gaps of the bulk operator are
filled with edge spectrum.

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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: q-fin
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-th
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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: chem-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-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