Signature of quantum criticality in photoemission spectroscopy at elevated temperature

Abstract

A quantum phase transition (QPT) in a heavy-fermion (HF) compound may destroy the Fermi liquid groundstate. However, the conditions for this breakdown have remained obscure. We report the first direct investigation of heavy quasiparticle formation and breakdown in the canonical system CeCu${}_{6-x}$Au${}_x$ by ultraviolet photoemission spectroscopy at elevated temperatures without the complications of lattice coherence. Surprisingly, the single-ion Kondo energy scale $T_K$ exhibits an abrupt step near the quantum critical Au concentration of $x_c=0.1$. We show theoretically that this step is expected from a highly non-linear renormalization of the local spin coupling at each Ce site, induced by spin fluctuations on neighboring sites. It provides a general high-temperature indicator for HF quasiparticle breakdown at a QPT.

Published version, PRL, minor changes in wording

References in corpus (3)

• Fermi-liquid instabilities at magnetic quantum phase transitions
• Quantum Criticality in Heavy Fermion Metals
• High Resolution Photoemission Study on Low-T_K Ce Systems: Kondo Resonance, Crystal Field Structures, and their Temperature Dependence

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• Kondo Destruction in RKKY-Coupled Kondo Lattice and Multi-Impurity Systems
• Zooming in on heavy fermions in Kondo lattice models
• Nonlocal Kondo effect and quantum critical phase in heavy fermion metals
• Kondo breakdown in a spin-1/2 chain of adatoms on a Dirac semimetal
• Echo of the Quantum Phase Transition of CeCu${}_{6-x}$Au${}_x$ in XPS: Breakdown of Kondo Screening
• Kondo screening and beyond: an x-ray absorption and dichroism study of CePt${}_5$/Pt(111)
• Missing spectral weight in a heavy-fermion system far above Néel temperature