A Kagome Map of Spin Liquids: from XXZ to Dzyaloshinskii-Moriya Ferromagnet

TL;DR

This paper introduces an exact three-fold mapping on the kagome lattice that unifies various magnetic models, revealing extensive classical degeneracy and a network of quantum spin liquids, with implications for materials like Herbertsmithite.

Contribution

It presents a novel exact mapping transforming Heisenberg and XXZ models on kagome into time-reversal invariant Hamiltonians, unifying classical and quantum spin liquid behaviors.

Findings

Classical ground states exhibit extensive degeneracy.

Quantum XXZ model maps to a network of spin liquids.

Overlap with phase diagram of Herbertsmithite ZnCu3(OH)6Cl2.

Abstract

The kagome lattice sits at the crossroad of present research efforts in quantum spin liquids, chiral phases, emergent skyrmion excitations and anomalous Hall effects to name but a few. In light of this diversity, our goal in this paper is to build a unifying picture of the underlying magnetic degrees-of-freedom on kagome. Motivated by a growing mosaic of materials, we especially consider a broad range of nearest-neighbour interactions consisting of Dzyaloshinskii-Moriya as well as anisotropic ferro$-$ and antiferromagnetic coupling. We present a three-fold mapping on the kagome lattice which transforms the celebrated Heisenberg antiferromagnet and XXZ model onto two lines of time-reversal invariant Hamiltonians. The mapping is exact for classical and quantum spins alike, i.e. it preserves the energy spectrum of the original Heisenberg and XXZ models. As a consequence, at the classical level, all phases have an extensive ground-state degeneracy. These ground states support a variety of phenomena such as ferromagnetically induced pinch points in the structure factor and the possibility for spontaneous scalar chirality. For quantum spin$-1/2$, the XXZ model has been recently shown to be a quantum spin liquid. Applying our three-fold mapping to the XXZ model gives rise to a connected network of quantum spin liquids, centered around a paragon of quantum disorder, namely the Ising antiferromagnet. We show that this quantum disorder spreads over an extended region of the phase diagram at linear order in spin wave theory, which overlaps with the parameter region of Herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$. We conclude this work by discussing the connection of our results to the chiral spin liquids found on kagome with further nearest-neighbour interactions, and to the recently synthesized ternary intermetallic materials.