Competition between Kondo and Kitaev Physics in Kitaev clusters coupled to a fermionic bath

TL;DR

This paper investigates the competition between Kondo screening and Kitaev interactions in quantum impurity clusters coupled to a fermionic bath, revealing complex ground states and fractionalized excitations through Numerical Renormalization Group analysis.

Contribution

It introduces a detailed NRG study of Kitaev clusters coupled to fermionic baths, mapping the complex impurity to an effective two-impurity system and analyzing fractionalization effects.

Findings

Kondo and Kitaev physics compete depending on coupling strengths.

In the Kondo limit, the impurity maps to an effective two-impurity system with Majorana and flux degrees of freedom.

Unscreened flux degrees of freedom persist in tetrahedral clusters despite interactions.

Abstract

Geometrically frustrated quantum impurities coupled to metallic leads have been shown to exhibit rich behavior with a quantum phase transition separating Kondo screened and local moment phases. Frustration in the quantum impurity can alternatively be introduced via Kitaev-couplings between different spins of the impurity cluster. We use the Numerical Renormalization Group (NRG) to study a range of systems where the quantum impurity comprising a Kitaev cluster is coupled to a bath of non-interacting fermions. The models exhibits a competition between Kitaev and Kondo dominated physics depending on whether the Kitaev couplings are greater or less than the Kondo temperature. We characterize the ground state properties of the system and determine the temperature dependence of the crossover scale for the emergence of fractionalized degrees of freedom in the model. We also demonstrate qualitatively as well as quantitatively that in the Kondo limit, the complex impurity can be mapped to an effective two-impurity system, where the emergent spin $1/2$ comprises of both Majorana and flux degrees of freedom. For a tetrahedral-shaped Kitaev cluster, an extra orbital degree of freedom closely related to a flux degree of freedom remains unscreened even in the presence of both Heisenberg and Kondo interactions.