Visualizing heavy fermions emerging in a quantum critical Kondo lattice

TL;DR

This study visualizes the emergence of heavy fermionic excitations in a quantum critical Kondo lattice using spectroscopic mapping, revealing their energy-momentum structure, mass enhancement, and critical damping near quantum criticality.

Contribution

It provides direct spectroscopic evidence of heavy quasiparticle formation and their properties in a cerium-based heavy-fermion compound, highlighting quantum entanglement effects.

Findings

Detection of heavy quasiparticles with decreasing temperature

Resolution of their energy-momentum structure through interference patterns

Observation of energy-temperature scaling and critical damping effects

Abstract

In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behaviour observed in actinide- and lanthanide-based compounds. Here we use spectroscopic mapping with the scanning tunnelling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunnelling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system.