Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Kondo screening cloud: what it is and how to observe it   The Kondo effect involves the formation of a spin singlet by a magnetic
impurity and conduction electrons. It is characterized by a low temperature
scale, the Kondo temperature, $T_K$, and an associated long length scale,
$\xi_K = \hbar v_F/(k_BT_K)$ where $v_F$ is the Fermi velocity. This Kondo
length is often estimated theoretically to be in the range of .1 to 1 microns
but such a long characteristic length scale has never been observed
experimentally. In this review, I will examine how $\xi_K$ appears as a
crossover scale when one probes either the dependence of physical quantities an
distance from the impurity or when the impurity is embedded in a finite size
structure and discuss possible experiments that might finally observe this
elusive length scale.

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The categories of this paper are: q-alg
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The categories of this paper are: astro-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph