Fractionalized Fermi liquids and exotic superconductivity in the Kitaev-Kondo lattice

TL;DR

This paper explores a Kondo lattice model on a honeycomb lattice that hosts fractionalized Fermi liquid phases and uncovers novel triplet superconducting phases driven by Majorana fermions, revealing complex phase transitions.

Contribution

It introduces a concrete model with FL* phases based on Kitaev's spin liquid and maps out a phase diagram including exotic superconductivity driven by Majorana fermions.

Findings

Identification of FL* phases in the Kitaev-Kondo lattice model

Discovery of triplet superconducting phases masked by quantum phase transitions

Superconductivity driven by Majorana fermion pairing structure

Abstract

Fractionalized Fermi liquids (FL$^\ast$) have been introduced as non-Fermi-liquid metallic phases, characterized by coexisting electron-like charge carriers and local moments which itself form a fractionalized spin liquid. Here we investigate a Kondo lattice model on the honeycomb lattice with compass interactions among the local moments, a concrete model hosting FL$^\ast$ phases based on Kitaev's $\mathbb{Z}_2$ spin liquid. We characterize the FL$^\ast$ phases via perturbation theory, and we employ a Majorana-fermion mean-field theory to map out the full phase diagram. Most remarkably we find triplet superconducting phases which mask the quantum phase transition between fractionalized and conventional Fermi liquid phases. Their pairing structure is inherited from the Kitaev spin liquid, i.e., superconductivity is driven by Majorana glue.