title: Charge order at the frontier between the molecular and solid states in Ba3NaRu2O9.
abstract: We show that the valence electrons of Ba3NaRu2O9, which has a quasimolecular structure, completely crystallize below 210 K. Using an extended Hubbard model, we show that the charge ordering instability results from long-range Coulomb interactions. However, orbital ordering, metal-metal bonding, and formation of a partial spin gap enforce the magnitude of the charge separation. The striped charge order and frustrated hcp lattice of Ru2O9 dimers lead to competition with a quasidegenerate charge-melted phase under photoexcitation at low temperature. Our results establish a broad class of simple metal oxides as models for emergent phenomena at the border between the molecular and solid states.
authors.affiliation: European Synchrotron Radiation Facility (ESRF), Grenoble, France. kimber@esrf.fr
authors.forename: Simon A J
authors.initials: SA
authors.lastname: Kimber
authors.forename: Mark S
authors.initials: MS
authors.lastname: Senn
authors.forename: Simone
authors.initials: S
authors.lastname: Fratini
authors.forename: Hua
authors.initials: H
authors.lastname: Wu
authors.forename: Adrian H
authors.initials: AH
authors.lastname: Hill
authors.forename: Pascal
authors.initials: P
authors.lastname: Manuel
authors.forename: J Paul
authors.initials: JP
authors.lastname: Attfield
authors.forename: Dimitri N
authors.initials: DN
authors.lastname: Argyriou
authors.forename: Paul F
authors.initials: PF
authors.lastname: Henry