Electronic correlations and non-Fermi-liquid behaviour in ACu3Ru4O12-perovskites

Among the large variety of AC3B4O12-type perovskites, the copper-ruthenates (C=Cu, B=Ru) form a subclass exhibiting strongly correlated electron behaviour. A special feature of these compounds is that the ideal stoichiometry and structure is preserved for a large number of different A-site cations with different valence states. We have systematically studied the electronic properties by specific heat, magnetic susceptibility, transport, NMR/NQR and neutron scattering experiments. The compound A=Ca is a correlated metal showing non-Fermi-liquid behaviour below 2 K, as indicated by a logarithmic increase of the specific heat and deviations from a Korringa behaviour of the spin lattice relaxation rate. In the case of A=Pr, an anomaly in the specific heat occurs at 0.5 K whose maximum shifts to higher temperatures with increasing magnetic field. Along with data acquired from inelastic neutron scattering we obtain strong indications for a pronounced crystal field splitting.