Instabilities of the Fractionalized Dirac Semimetal in the Kitaev-Kondo Model

TL;DR

This paper investigates the stability of a fractionalized Dirac semimetal in a honeycomb Kondo lattice model, revealing instabilities towards antiferromagnetic order and disfavoring superconductivity through RG analysis.

Contribution

It introduces a perturbative RG analysis of a Kitaev-Kondo model showing how fractionalization leads to specific electronic instabilities.

Findings

Electrons decouple from Majorana fermions at criticality.

All three electron interactions become positive under RG.

The fractionalized Fermi liquid is unstable to antiferromagnetic order.

Abstract

We study a honeycomb Kondo lattice model in which Dirac conduction electrons are coupled to a spin-1/2 Kitaev quantum spin liquid. For weak Kondo coupling, the spins fractionalize into Majorana fermions comprising a gapless Dirac mode and three gapped visons. In second order perturbation theory, the Kondo coupling gives rise to local Hubbard repulsions and spin-spin interactions between conduction electrons, as well as a vertex coupling electrons to gapless Majorana fermions. We analyze the resulting low-energy field theory using a perturbative renormalization group (RG) scheme, accounting for additional density-density interactions generated under RG. At criticality, electrons decouple from Majorana fermions but all three electron interactions acquire positive values. An analysis of susceptibility exponents reveals that the fractionalized Fermi liquid becomes unstable towards antiferromagnetic order and that superconductivity is disfavored.