Low-temperature thermal conductivity and thermopower of CeCu_6-xAu_x near the magnetic quantum phase transition

The thermal conductivity κ and thermopower S in the heavy-fermion alloy CeCu_6-xAu_x at the critical concentration x = 0.1 separating magnetically ordered and non-magnetic ground states, has been measured in the range 0.1-2.5 K at zero magnetic field and B = 6 T. k(T) is found to be linear at high T in close agreement with pure CeCu₆. In the limit of low T, κ is strongly suppressed. In contrast to x = 0, for x = 0.1κ increases only very weakly in a magnetic field of 6 T. The (positive) thermopower is enhanced with respect to x = 0, dropping off only well below 0.5 K. The magnetic field reduces strongly the value of S and leads to a collapse of S(T) for x = 0 and 0.1 onto identical curves.