Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: From charge- and spin-ordering to superconductivity in the organic
  charge-transfer solids   We review recent progress in understanding the different spatial broken
symmetries that occur in the normal states of the family of charge-transfer
solids (CTS) that exhibit superconductivity (SC), and discuss how this
knowledge gives insight to the mechanism of the unconventional SC in these
systems. We show that a unified theory of the diverse broken symmetry states
necessarily requires explicit incorporation of strong electron-electron
interactions and lattice discreteness, and most importantly, the correct
bandfilling of one-quarter. Uniquely in the quarter-filled band, there is a
very strong tendency to form nearest neighbor spin-singlets, in both one and
two dimensions. The tendency to spin-singlets, a quantum effect, drives a
commensurate charge-order in the correlated quarter-filled band. This
charge-ordered spin-singlet, which we label as a paired-electron crystal (PEC),
is different from and competes with both the antiferromagnetic state and the
Wigner crystal of single electrons. Further, unlike these classical broken
symmetries, the PEC is characterized by a spin gap. The tendency to the PEC in
two dimensions is enhanced by lattice frustration. Following this
characterization of the spatial broken symmetries, we critically reexamine
spin-fluctuation and resonating valence bond theories of frustration-driven SC
within half-filled band Hubbard and Hubbard-Heisenberg Hamiltonians for the
superconducting CTS. We develop a valence-bond theory of SC within which the
superconducting state is reached by the destabilization of the PEC by
additional pressure-induced lattice frustration that makes the spin-singlets
mobile. Our proposed mechanism for SC is the same for CTS in which the
proximate semiconducting state is antiferromagnetic instead of charge-ordered,
with the only difference that SC in the former is generated via a fluctuating
spin-singlet state as opposed to static PEC.

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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: math
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph