We present results of low-temperature calorimetric and resistive measurements on the isostructural heavy-fermion compounds CeCu 2 Si 2 and CeNi 2 Ge 2 . 'Non-Fermi-liquid' effects are established which suggest the nearness of an antiferromagnetic quantum critical point (QCP) in both systems. The observed deviations from the properties of a Landau Fermi liquid (FL) may be related to anomalous energy dependences of both the quasiparticle mass and the quasiparticlequasiparticle scattering cross section. For CeNi 2 Ge 2 , a moderately heavy FL can be recovered by application of moderate values of either magnetic field or hydrostatic pressure. For p = 1.7 GPa a novel, non-superconducting, phase transition has been discovered at T 1 1 K.

No abstract

No abstract

The interplay between superconductivity and magnetism in CeCu 2 Si 2 has been investigated by means of microprobe, muon spin rotation and relaxation (SR͒, and specific-heat measurements on four slightly offstoichiometric polycrystalline samples Ce 1ϩx Cu 2ϩy Si 2 . Microprobe analysis reveals that within the errors (Ϯ3%) the main phases of all four samples exhibit the ideal stoichiometry 1:2:2 and their relative composition varies by less than 2%. Muon spin rotation and relaxation measurements, however, reveal pronounced differences in their ground states. The nonsuperconducting sample Ce 0.99 Cu 2.02 Si 2 exhibits a phase transition at T m ϭ0.67 K to a magnetically ordered ground state of unknown structure, with a lower limit on the size of the frozen moments Ϸ0.2 B . For TϽT m slow residual fluctuations of these moments at a rate Ϸ3 MHz are observed. In the three superconducting samples comparable magnetic behavior is found in reduced volume fractions. Paramagnetic and magnetic regions are distributed inhomogeneously in these samples, the relative volume fractions being strongly sample and temperature dependent. In all samples considerable volume fractions remain magnetic down to Tϭ60 mK. The present data provide evidence that superconductivity sets in first in the paramagnetic regions, and, on further cooling, reduces the magnetically ordered volume fraction. Superconductivity and magnetic order do not appear to spatially coexist, but compete in CeCu 2 Si 2 .

No abstract