Anomalous Behaviors in Transport Properties of CeCu₆ and CeCu_5.9Au_0.1

Abstract

We have investigated the thermoelectric power (TEP) and Hall coefficient (R_H), along with the field dependence of Hall resistivity (ρ_H) and magnetoresistance (MR) in single crystals of CeCu_5.9Au_0.1 and CeCu₆. In both compounds, R_H is highly anisotropic with respect to the field direction below ∼10 K. For H||[001], a negative minimum in ρ_H and a positive MR peak grow at low temperatures near 1.7 T, where a metamagnetic-like anomaly was reported for CeCu₆. The Au substitution induces drastic changes in R_H depending on the magnetic field direction, which is discussed in correlation with the predicted change in the Fermi surface across the quantum critical point. In CeCu_5.9Au_0.1, an unexpectedly large positive MR has been found at low temperatures and in low fields; its origin is discussed in comparison with the Hall resistivity. For all the principal axes, the Au-substitution effect on TEP is minor in both magnitude and anisotropy down to ∼1.5 K, suggesting no essential change in the electronic structure in the energy region above a few K.