  We propose a new criterion for distinguishing the Hertz-Millis (HM) and the
local quantum critical (LQC) mechanism in heavy fermion systems with a magnetic
quantum phase transition (QPT). The criterion is based on our finding that the
spin screening of Kondo ions can be completely suppressed by the RKKY coupling
to the surrounding magnetic ions even without magnetic ordering and that,
consequently, the signature of this suppression can be observed in
spectroscopic measurements above the magnetic ordering temperature. We apply
the criterion to high-resolution photoemission (UPS) measurements on
CeCu$_{6-x}$Au$_{x}$ and conclude that the QPT in this system is dominated by
the LQC scenario.
