Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Drude and Superconducting Weights and Mott Transitions in Variation
  Theory   Drude weight ($D$) is a useful measure to distinguish a metal from an
insulator. However, $D$ has not been justifiably estimated by the variation
theory for long, since Millis and Coppersmith [Phys. Rev. B 43 (1991) 13770]
pointed out that a variational wave function $\Psi_Q$, which includes the key
ingredient (doublon-holon binding effect) for a Mott transition, yields a
positive $D$ (namely metallic) even in the Mott-insulating regime. We argue
that, to obtain a correct $D$, an imaginary part must exist in the wave
function. By introducing a configuration-dependent phase factor ${\cal
P}_\theta$ to $\Psi_Q$, Mott transitions are successfully represented by $D$
($D=0$ for $U>U_{\rm c}$) for a normal and $d$-wave pairing states; thereby,
the problem of Millis and Coppersmith is settled. Generally, ${\cal P}_\theta$
plays a pivotal role in describing current-carrying states in regimes of Mott
physics. On the other hand, we show using a perturbation theory, the one-body
(mean-field) part of the wave function should be complex for band insulators
such as antiferromagnetic states in hypercubic lattices.

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The categories of this paper are: econ
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: physics
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The categories of this paper are: hep-ex
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The categories of this paper are: stat