Crystal field studies on the heavy fermion compound CeNi₈CuGe₄

Substitution of nickel by copper in the heavy fermion system CeNi_9−xCu_xGe₄ alters the local crystal field environment of the Ce³⁺-ions. This leads to a quantum phase transition near x ≈ 0.4, which is not only driven by the competition between Kondo effect and RKKY interaction, but also by a reduction of an effectively fourfold to a twofold degenerate crystal field ground state. To study the consequences of a changing crystal field in CeNi₈CuGe₄ on its Kondo properties, inelastic neutron scattering (INS) experiments were performed. Two well-defined crystal field transitions were observed in the energy-loss spectra at 4K. The crystal field level scheme determined by neutron spectroscopy is compared with results from specific heat measurements.