Echo of the Quantum Phase Transition of CeCu$_{6-x}$Au$_x$ in XPS: Breakdown of Kondo Screening

TL;DR

This study uses XPS to investigate how Kondo screening breaks down at the quantum phase transition in CeCu$_{6-x}$Au$_x$, revealing abrupt changes in electronic properties near the critical concentration.

Contribution

It provides the first XPS evidence of the breakdown of Kondo screening at the quantum critical point in CeCu$_{6-x}$Au$_x$, linking spectroscopic changes to quantum phase transition phenomena.

Findings

Abrupt change in $f$-occupation number $n_f$ at $x_c=0.1$

Sudden variation in core-hole potential $U_{df}$ at critical concentration

Results align with Anderson model predictions and previous UPS data

Abstract

We present an X-ray photoemission study of the heavy-fermion system CeCu$_{6-x}$Au$_x$ 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 of 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 UPS measurements %\cite{klein08qpt} and provide further information about the precursors of quantum criticality at elevated temperatures.