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

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.

Magnetic Kondo regimes in a frustrated half-filled trimer

“…While in the existing literature the trimer phase diagrams were investigated mainly at vanishing temperature, we show that the T → 0 limit is irrelevant for experiments in certain parameter regimes. Moreover, even though quantum impurity systems often can generally be understood in terms of a few stable T → 0 phases and the QPTs between them [28,31,[81][82][83][84][85][86], a number of cases where continuous crossovers significantly alter the physics are also known [87][88][89][90], especially in the context of the competition between the Kondo effect and the spin polarization caused by the ferromagnetic leads [91][92][93].…”