Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Orbital and spin effects for the upper critical field in As deficient
  disordered Fe pnictide superconductors   We report B_c2 data for LaO_{0.9}F_{0.1}FeAs_{1-delta} in a wide T and field
range up to 60 Tesla. The large slope of B_c2 approx ~ -6 Tesla/K near an
improved T_c = 28.5 K of the in-plane B_c2(T) contrasts with a flattening
starting at 23 K above 30 Tesla we regard as the onset of Pauli-limited
behavior (PLB) with B_c2(0) about 65 Tesla. We interpret a similar hitherto
unexplained flattening of the B_c2(T) curves reported for at least three other
disordered closely related systems as also as a manifestation of PLB. Their
Maki parameters have been estimated analyzing their B_c2(T) data within the WHH
approach. The pronounced PLB of (Ba,K)Fe_2As_2 single crystals from a tin-flux
is attributed also to a significant As deficiency. Consequences of our results
are discussed in terms of disorder effects within conventional (CSC) and
unconventional superconductivity (USC). USC scenarios with nodes on individual
Fermi surface sheets (FSS), can be discarded for our samples. The increase of
dB_c2/dT|_{T_c} by sizeable disorder provides evidence for an important
intraband (intra-FSS) contribution to the orbital upper critical field. We
suggest that it can be ascribed either to an impurity driven transition from
s_{+-} USC to CSC of an extended s_{++}-wave state or to a stabilized
s_{+-}-state provided As-vacancies cause predominantly strong intraband
scattering in the unitary limit. We compare our results with B_c2 data from the
literature with no PLB for fields below 60 to 70 Tesla probed so far. A novel
disorder related scenario of a complex interplay of SC with two different
competing magnetic instabilities is suggested.

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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: econ
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The categories of this paper are: cs
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-ex
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The categories of this paper are: plasm-ph