•Hilbert v. Löhneysen^1,2, Frank Obermair¹, Christian Pfleiderer¹, Almut Schröder³ und Oliver Stockert^4
1Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe
²FZK, Institut für Festkörperphysik, 76021 Karlsruhe
³Department of Physics, Kent State University, Kent 44242, USA
⁴MPI für chemische Physik fester Stoffe, 01187 Dresden

The magnetic fluctuations at the onset of antiferromagnetism in CeCu_6-xAu_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)