Anomalous ordered phase in 4f2-based heavy electron PrFe4P12 Original Research Article

Recent study on the anomalous ordered state (ODS) in filled-skutterudite PrFe4P12 is presented, where the existence of a rare 4f2-based heavy electron (HE) state outside ODS has been experimentally confirmed recently. From specific heat measurements, it is found that the HE behavior is largely suppressed in ODS. The Pr nuclear Schottky contribution strongly indicates that ODS is non-magnetic, most probably of quadrupolar origin. We argue that the quadrupolar degree of freedom on the Pr-ions may play an essential role in the heavy quasiparticle band formation in PrFe4P12. We also report the La-substitution effect on ODS.