Anomalous pressure dependence of the Kadowaki-Woods ratio and crystal-field effects in mixed-valence YbInCu4

The mixed-valence compound YbInCu4 was investigated by electrical resistivity and ac specific heat at low temperatures and high pressures. At atmospheric pressure, its Kadowaki-Woods (KW) ratio A/γ2 is 16 times smaller than the universal value RKW(=1.0×10- 5μΩ•cm•mol2•K2•mJ-2), but sharply increases to 16.5RKW at 27 kbar. The pressure-induced change in the KW ratio and deviation from RKW are analyzed in terms of the change in f-orbital degeneracy N and carrier density n. This analysis is further supported by a dramatic change in residual resistivity ρ0 near 25 kbar, where ρ0 jumps by a factor of 7.