Origin of the pressure dependence of the Kondo temperature in Ce- and Yb-based heavy-fermion compounds

We find that the unusual pressure dependence of the Kondo temperature in Yb-based heavy-fermion (HF) compounds can be explained by the competition between two mechanisms of coupling between f electrons and the lattice. An increase of the hybridization between f and conduction electron states under pressure results in the increase of the Kondo temperature while the suppression of valency fluctuations of rare-earth ions under pressure leads to the decrease of the Kondo temperature. In contrast to Yb compounds, in Ce compounds pressure enhances both the hybridization and valency fluctuations. As a result the Kondo temperature increases. We compare the theory with available experimental data and find a qualitative and quantitative agreement.