Hall-effect anomalies near the quantum critical point in CeCu6−xAux

The results of Hall-effect and resistance measurements on the substitutional solid solutions CeCu6−xAux with concentrations 0⩽x⩽0.3, corresponding to a wide neighborhood of the quantum critical point (QCP) at x=0.1, are presented. The measurements are made by rotation of the sample in a constant magnetic field of up to 70kOe in a temperature interval of 1.8–300K. For the classic heavy-fermion compound CeCu6 the temperature dependence of the Hall coefficient RH(T) exhibits a complex activational form with activation energies Ea1∕kB≈110K and Ea2∕kB≈1.5K in the temperature intervals 50–300K and 3–10K, respectively. It is shown that the anomalous behavior of the Hall effect can be explained in a spin-polaron approach, in which the values Ea1,2 can be associated to the binding energy of many-body and one can obtain estimates of the effective mass (meff1,2≈130–150m0) and localization radius (ap1,2*≈1.7 and 14A) of the charge carriers in CeCu6. For the compound CeCu5.9Au0.1, corresponding to the QCP, one observe...