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

TL;DR

This study reveals persistent Rh-Rh dimers in LiRh$_2$O$_4$ up to high temperatures, indicating strong electronic correlations rather than a Peierls transition, challenging conventional models of its phase change.

Contribution

The paper provides direct local structural evidence of Rh-Rh dimers in LiRh$_2$O$_4$, demonstrating their persistence above the insulator-metal transition, highlighting strong correlations.

Findings

Rh-Rh dimers exist in low-temperature phase

Dimers persist up to 350 K, above transition

Behavior inconsistent with Peierls transition model

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 $\Delta r \sim 0.15$ \AA . 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.