title: Variety of valence bond states formed of frustrated spins on triangular lattices based on a two-level system Pd(dmit)2.
abstract: Recent studies on the physical properties of the triangular system based on the Pd(dmit)2salts (dmit=1,3-dithiole-2-thione-4,5-dithiolate) are reviewed. Quantum chemical architectures of the Pd(dmit)2molecule and its dimer are introduced with emphasis on the strong dimerization of a two-level system, which provides unique physical properties of the salts. The magnetic properties are outlined in view of the magneto-structural correlation specific to the frustrated spin systems. Some newly discovered ground states and their origins are discussed, for which the valence bond formation plays a key role. Among them, the two-level structure is crucial for the novel charge-separated state found in two salts. The valence bond ordering, similar to the spin-Peierls transition, has been found in a two-dimensional frustrated spin system. The physical aspects and possible relation to the pressure-induced superconductivity are discussed.
authors.affiliation: Department of Physics, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Tamura
authors.affiliation: Condensed Molecular Materials Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Reizo
authors.initials: R
authors.lastname: Kato
keywords: HOMO-LUMO interplay; Pd(dmit)2 salts; antiferromagnets; frustration; spin gap; superconductivity; triangular lattice