Local Structural Evidence for Strong Electronic Correlations in LiRh${}_2$O${}_4$ Spinel

Abstract

The local structure of the spinel LiRh${}_2$O${}_4$ has been studied using atomic pair distribution function (PDF) analysis of powder x-ray diffraction data. This measurement is sensitive to the presence of short Rh-Rh bonds that form due to dimerization of Rh${}^{4+}$ ions on the pyrochlore sublattice, independent of the existence of long range order. We show that structural dimers exist in the low-temperature phase, as previously supposed, with a bond shortening of $\Delta r\sim 0.15$ Å. The dimers persist up to 350 K, well above the insulator-metal transition, with $\Delta r$ decreasing in magnitude on warming. Such behavior is inconsistent with the Fermi surface nesting-driven Peierls transition model. Instead, we argue that LiRh${}_2$O${}_4$ should properly be described as a strongly correlated system.

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• Valence bond crystal in a pyrochlore antiferromagnet with orbital degeneracy
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