Quantum fluctuations and the magnetic ground state of Ce3Pd20Si6

The temperature and magnetic field dependence of neutron-scattering studies on the heavy fermion compound Ce3Pd20Si6 are reported. Inelastic neutron scattering reveals two crystal-field excitations corresponding to the environments of the two distinct rare-earth locations within this cubic compound. Surprisingly, the ground states of the two individual Ce sites are inequivalent with the 4a site having a Gamma(7) ground state, while the 8c site reveals a Gamma(8) ground state. This is in contrast to the situation found in the analogous compound Ce3Pd20Ge6, where the Gamma(8) ground state is realized for both Ce sites. In addition, these results reveal an interaction between the 8c and 4a sites previously believed to be absent. The ground state was probed with uniaxial polarization analysis across the region in which field-induced quantum criticality has previously been determined. In zero applied magnetic field no long-range magnetic order could be determined. However, further evidence of field-induced quantum criticality is presented with the observation of diffuse scattering consistent with quantum fluctuations due to nearest-neighbor spin correlations between the two Ce sites.