Critical hybridization for the Kondo resonance in gapless systems

TL;DR

This paper investigates the Kondo resonance in gapless systems with a single impurity Anderson model, revealing how strong correlations induce a Kondo-like peak below the Fermi level, with findings supported by renormalization group comparisons.

Contribution

It introduces an analysis of the Kondo resonance in gapless systems using the equation of motion approach, highlighting the conditions for a sharp impurity spectral peak and comparing with renormalization group results.

Findings

Strong electron-electron correlations induce a sharp Kondo-like peak.

The peak appears below the Fermi level in systems with depleted density of states.

Results are consistent with renormalization group approaches.

Abstract

We study the Kondo resonance in a spin-1/2 single impurity Anderson model with a gapless conduction band using the equation of motion approach in order to obtain the impurity spectral function. We study two different scenarios for gapless systems: a purely power-law energy dependence of the density of states or a constant density of states with a gapless behavior near the Fermi level. We demonstrate that strong electron-electron correlations lead to a sharp peak in the impurity spectral function in the case of a large exchange coupling ($J>J_{c}$) or equivalently, a strong hybridization ($V>V_{c}$). This Kondo-like peak emerges much below the Fermi level in the case of a strongly depleted density of states. These results are compared with the ones from renormalization group approaches.