NON-FERMI-LIQUID BEHAVIOR IN STRONGLY CORRELATED ELECTRON-SYSTEMS

Non-Fermi-liquid (NFL) behavior in three-dimensional metals with stron g electron correlations can have different origins, viz. collective or single-ion effects. The former is manifest at a magnetic instability where the system changes from a nonmagnetic to a magnetic ground state as a function of some parameter like concentration or pressure. We re view the properties of the exemplary NFL heavy-fermion system CeCu6-xA ux at this magnetic instability, i.e. a logarithmic divergence of the specific-heat coefficient gamma(T)= C/T, a cusp in the magnetic DC sus ceptibility chi(T) for T --> 0, and a T-linear contribution Delta rho to the electrical resistivity, as opposed to the Fermi-liquid behavior gamma similar to chi approximate to const, Delta rho similar to T-2 f ound in many heavy-fermion systems, including the parent compound CeCu 6. Single-ion effects leading to NFL behavior are overscreening of mag netic or quadrupolar degrees of freedom of a magnetic impurity or a di stribution of Kondo temperatures in a disordered alloy. Similarities a nd differences of the NFL phenomenology between these scenarios will b e reviewed.