title: Creation and destruction of a spin gap in weakly coupled quarter-filled ladders.
abstract: We investigate weakly coupled quarter-filled ladders with model parameters relevant for NaV(2)O(5) using density-matrix renormalization group calculations on an extended Hubbard model coupled to the lattice. NaV(2)O(5) exhibits super-antiferroelectric charge order with a zigzag pattern on each ladder. We show that this order causes a spin dimerization along the ladder and is accompanied by a spin gap of the same magnitude as that observed experimentally. The spin gap is destroyed again at large charge order due to a restructuring of the spins. An analysis of an effective spin model predicts a recreation of the gap by interladder singlets when the charge order increases further.
authors.affiliation: Institut für Theoretische Physik, Technische Universität Graz, A-8010 Graz, Austria.
authors.forename: B
authors.initials: B
authors.lastname: Edegger
authors.forename: H G
authors.initials: HG
authors.lastname: Evertz
authors.forename: R M
authors.initials: RM
authors.lastname: Noack