Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electronic Transport in Hybrid Mesoscopic Structures: A Nonequilibrium
  Green Function Approach   We present a unified transport theory of hybrid structures, in which a
confined normal state ($N$) sample is sandwiched between two leads each of
which can be either a ferromagnet ($F$) or a superconductor ($S$) via tunnel
barriers. By introducing a four-dimensional Nambu-spinor space, a general
current formula is derived within the Keldysh nonequilibrium Green function
formalism, which can be applied to various kinds of hybrid mesoscopic systems
with strong correlations even in the nonequilibrium situation. Such a formula
is gauge invariant. We also demonstrate analytically for some quantities, such
as the difference between chemical potentials, superconductor order parameter
phases and ferromagnetic magnetization orientations, that only their relative
value appears explicitly in the current expression. When applied to specific
structures, the formula becomes of the Meir-Wingreen-type favoring strong
correlation effects, and reduces to the Landauer-B\"uttiker-type in
noninteracting systems such as the double-barrier resonant structures, which we
study in detail beyond the wide-band approximation.

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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
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The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
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The categories of this paper are: econ
16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
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The categories of this paper are: chem-ph