Strongly correlated electron phenomena in Pr-based filled skutterudite compounds

Recent experiments on the Pr-based filled skutterudite arsenides and antimonides PrOs4Sb12PrOs4Sb12, Pr(Os1-xRux)4Sb12Pr(Os1-xRux)4Sb12, Pr1-xNdxOs4Sb12Pr1-xNdxOs4Sb12, PrFe4As12PrFe4As12, PrRu4As12PrRu4As12, and PrOs4As12PrOs4As12 are reviewed. The heavy fermion compound PrOs4Sb12PrOs4Sb12 exhibits unconventional strong-coupling superconductivity below Tc=1.85K that breaks time reversal symmetry, apparently consists of several distinct superconducting phases, and may involve triplet spin pairing of electrons. Studies of the alloy systems Pr(Os1-xRux)4Sb12Pr(Os1-xRux)4Sb12 and Pr1-xNdxOs4Sb12Pr1-xNdxOs4Sb12 revealed rich T–x   phase diagrams and a strong suppression of the high field ordered phase and the unconventional superconductivity of PrOs4Sb12PrOs4Sb12 with Ru substitution. Among the three Pr-based filled skutterudite arsenides, PrFe4As12PrFe4As12 has a ferromagnetic ground state, PrRu4As12PrRu4As12 exhibits conventional BCS superconductivity, and PrOs4As12PrOs4As12 is an antiferromagnet.