Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Vertical Position of Sr Dopants in the Sr$_x$Bi$_2$Se$_3$
  Superconductor   The discovery of topological superconductivity in doped Bi$_2$Se$_3$ made
this class of materials highly important for the field of condensed matter
physics. However, the structural origin of the superconducting state remained
elusive, despite being investigated intensively in recent years. We use
scanning tunneling microscopy and the normal incidence x-ray standing wave
(NIXSW) technique in order to determine the vertical position of the dopants --
one of the key parameters for understanding topological superconductivity in
this material -- for the case of Sr$_{x}$Bi$_2$Se$_3$. In a novel approach we
analyze the NIXSW data in consideration of the inelastic mean free path of the
photoemitted electrons, which allows us to distinguish between symmetry
equivalent sites. We find that Sr-atoms are not situated inside the van der
Waals gap between the Bi$_2$Se$_3$ quintuple layers but rather in the quintuple
layer close to the outer Se planes.

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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: econ
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
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The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
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The categories of this paper are: bayes-an
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
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The categories of this paper are: eess