Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analytical results for the low-temperature Drude weight of the XXZ spin
  chain   The spin-$1/2$ XXZ chain is an integrable lattice model and parts of its spin
current can be protected by local conservation laws for anisotropies
$-1<\Delta<1$. In this case, the Drude weight $D(T)$ is non-zero at finite
temperatures $T$. Here we obtain analytical results for $D(T)$ at low
temperatures for zero external magnetic field and anisotropies
$\Delta=\cos(n\pi/m)$ with $n,m$ coprime integers, using the thermodynamic
Bethe ansatz. We show that to leading orders
$D(T)=D(0)-a(\Delta)T^{2K-2}-b_1(\Delta)T^2$ where $K$ is the Luttinger
parameter and the prefactor $a(\Delta)$, obtained in closed form, has a fractal
structure as function of anisotropy $\Delta$. The prefactor $b_1(\Delta)$, on
the other hand, does not have a fractal structure and can be obtained in a
standard field-theoretical approach. Including both temperature corrections, we
obtain an analytic result for the low-temperature asymptotics of the Drude
weight in the entire regime $-1<\Delta=\cos(n\pi/m)<1$.

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The categories of this paper are: hep-ex
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: eess
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The categories of this paper are: astro-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math
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The categories of this paper are: econ
32
The categories of this paper are: atom-ph