Fermi volume evolution and crystal field excitations in heavy-fermion compounds probed by time-domain terahertz spectroscopy

TL;DR

This study uses time-domain terahertz spectroscopy to investigate how heavy-fermion bands and crystal field excitations evolve with temperature in CeCu6-xAux compounds, revealing the role of high-energy Kondo scales.

Contribution

It introduces a novel THz spectroscopy approach to distinguish heavy band and crystal field contributions and links their evolution to high-energy Kondo physics in heavy-fermion materials.

Findings

Heavy bands form via an exponentially enhanced high-energy Kondo scale.

Crystal-electric-field states influence the Kondo band formation.

Results support specific quantum critical scenarios.

Abstract

We measure the quasiparticle weight in the heavy-fermion compound CeCu$_{6-x}$Au$_{x}$ ($x=0,\ 0.1$) by time-resolved THz spectroscopy for temperatures from 2 up to 300\,K. This method distinguishes contributions from the heavy Kondo band and from the crystal-electric-field satellite bands by different THz response delay times. We find that the formation of heavy bands is controlled by an exponentially enhanced, high-energy Kondo scale once the crystal-electric-field states become thermally occupied. We corroborate these observations by temperature-dependent dynamical mean-field calculations for the multi-orbital Anderson lattice model and discuss consequences for quantum critical scenarios.