Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Novel Superconducting Characteristics and Unusual Normal-State
  Properties in Iron-based Pnictide Superconductors: 57Fe-NMR and 75As-NQR/NMR
  studies in REFeAsO_1-y (RE=La,Pr,Nd) and Ba0.6K0.4Fe2As2   We discuss the novel superconducting characteristics and unusual normal-state
properties of iron (Fe)-based pnictide superconductors REFeAsO$_{1-y}$
(RE=La,Pr,Nd) and Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$($T_{c}=$ 38 K) by means of
$^{57}$Fe-NMR and $^{75}$As-NQR/NMR. In the superconducting state of
LaFeAsO$_{0.7}$ ($T_{c}=$ 28 K), the spin component of the $^{57}$Fe-Knight
shift decreases to almost zero at low temperatures, which provide firm evidence
of the superconducting state formed by spin-singlet Cooper pairing. The nuclear
spin-lattice relaxation rates $(1/T_{1})$ in LaFeAsO$_{0.7}$ and
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ exhibit a $T^{3}$-like dependence without a
coherence peak just below $T_{c}$, indicating that an unconventional
superconducting state is commonly realized in these Fe-based pnictide
compounds. All these events below $T_c$ are consistently argued in terms of an
extended s$_{\pm}$-wave pairing with a sign reversal of the order parameter
among Fermi surfaces. In the normal state, $1/T_1T$ decreases remarkably upon
cooling for both the Fe and As sites of LaFeAsO$_{0.7}$. In contrast, it
gradually increases upon cooling in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. Despite
the similarity between the superconducting properties of these compounds, a
crucial difference was observed in their normal-state properties depending on
whether electrons or holes are doped into the FeAs layers. These results may
provide some hint to address a possible mechanism of Fe-based pnictide
superconductors.

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The categories of this paper are: astro-ph
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The categories of this paper are: math
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: math-ph
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph
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The categories of this paper are: nlin
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: adap-org
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat