Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Fermi surface of Na$_{x}$CoO$_2$   Doping evolution of the Fermi surface topology of Na$_x$CoO$_2$ is studied
systematically. Both local density approximation (LDA) and local spin density
approximation (LSDA) predict a large Fermi surface as well as small hole
pockets for doping levels $x\sim$ 0.5. In contrast, the hole pockets are
completely absent for all doping levels within LSDA+U. More importantly, we
find no violation of Luttinger's rule in this system, contrary to a recent
suggestion. The measured Fermi surface of Na$_{0.7}$CoO$_2$ can be explained by
its half-metallic behavior and agrees with our LSDA+U calculations.

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The categories of this paper are: comp-gas
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: plasm-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg