Echo of the quantum phase transition of CeCu6-xAux in XPS: Breakdown of Kondo screening

We present an x-ray photoemission study of the heavy fermion system CeCu6-xAux across the magnetic quantum phase transition of this compound at temperatures above the single-ion Kondo temperature T-K. In dependence of the Au concentration x we observe a sudden change in the f-occupation number n(f) and the core-hole potential U-df at the critical concentration x(c)=0.1. We interpret these findings in the framework of the single-impurity Anderson model. Our results are in excellent agreement with findings from earlier ultraviolet photoemission spectroscopy measurements and provide further information about the precursors of quantum criticality at elevated temperatures.