Instability of the Fermi-liquid fixed point in an extended Kondo model

TL;DR

This paper investigates an extended SU(N) Kondo model with mixed impurity representations, revealing that the strong coupling fixed point can be unstable, leading to complex screening behaviors relevant for non-Fermi liquid phenomena.

Contribution

It introduces a novel extended Kondo model with combined fermionic and bosonic impurity descriptions, analyzing its fixed point stability and impurity screening mechanisms.

Findings

Strong coupling fixed point can be unstable under certain conditions.

Impurity may attract electrons, causing a double-stage Kondo effect.

Stability region aligns with partial electron repulsion at neighboring sites.

Abstract

We study an extended SU(N) single-impurity Kondo model in which the impurity spin is described by a combination of Abrikosov fermions and Schwinger bosons. Our aim is to describe both the quasiparticle-like excitations and the locally critical modes observed in various physical situations, including non-Fermi liquid (NFL) behavior in heavy fermions in the vicinity of a quantum critical point and anomalous transport properties in quantum wires. In contrast with models with either pure bosonic or pure fermionic impurities, the strong coupling fixed point is unstable against the conduction electron kinetic term under certain conditions. The stability region of the strong coupling fixed point coincides with the region where the partially screened, effective impurity repels the electrons on adjacent sites. In the instability region, the impurity tends to attract $(N-1)$ electrons to the neighboring sites, giving rise to a double-stage Kondo effect with additional screening of the impurity.