Two Energy Scales and Slow Crossover in ${\mathrm{YbAl}}_3$

Experimental results for the susceptibility, magnetization, specific heat, $4f$ occupation number, Hall effect, and magnetoresistance for single crystals of the intermediate valence (IV) compound ${\mathrm{YbAl}}_3$ show that, in addition to the Kondo temperature scale $T_K\sim 670\mathrm{K}$, there is a low temperature scale $T_{\mathrm{coh}}\sim 30–40\mathrm{K}$ for the onset of Fermi liquid coherence. Furthermore, the crossover from the low temperature Fermi liquid regime to the high temperature local moment regime is slower than predicted by the Anderson impurity model. We suggest that these effects are generic for IV compounds and we discuss them in terms of the theory of the Anderson lattice.