Strongly-disordered hybridization and non-Fermi liquid behavior in CePt$_4$Ge$_{12-x}$Sb$_x$ studied with thermoelectric power

Non-Fermi liquid (NFL) behavior is commonly associated with the presence of a nearby quantum critical point, but can also be observed in other scenarios. In a clean system, hybridization between localized and itinerant electron states can be characterized by a single Kondo temperature $T_K$, but introducing chemical disorder can lead to a wide distribution of $T_K$ values. Given sufficient disorder, the resulting distribution will tend to include an appreciable number of localized electron states which are characterized by $T_K \sim$ 0 K, and NFL behavior emerges. A Kondo-disorder type of NFL behavior was recently reported in the filled skutterudite system CePt$_4$Ge$_{12-x}$Sb$_x$ in the vicinity of $x = 1$. We performed a study of the thermoelectric power $S(T)$ for this system and observed an evolution of $S(T)$ with $x$ that is dramatic and broadly consistent with the boundaries of the proposed phase diagram. The effect of disordered hybridization is clearly observed in a low-temperature feature in $S(T)$ in the range $0.5 \le x \le 1.5$ and NFL behavior is also observed at x = 1. These results clearly demonstrate how sensitively $S(T)$ is able to probe a Kondo disorder system.