Crystal field studies on the heavy fermion compound CeNi8CuGe4

Substitution of nickel by copper in the heavy fermion system CeNi9-xCuxGe4 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.