Kinetic Ferromagnetism and Topological Magnons of the Hole-Doped Kitaev Spin Liquid

TL;DR

This paper investigates how hole doping affects the Kitaev spin liquid, revealing that even a single hole can induce ferromagnetic order and topological magnons, with implications for real materials.

Contribution

It introduces a combined numerical and theoretical study showing doping-induced ferromagnetism and topological magnons in the Kitaev spin liquid, including a mean-field theory explanation.

Findings

Single hole doping disrupts fractionalization and induces ferromagnetic polarization.

Material-relevant anisotropic exchange drives a reorientation to a topological FM state.

Doping leads to topological magnon excitations with experimental signatures.

Abstract

We study the effect of hole doping on the Kitaev spin liquid (KSL) and find that for ferromagnetic (FM) Kitaev exchange $K$ the system is very susceptible to the formation of a FM spin polarization. Through density matrix renormalization group (DMRG) simulations on finite systems, we uncover that the introduction of a single hole with a hopping strength of just $t\sim{}0.28K$ is enough to disrupt fractionalization and polarize the spins in the [001] direction due to an order-by-disorder mechanism. Taking into account a material relevant FM anisotropic spin exchange $\varGamma$ drives the polarization towards the [111] direction via a reorientation transition into a topological FM state with chiral magnon excitations. We develop a parton mean-field theory incorporating fermionic holons and bosonic spinons/magnons, which accounts for the doping induced FM phases and topological magnon excitations. We discuss experimental signatures and implications for Kitaev candidate materials.