Inelastic neutron scattering study of crystalline electric field excitations in the caged compounds NdT2Zn20 (T = Co, Rh, and Ir)

We have measured crystalline electric field (CEF) excitations of Nd3+ ions in the two-channel Kondo lattice candidates NdT2Zn20 (T = Co, Rh, and Ir) by means of inelastic neutron scattering (INS). In the INS measurements at 5 K, dispersionless excitations were observed at 3.8 and 7.2 meV for T = Co, 3.1 and 5.8 meV for T = Rh, and 3.0 and 5.3 meV for T = Ir. Analyses of the temperature dependence of the INS spectra confirm that the CEF ground states are the Gamma 6 doublet, that is a requisite for manifestation of the magnetic two-channel Kondo effect. For T = Co, a shoulder was observed at 7.7 meV close to the CEF excitation peak centered at 7.2 meV. The shoulder is attributed to a bound state of the CEF and low-lying optical phonon excitations.