Evolution of the Kondo lattice and non-Fermi liquid excitations in a heavy-fermion metal

TL;DR

This study investigates how Kondo lattice coherence in a heavy-fermion metal evolves into non-Fermi liquid excitations near a quantum critical point, revealing the microscopic origin of strange-metal behavior.

Contribution

It provides direct experimental evidence of the development and breakdown of Kondo lattice coherence leading to non-Fermi liquid states in a prototypical heavy-fermion metal.

Findings

Kondo lattice peak emerges below 25 K with non-trivial temperature dependence.

Peak width minimized in the quantum critical regime at low temperatures.

Results demonstrate non-Fermi liquid excitations in quantum critical metals.

Abstract

Strong electron correlations can give rise to extraordinary properties of metals with renormalized quasiparticles which are at the basis of Landau's Fermi liquid theory. Near a quantum critical point, these quasiparticles can be destroyed and non-Fermi liquid behavior ensues. YbRh$_2$Si$_2$ is a prototypical correlated metal as it exhibits quasiparticles formation, formation of Kondo lattice coherence and quasiparticle destruction at a field-induced quantum critical point. Here we show how, upon lowering the temperature, the Kondo lattice coherence develops and finally gives way to non-Fermi liquid electronic excitations. By measuring the single-particle excitations through scanning tunneling spectroscopy down to 0.3 K, we find the Kondo lattice peak emerging below the Kondo temperature $T_{\rm K} \sim$ 25 K, yet this peak displays a non-trivial temperature dependence with a strong increase around 3.3 K. At the lowest temperature and as a function of an external magnetic field, the width of this peak is minimized in the quantum critical regime. Our results provide a striking demonstration of the non-Fermi liquid electronic excitations in quantum critical metals, thereby elucidating the strange-metal phenomena that have been ubiquitously observed in strongly correlated electron materials.