Well-Defined Crystal Field Splitting Schemes and Non-Kramers Doublet Ground States of f Electrons in PrT2Zn20 (T = Ir, Rh, and Ru)

Inelastic neutron scattering studies of Pr\(T_{2}\)Zn20 (\(T\) = Ir, Rh, and Ru) were carried out in order to reveal \(f\) electron states indispensable for the low-temperature properties of Pr\(T_{2}\)Zn20 associated with multipole degrees of freedom. Sharp excitation peaks, which are located within excitation energies of less than 10 meV, are attributed to crystal field splitting level schemes of \(4f^{2}\) in Pr3+ ions. Data of the Ir-based compound is explained by a non-Kramers doublet ground state in the local symmetry \(T_{d}\) for this system. Results of the Rh-based compound are explained by the scheme for the Pr-site local cubic symmetry \(T\) in the low-temperature structural phase, which is lower than \(T_{d}\). In the Ru-based compound, the doublet is split as a result of the loss of local cubic symmetry through structural transformation. These experimental results confirm the non-Kramers doublet ground state that causes the quadrupole ordering or orbital Kondo effect predicted for this series...