Manuel Brando
MPI Chemical Physics of Solids
Abstract:
I will present a rare example of electronuclear quantum criticality in
a metal. The compound YbCu4.6Au0.4 is located at an unconventional
quantum critical point (QCP). In this material the
relevant Kondo and RKKY exchange interactions are very weak, of the
order of 1 K. Furthermore, there is a strong competition between
antiferromagnetic and ferromagnetic correlations, possibly due
to geometrical frustration within the fcc Yb sublattice. This causes
strong spin fluctuations which prevent the system to order
magnetically. Because of the very low Kondo temperature the Yb3+ 4f-
electrons couple weakly with the conduction electrons allowing the
coupling to the nuclear moments of the 171Yb and 173Yb isotopes to
become important. Thus, the quantum critical fluctuations
observed at the QCP derive not from purely electronic states but from
entangled electronuclear states. This is evidenced in the anomalous
temperature and field dependence of the specific heat at
low temperatures.