Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of Wannier-Stark localization at the surface of BaTiO$_3$
  films by photoemission   Observation of Bloch oscillations and Wannier-Stark localization of charge
carriers is typically impossible in single-crystals, because an electric field
higher than the breakdown voltage is required. In BaTiO$_3$ however, high
intrinsic electric fields are present due to its ferroelectric properties. With
angle-resolved photoemission we directly probe the Wannier-Stark localized
surface states of the BaTiO$_3$ film-vacuum interface and show that this effect
extends to thin SrTiO$_3$ overlayers. The electrons are found to be localized
along the in-plane polarization direction of the BaTiO$_3$ film.

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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: stat
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The categories of this paper are: q-fin
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: econ