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

Abstract

The presence of strong disorder can significantly impact electrical conduction in metallic systems. Here, we investigate the temperature dependence of the electrical resistivity, $ρ(T)$, 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 $ρ(T)$ 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 ($dρ/dT$) is found in both samples. In the absence of magnetic impurities, the observed $dρ/dT < 0$ is interpreted in terms of the structural Kondo mechanism.

Figures (6)

• Figure 1: (a) SEM image of an Y$_3$Co$_4$Ge$_{13}$ crystal. The white rectangle indicates the selected area for the EDX map. Individual elemental analysis for (b) Y, (c) Co, and (d) Ge.
• Figure 2: Rietveld plot of the room temperature powder XRD pattern for (a) Y$_3$Co$_4$Ge$_{13}$ and (b) Lu$_3$Co$_4$Ge$_{13}$. The black crosses indicate the observed pattern, while the red line represents the calculated one. The gray line at the bottom displays the difference between the experimental and calculated patterns. The blue and pink vertical bars stand for the Bragg reflections. (c) The crystal structure for R$_3$Co$_4$Ge$_{13}$ series in the Pm$\overline{3}$n space group.
• Figure 3: Temperature dependence of the electrical resistivity for (a) Y$_3$Co$_4$Ge$_{13}$ and (b) Lu$_3$Co$_4$Ge$_{13}$.
• Figure 4: Temperature dependence of the electrical resistivity for Y$_3$Co$_4$Ge$_{13}$ and Lu$_3$Co$_4$Ge$_{13}$. (a) and (b) shows the resistivity as a function of $1/T$, the insets show Arrhenius fit. (c) and (d) The resistivity as a function of $T^{-1/4}$ with VRH model. (e) and (f) The resistivity as a function of $T^{-1/2}$ with Efros-Shlovskii model.
• Figure 5: Temperature dependence of the electrical resistivity of (a) Y$_3$Co$_4$Ge$_{13}$ and (b) Lu$_3$Co$_4$Ge$_{13}$. Solid lines represent the fitting of Eq. \ref{['eq:rho']}, the dashed line (blue) is the simulated semiconductor channel with Eq. \ref{['sigma_m']}, and the dotted line (green) is simulated with Eq. \ref{['sigma_s']} the metallic channel.