Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anomalous low-frequency conductivity in easy-plane XXZ spin chains   In the easy-plane regime of XXZ spin chains, spin transport is ballistic,
with a Drude weight that has a discontinuous fractal dependence on the value of
the anisotropy $\Delta = \cos \pi \lambda$ at nonzero temperatures. We show
that this structure necessarily implies the divergence of the low-frequency
conductivity for generic irrational values of $\lambda$. Within the framework
of generalized hydrodynamics, we show that in the high-temperature limit the
low-frequency conductivity at a generic anisotropy scales as $\sigma(\omega)
\sim 1/\sqrt{\omega}$; anomalous response occurs because quasiparticles undergo
L\'evy flights. For rational values of $\lambda$, the divergence is cut off at
low frequencies and the corrections to ballistic spin transport are diffusive.
We also use our approach to recover that at the isotropic point $\Delta=1$,
spin transport is superdiffusive with $\sigma(\omega) \sim \omega^{-1/3}$. We
support our results with extensive numerical studies using matrix-product
operator methods.

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The categories of this paper are: cs
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The categories of this paper are: physics
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: math
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The categories of this paper are: dg-ga