title: The paired-electron crystal in the two-dimensional frustrated quarter-filled band.
abstract: The competition between antiferromagnetic and spin-singlet ground states within quantum spin models and the ½-filled band Hubbard model has received intense scrutiny. Here we demonstrate a frustration-induced transition from Néel antiferromagnetism to a spin-singlet state in the interacting ¼-filled band on an anisotropic triangular lattice. While the antiferromagnetic state has equal charge densities, 0.5, on all sites, the spin-singlet state is a paired-electron crystal, with pairs of charge-rich sites separated by pairs of charge-poor sites. The paired-electron crystal provides a natural description of the spin-gapped state proximate to superconductivity in many organic charge transfer solids. Pressure-induced superconductivity in these correlated-electron systems is likely a result of a transition from the ¼-filled band valence bond solid to a valence bond liquid.
authors.affiliation: Department of Physics, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: R T
authors.initials: RT
authors.lastname: Clay
authors.forename: S
authors.initials: S
authors.lastname: Mazumdar