Jingwen Li, Debankit Priyadarshi, Chia-Jung Yang, Ulli Pohl, Oliver Stockert, Hilbert von Löhneysen, Shovon Pal, Manfred Fiebig, Johann Kroha:
Phys. Rev. B 111, 035117 (2025)
🔓 arXiv:2408.07345 (2024)
The competition between the Kondo spin-screening effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in heavy-fermion systems drives the quantum phase transition (QPT) between the magnetically ordered and the heavy-Fermi-liquid ground states. Despite intensive investigations of heavy quasiparticles on the Kondo-screened side of the QPT and of their breakdown at the quantum critical point, the magnetically ordering side has not systematically been studied. Using terahertz time-domain spectroscopy, we report a suppression of the Kondo quasiparticle weight in CeCu6−𝑥Au𝑥 samples on the antiferromagnetic (AFM) side of the QPT at temperatures as much as two orders of magnitude above the Néel temperature 𝑇N. With our systematic investigations into the high-temperature, paramagnetic region on the AFM side of the phase diagram of CeCu6−𝑥Au𝑥, i.e., with 𝑥=0.2, 0.3, and 0.5, we show that the suppression results from a quantum frustration effect induced by the temperature-independent RKKY interaction. Hence, our results emphasize that, in addition to critical fluctuations, the RKKY interaction may play an important role in the quantum-critical scenario.