Band Jahn-Teller Instability and Formation of Valence Bond Solid in a Mixed-Valent Spinel Oxide LiRh2O4

TL;DR

This study reports the synthesis of LiRh2O4, a mixed-valent spinel oxide, which undergoes a metal-insulator transition and forms a valence bond solid driven by band Jahn-Teller instability, with implications for thermoelectric properties.

Contribution

It reveals the role of band Jahn-Teller instability in valence bond solid formation in a new mixed-valent spinel oxide.

Findings

LiRh2O4 is a paramagnetic metal at room temperature.

A metal-insulator transition occurs below 170 K.

Enhanced thermoelectric power observed above 230 K.

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 t2g 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.