Exotic behaviours in the Pr-based filled skutterudites

The exotic features of the Pr-based filled skutterudites are reviewed based on the electronic transport properties, specific heat and de Haas-van Alphen experiments, putting the emphasis on PrFe4P12 and PrOs4Sb12. As references, the experiments on the related La- and Ce-filled skutterudites are also examined and discussed. Compared to their La reference compounds, the Fermi surface is very similar in PrOs4Sb12, suggesting the well localized character of 4f electrons, while it looks largely different in PrFe4P12. For the cyclotron effective mass, both PrFe4P12 and PrOS4Sb12 exhibit a strong enhancement, in reasonable agreement with the large specific heat coefficient.