title: Orbitally driven spin-singlet dimerization in S=1 La4Ru2O10.
abstract: Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation + Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.
authors.affiliation: II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
authors.forename: Hua
authors.initials: H
authors.lastname: Wu
authors.forename: Z
authors.initials: Z
authors.lastname: Hu
authors.forename: T
authors.initials: T
authors.lastname: Burnus
authors.forename: J D
authors.initials: JD
authors.lastname: Denlinger
authors.forename: P G
authors.initials: PG
authors.lastname: Khalifah
authors.forename: D G
authors.initials: DG
authors.lastname: Mandrus
authors.forename: L-Y
authors.initials: LY
authors.lastname: Jang
authors.forename: H H
authors.initials: HH
authors.lastname: Hsieh
authors.forename: A
authors.initials: A
authors.lastname: Tanaka
authors.forename: K S
authors.initials: KS
authors.lastname: Liang
authors.forename: J W
authors.initials: JW
authors.lastname: Allen
authors.forename: R J
authors.initials: RJ
authors.lastname: Cava
authors.forename: D I
authors.initials: DI
authors.lastname: Khomskii
authors.forename: L H
authors.initials: LH
authors.lastname: Tjeng