The ground state of PrFe₄P₁₂ probed by thermal and thermoelectric transport

Among the Pr-filled Skutterudites, PrFe₄P₁₂ is distinguished by the presence of an unidentified phase transition at T _A=6.5 K. Here we report on a study of the effect of this phase transition on thermal and thermoelectric transport. The lattice thermal conductivity drastically increases with the ordering, as a consequence of a large drop in carrier concentration and a strong electron-phonon coupling. The low level of carrier density in the ordered state is confirmed by the anomalously large values of the Seebeck and Nernst coefficients. Our results document a radical reconstruction of the Fermi surface, which leads to the emergence of a heavy-electron semi-metal below TA.