Thermoelectric Power of the YbT${}_2$Zn${}_{20}$ (T = Fe, Ru, Os, Ir, Rh, and Co) Heavy Fermions

The thermoelectric power, $S(T)$, of the heavy fermions YbT${}_2$Zn${}_{20}$ ($T$ = Fe, Ru, Os, Ir, Rh, and Co) has been measured to characterize their strong electronic correlations. A large, negative, local minimum in $S(T)$ with approximately -70 $\mu$V/K is found for all compounds. From the observed local minimum, the energy scales associated with both the Kondo temperature and the crystalline electric field splitting are deduced and compared to previous specific heat measurements. At low temperatures, $S(T)$ follows a linear temperature dependence, $S(T)$ = $\alpha T$, with an enhanced value of $\alpha$ which is characteristic for a heavy fermion state. In the zero temperature limit, the enhanced $\alpha$ value strongly correlates with the electronic specific heat coefficient, $C(T)\mathrm{/}T$, due to the large density of states at the Fermi level.