Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structural and electronic properties of the Nb$_4$-cluster compound
  Ga$_{1.33}$Nb$_4$X$_8$ (X = S, Se)   We report resistivity, thermopower and magnetic susceptibility measurements
on the Nb$_4$-cluster compounds Ga$_{1.33}$Nb$_4$X$_{8}$ (X = S, Se), derived
from vacancy ordered spinels A$_x$T$_4$X$_8$. The cubic selenide phase is
insulating and its resistivity crosses over from $\ln{\rho} \sim T^{-1}$ to
$\sim T^{-1/2}$ on cooling below 150 K, indicating variable range hopping (VRH)
conduction at low temperatures. This is similar to that previously reported for
V$_4$ and Mo$_4$ cluster compounds. The rhombohedrally distorted sulfide is
metallic and shows a minimum in resistance at $\sim $ 56 K below which the
resistivity varies as $\rho(T) \sim T^{-1/2}$. The thermopower of the selenide
becomes temperature independent below the crossover temperature. These Nb$_4$
compounds exhibit enhanced Pauli-paramagnetic magnetic susceptibility ($\chi$)
irrespective of their transport properties and both undergo a similar
transition in $\chi(T) \sim 30$ K. We discuss these properties in the model of
hopping conduction under long-range Coulomb repulsion effects and derive
consistency between some of the transport and magnetic parameters.

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The categories of this paper are: supr-con
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: nlin
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The categories of this paper are: nucl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg