Crystal field excitations in PrFe₄Sb₁₂ synthesized under high pressure

In the filled skutterudite PrFe₄Sb₁₂ with high Pr-site filling fraction synthesized under high pressure, the bulk properties indicate a singlet ground state of the crystal field (CF) and no phase transition at low temperature, in contrast to the reported magnetic ordering in the samples with relatively low filling fraction. In order to clarify the CF states in PrFe₄Sb₁₂ microscopically, we have performed the inelastic neutron scattering experiment on the PrFe₄Sb₁₂ synthesized under high pressure. The CF level scheme obtained from the results is Γ₁ (0 meV) - Γ⁽²⁾₄ (2.3 meV) - Γ⁽¹⁾₄ (11.4 meV) - Γ₂₃ (18 meV). Furthermore, it is found that the singlet-triplet states in low energy region have large off-diagonal matrix elements of quadrupoles, indicating the similarity of the CF states in the heavy fermion superconductor PrOs ₄Sb₁₂.