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 $14Å$⁠) of the charge carriers in $CeCu6$⁠. For the compound $CeCu5.9Au0.1$⁠, corresponding to the QCP, one observes correlated power-law behavior of the temperature dependence of the Hall coefficient $RH(T)∼T−0.4$ and magnetic susceptibility $χ(T)∼T−0.4$⁠, as is characteristic of the regime of quantum critical behavior. For compounds in the immediate vicinity of the QCP an anomalous, even contribution $RH2$ to the angular dependence of the Hall voltage appears at temperatures below $T*∼24K$ and becomes stronger with increasing magnetic field. Different scenarios for passage through the QCP and their applicability for describing the Hall-effect anomalies in the substitutional solid solutions $CeCu6−xAux$ are discussed.