•Hilbert v. Löhneysen^{1,2}, Frank Obermair^{1},
Christian Pfleiderer^{1}, Almut Schröder^{3} und Oliver
Stockert^{4}
^{1}Physikalisches Institut, Universität Karlsruhe, 76128
Karlsruhe
^{2}FZK, Institut für Festkörperphysik, 76021 Karlsruhe
^{3}Department of Physics, Kent State University, Kent 44242,
USA
^{4}MPI für chemische Physik fester Stoffe, 01187 Dresden

The magnetic fluctuations at the onset of antiferromagnetism in CeCu_{6-x}Au_{x},
i.e. for x = 0.1, exhibit only critical slowing down'' set by temperature,
as expected for a quantum phase transition [1]. The E/T scaling observed
extends over the entire Brillouin zone and not only over the critical quasi-onedimensional
regions [2] in q space. Here E is the energy transfer observed by inelastic
neutron scattering. The anomalous scaling exponent a
» 0.75 is even observed in the T dependence
of the dc magnetization [3]. This has prompted models of quantum criticality
in heavy-fermion systems where the characteristic temperature scale below
which heavy fermions form out of itinerant electrons and f electrons, goes
to zero [1,4]. Here we show by means of resistivity and thermopower measurements
that the Kondo temperature remains finite, suggesting the existence of
another, yet hidden energy scale vanishing at the onset of antiferromagnetism
and thus giving rise to local criticality.

[1] A. Schröder et al., Nature **407**, 351 (2000)

[2] O. Stockert et al., Phys. Rev. Lett. **80**, 5627 (1998)

[3] A. Schröder et al., Phys. Rev. Lett. **80**, 5623 (1998)

[4] Q. Si et al., Nature **413**, 804 (2001)