The important role of coherence for the heavy fermion state

Abstract

We investigated the influence of non-magnetic dopants on two heavy fermion systems and discovered a common behavior. When copper in CeCu 2Si 2 is substituted by up to 20% by metals like Pt, Ir, Os, or Ni, there is a reduction of the Sommerfeld parameter, γ, that is solely a function of the concentration. This decrease is thus independent of the special element. Furthermore, there is quantitatively the same rate-dependent γ decrease when cerium is partially substituted by Y or Lu. This means an equal behavior of the f-atom sublattice and the ligand sublattice. Recent measurements on another heavy fermion system, namely CePtSi, yield the same rate-dependent relative γ decrease (for Ni impurities on Pt sites) as in CeCu 2Si 2 and thus suggest a possible universal role of coherence for the forming of the heavy fermion ground state. Measurements of resistivity and magnetic susceptibility show how the lattice disturbances are reflected in the electronic transport and magnetic response. We especially try to elucidate to what extent electronic scattering and the coherence length affect the heavy fermion state.