Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering

TL;DR

This study uses resonant inelastic x-ray scattering to observe how localized electronic states in a Kondo system hybridize with conduction electrons, revealing momentum-dependent features that deepen understanding of correlated metal behaviors.

Contribution

It provides direct experimental evidence of high-energy state hybridization in a Kondo lattice, highlighting the role of spin-orbit excited states in correlated electron phenomena.

Findings

Spin-orbit excited states show momentum dependence at low temperature

Localized degrees of freedom hybridize with metallic states

Results inform microscopic models of correlated materials

Abstract

Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd$_3$ to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature - the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.