Fractionalized Superconductivity Mediated by Majorana Fermions in the Kitaev-Kondo Lattice

TL;DR

This paper introduces a model where superconductivity arises from a fractionalized non-Fermi liquid state in a Kitaev--Kondo lattice, showing coexistence of conventional pairing with a spin-liquid background and topological order.

Contribution

It demonstrates the existence of a fractionalized superconducting phase in the Kitaev--Kondo lattice, characterized by unconventional pairing and topological order, using perturbation theory and functional renormalization group.

Findings

Fractionalized superconducting phase exists at weak Kondo coupling.

Cooper pairing coexists with a spin-liquid background and topological order.

Pairing symmetry depends on the sign of the Kitaev coupling, being either chiral d-wave or p-wave.

Abstract

Superconductivity usually emerges from a metallic normal state which follows the Fermi-liquid paradigm. If, in contrast, the normal state is a fractionalized non-Fermi liquid, then pairing may either eliminate fractionalization via a Higgs-type mechanism leading to a conventional superconducting state, or pairing can occur in the presence of fractionalization. Here we discuss a simple model for the latter case: Using a combination of perturbation theory and functional renormalization group, we show that the Kitaev--Kondo lattice model displays a fractionalized superconducting phase at weak Kondo coupling. This phase is characterized by Cooper pairing of conventional electronic quasiparticles, coexisting with a spin-liquid background and topological order. Depending on the sign of the Kitaev coupling, we find the pairing to be either of chiral $d$-wave or $p$-wave type for extended doping regions around the van-Hove filling. We discuss applications and extensions.