Magnetic impurities in the honeycomb Kitaev model

TL;DR

This paper investigates how magnetic impurities interact with the honeycomb Kitaev spin liquid, revealing an unconventional Kondo effect and a unique long-range impurity interaction mediated by spinons, dependent on impurity spin size and coupling.

Contribution

It introduces a novel analysis of magnetic impurity effects in the Kitaev model, highlighting an unusual Kondo fixed point and a distinctive long-range interaction mediated by spinons.

Findings

Unusual Kondo effect with an intermediate fixed point at coupling K_c J/S.

Long-range impurity interactions mediated by massless spinons, differing from RKKY.

Impurity interactions depend on impurity coupling to multiple spins and impurity spin size.

Abstract

We study the effect of coupling magnetic impurities to the honeycomb lattice spin-1/2 Kitaev model in its spin liquid phase. We show that a spin-S impurity coupled to the Kitaev model is associated with an unusual Kondo effect with an intermediate coupling unstable fixed point K_c J/S separating topologically distinct sectors of the Kitaev model. We also show that the massless spinons in the spin liquid mediate an interaction of the form S_{i\alpha}^{2}S_{j\beta}^{2}/R_{ij}^{3} between distant impurities unlike the usual dipolar RKKY interaction S_{i\alpha}S_{j\alpha}/R_{ij}^{3} noted in various 2D impurity problems with a pseudogapped density of states of the spin bath. Furthermore, this long-range interaction is possible only if the impurities (a) couple to more than one neighboring spin on the host lattice and (b) the impurity spin is not a spin-1/2.$