Probing the unconventional superconductivity of PrPt$_4$Ge$_{12}$ through Ce substitution*

Superconductivity has been observed in a new class of filled skutterudite compounds of the form $M$Pt$_{4}$Ge$_{12}$ ($M$ = Sr, Ba, La, Pr, and Th), with the Pr member exhibiting a high superconducting transition temperature $T_c$ $\sim$ 7.9 K. Most of these skutterudite compounds seems to exhibit conventional BCS-type superconductivity; however, superconductivity in Pr appears to be unconventional as it exhibits characteristics of time-reversal symmetry breaking. To help clarify the nature of the superconductivity in PrPt$_4$Ge$_{12}$, we studied the response of superconductivity to the substitution of Ce for Pr throughout the series Pr$_{1-x}$Ce$_x$Pt$_4$Ge$_{12}$ (0 $\leq$ x $\leq$ 1). Measurements of electrical resistivity, magnetic susceptibility, and specific heat were performed and superconductivity were observed up to a Ce concentration of 50$\%$. A pronounced change was observed in the temperature dependence of specific heat below $T_c$ where PrPt$_4$Ge$_{12}$ exhibits a crossover from a $T^3$ to an exponential temperature dependence when Ce is introduced.