Anomalous temperature dependence of the electrical resistivity in R$_3$Co$_4$Ge$_{13}$ (R = Y, Lu) single crystals

TL;DR

This study investigates the unusual temperature dependence of electrical resistivity in R$_3$Co$_4$Ge$_{13}$ single crystals, revealing semiconducting-like behavior caused by structural disorder and proposing a combined conduction model.

Contribution

It demonstrates that the resistivity behavior cannot be explained by traditional models but can be understood through a parallel conduction framework considering disorder effects.

Findings

Resistivity shows semiconducting-like behavior despite metallic composition.

Neither Arrhenius nor VRH models fit the resistivity data across 2-350 K.

A combined conduction model explains the temperature dependence effectively.

Abstract

The presence of strong disorder can significantly impact electrical conduction in metallic systems. Here, we investigate the temperature dependence of the electrical resistivity, $\rho(T)$, in nonmagnetic single crystals of the Remeika-phase cage compounds R$_3$Co$_4$Ge$_{13}$ (R = Y, Lu). Contrary to the density of states (DOS) calculations in the literature, the experimentally measured $\rho(T)$ in both compounds exhibits semiconducting-like behavior, which we attribute to the strong structural disorder due to its unique crystal structure and low carrier-density. A detailed analysis of the electrical resistivity data reveals that neither the Arrhenius thermal activation law nor variable-range hopping (VRH) models can adequately describe their temperature dependence over the broad temperature range of 2-350 K. However, a model incorporating parallel conduction through both semiconducting and metallic channels provides an adequate explanation. In addition to a dominant metallic conduction below $\sim 10$~K, a negative temperature coefficient of the electrical resistivity ($d\rho/dT$) is found in both samples. In the absence of magnetic impurities, the observed $d\rho/dT < 0$ is interpreted in terms of the structural Kondo mechanism.