title: Spin gap in Tl2Ru2O7 and the possible formation of Haldane chains in three-dimensional crystals.
abstract: Dimensionality is one of the most important parameters of physical phenomena. Only two things determine the universality class of a phase transition: the dimensionality of a given system and the symmetry of the order parameter. In most cases, the dimensionality of a substance is predetermined by its crystal structure. Examples in which the effective dimensionality is reduced are quite rare. Here we show that the three-dimensional cubic system of Tl(2)Ru(2)O(7) most probably evolves into a one-dimensional spin-one Haldane system with a spin gap below 120 K, accompanied by anomalies in the structure, resistivity and susceptibility. We argue that these anomalies are due to an orbital ordering of Ru 4d electrons, with a strong coupling among three degrees of freedom: orbital, spin and lattice. Our work provides a unique example of the spontaneous formation of Haldane system with an insight into the intriguing interplay of different degrees of freedom.
authors.affiliation: Department of Physics and Institute of Basic Science, SungKyunKwan University, Suwon 440-746, Korea.
authors.forename: Seongsu
authors.initials: S
authors.lastname: Lee
authors.forename: J-G
authors.initials: JG
authors.lastname: Park
authors.forename: D T
authors.initials: DT
authors.lastname: Adroja
authors.forename: D
authors.initials: D
authors.lastname: Khomskii
authors.forename: S
authors.initials: S
authors.lastname: Streltsov
authors.forename: K A
authors.initials: KA
authors.lastname: McEwen
authors.forename: H
authors.initials: H
authors.lastname: Sakai
authors.forename: K
authors.initials: K
authors.lastname: Yoshimura
authors.forename: V I
authors.initials: VI
authors.lastname: Anisimov
authors.forename: D
authors.initials: D
authors.lastname: Mori
authors.forename: R
authors.initials: R
authors.lastname: Kanno
authors.forename: R
authors.initials: R
authors.lastname: Ibberson