The low-temperature phase of Rh- and Ce-doped PrRu4P12 was investigated by inelastic neutron scattering, magnetic susceptibility and x-ray superlattice reflection measurement. Inelastic neutron scattering experiments have revealed that 4f electron states in both compounds change drastically from two distinct states with staggered alignment in multipole ordering phase into nearly equivalent states at around 20 K with lowering temperature. X-ray superlattice reflections in both compounds decrease rapidly below 20 K, which corresponds to the reduced resistivity in same temperature range. The saturation in magnetic susceptibility at low temperatures suggests that all the 4f-electron ground states are singlet for both compounds, in contrast to the two staggered ground states in the ordering phase of PrRu4P12. These results on low temperature phase in both Rh- and Ce-doped compounds may derive from electron doping effect.
