Nonlocal Kondo effect and two-fluid picture revealed in an exactly solvable model

TL;DR

This paper presents an exactly solvable model revealing how nonlocal Kondo interactions lead to a continuous Fermi surface evolution and two-fluid behavior, offering microscopic insights into heavy fermion phenomena.

Contribution

The authors introduce a novel exactly solvable Kondo-Heisenberg model with momentum-space spins, elucidating the microscopic origin of two-fluid behavior and Fermi surface evolution in heavy fermion systems.

Findings

Continuous Fermi surface evolution with Kondo interaction

Observation of two-fluid behavior similar to experiments

Violation of traditional Luttinger's theorem with a generalized version

Abstract

Understanding the nature of local-itinerant transition of strongly correlated electrons is one of the central problems in condensed matter physics. Heavy fermion systems describe the f-electron delocalization through Kondo interactions with conduction electrons. Tremendous efforts have been devoted to the so-called Kondo-destruction scenario, which predicts a dramatic local-to-itinerant quantum phase transition of f-electrons at zero temperature. On the other hand, two-fluid behaviors have been observed in many materials, suggesting coexistence of local and itinerant f-electrons over a broad temperature range but lacking a microscopic theoretical description. To elucidate this fundamental issue, here we propose an exactly solvable Kondo-Heisenberg model in which the spins are defined in the momentum space and the k-space Kondo interaction corresponds to a highly nonlocal spin scattering in the coordinate space. Its solution reveals a continuous evolution of the Fermi surfaces with Kondo interaction and two-fluid behaviors similar to those observed in real materials. The electron density violates the usual Luttinger's theorem, but follows a generalized one allowing for partially enlarged Fermi surfaces due to partial Kondo screening in the momentum space. Our results highlight the consequence of nonlocal Kondo interaction relevant for strong quantum fluctuation regions, and provide important insight into the microscopic description of two-fluid phenomenology in heavy fermion systems.