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  Kimber, S.A.J.; Senn, M.S.; Fratini, S.; Wu, H.; Hill, A.H.; Manuel, P.; Attfield, J.P.; Argyriou, D.N.; Henry, P.F.: Charge Order at the Frontier between the Molecular and Solid States in Ba₃NaRu₂O₉. Physical Review Letters 108 (2012), p. 217205

10.1103/PhysRevLett.108.217205
Open Access Version (externer Anbieter)

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.