Chiral spin liquid on kagome antiferromagnet induced by Dzyaloshinskii-Moriya interaction

TL;DR

This paper predicts a new chiral Z2 spin liquid phase in kagome antiferromagnets with Dzyaloshinskii-Moriya interaction, explaining experimental neutron scattering data and revealing a stable, small-gap quantum spin liquid at low DMI.

Contribution

It introduces a novel chiral Z2 spin liquid phase at small DMI using Schwinger-boson mean-field theory, clarifying the nature of the small-DMI regime in kagome antiferromagnets.

Findings

Identifies a stable chiral Z2 spin liquid with a small, constant spin gap.

Provides a phase diagram as a function of DMI and spin size.

Matches neutron scattering spectra with the proposed phase.

Abstract

The quantum spin liquid material herbertsmithite is described by an antiferromagnetic Heisenberg model on the kagome lattice with non-negligible Dzyaloshinskii-Moriya interaction~(DMI). A well established phase transition to the $\mathbf q=0$ long-range order occurs in this model when the DMI strength increases, but the precise nature of a small-DMI phase remains controversial. Here, we describe a new phase obtained from Schwinger-boson mean-field theory that is stable at small DMI, and which can explain the dispersionless spectrum seen in inelastic neutron scattering experiment by Han et al (Nature (London) 492, 406 (2012)}). It is a time-reversal symmetry breaking $\mathbb Z_2$ spin liquid, with the unique property of a small and constant spin gap in an extended region of the Brillouin zone. The phase diagram as a function of DMI and spin size is given, and dynamical spin structure factors are presented.