Anomalous Pressure Dependence of Kadowaki-Woods ratio and Crystal Field Effects in Mixed-valence YbInCu$_4$

The Mixed-valence (MV) compound YbInCu$_{4}$ was investigated by electrical resistivity at low temperatures and high pressures. Scaling of the first derivative of the resistivity at different pressures reveals two characteristic temperatures, where the slope in $d\rho /dT$ changes abruptly: $T_{v}$ due to the first-order MV transition and $T_{CEF}$ due to crystal-field effects. The Kadowaki-Woods (KW) ratio, $A/\gamma ^{2}$, is anomalously small at $P=0$, but sharply increases to a value comparable to that of heavy fermion compounds at $P=25$~kbar. The dramatic pressure dependence is attributed to a change in the ground state degeneracy from an octet to a doublet at $P\approx 25$~kbar. [1] K. Kadowaki and S. B. Woods, Solid State Commun. 58, 507 (1986), [2] T. Park et al., cond-mat/0409243 (2004).