title: Band Jahn-Teller instability and formation of valence bond solid in a mixed-valent spinel oxide LiRh2O4.
abstract: We have synthesized a new spinel oxide LiRh2O4 with a mixed-valent configuration of Rh3+ and Rh4+. At room temperature, it is a paramagnetic metal, but on cooling, a metal-insulator transition occurs and a valence bond solid state is formed below 170 K. We argue that the formation of valence bond solid is promoted by a band Jahn-Teller transition at 230 K and the resultant confinement of t_{2g} holes within the xy band. The band Jahn-Teller instability is also responsible for the observed enhanced thermoelectric power in the orbital-disordered phase above 230 K.
authors.affiliation: RIKEN (The Institute of Physical and Chemical Research), Hirosawa 2-1, Wako 351-0198, Japan.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Seiji
authors.initials: S
authors.lastname: Niitaka
authors.forename: Masaya
authors.initials: M
authors.lastname: Uchida
authors.forename: Takeshi
authors.initials: T
authors.lastname: Waki
authors.forename: Masashi
authors.initials: M
authors.lastname: Takigawa
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Nakatsu
authors.forename: Akira
authors.initials: A
authors.lastname: Sekiyama
authors.forename: Shigemasa
authors.initials: S
authors.lastname: Suga
authors.forename: Ryotaro
authors.initials: R
authors.lastname: Arita
authors.forename: Hidenori
authors.initials: H
authors.lastname: Takagi