Slow crossover in YbXCu4 (X = AgCd, In, Mg, Tl, Zn) intermediate-valence compounds - art. no. 054427

We compare the results of measurements of the magnetic susceptibility chi ( T), the linear coefficient of specific heat gamma (T) = C(T)/T, and 4f occu pation number n(f)(T) for the intermediate-valence compounds YbXCu4 (X = Ag , Cd, In, Mg, Tl, Zn) to the predictions of the Anderson impurity model, ca lculated in the noncrossing approximation (NCA). The crossover from the low temperature Fermi-liquid state to the high-temperature local-moment state is substantially slower in the compounds than predicted by the NCA; this co rresponds to the "protracted screening" recently predicted for the Anderson lattice. We present results for the dynamic susceptibility, measured throu gh neutron-scattering experiments, to show that the deviations between theo ry and experiment are not due to crystal-field effects, and we present x-ra y-absorption finestructure results that show the local crystal structure ar ound the X atoms is well ordered, so that the deviations probably do not ar ise from Kondo disorder. The deviations may correlate with the background c onduction electron density, as predicted for protracted screening.