Non-Fermi liquid behavior in the filled skutterudite compound CeRu$_{4}$As$_{12}$

The filled skutterudite compounds of the form MT$_4$X$_{12}$ (M = alkali metal, alkaline earth, lanthanide, actinide, T = Fe, Ru, Os and X = P, As, Sb) exhibit a wealth of strongly correlated electron phenomena. The CeT$_4$X$_{12}$ subclass is interesting since it includes the only filled skutterudite known to show non - Fermi liquid (NFL) behavior, CeRu$_4$AS$_{12}$, in addition to various semiconductors where the gap size is correlated with the lattice constant. We present electrical resistivity $\rho$, specific heat C, and magnetic susceptibility $\chi$ measurements for the new compound, CeRu$_4$As$_{12}$, which reveal NFL T - dependences at low T, i.e., $\rho$(T) $\sim$ T$^{1.4}$ and weak power law or logarithmic divergences in C(T)/T and $\chi$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that in other Ce systems. The NFL behavior appears to be associated with a nonmagnetic or weakly magnetic ground state, as revealed by magnetization M(H,T) measurements.