Kagome Antiferromagnet: A Chiral Topological Spin Liquid?

TLDR

A recent instability toward a chiral phase in the classical Heisenberg model on the kagome lattice motivates the investigation. The authors propose a specific chiral spin liquid that reconciles established results for both classical and quantum kagome systems. They analyze this proposal using an extended mean‑field Schwinger‑boson framework that incorporates time‑reversal symmetry breaking phases. Quantum fluctuations stabilize a chiral phase robust to second‑ and third‑neighbor perturbations, and for spin‑1/.

Abstract

Inspired by the recent discovery of a new instability towards a chiral phase of the classical Heisenberg model on the kagome lattice, we propose a specific chiral spin liquid that reconciles different, well-established results concerning both the classical and quantum models. This proposal is analyzed in an extended mean-field Schwinger boson framework encompassing time reversal symmetry breaking phases, which allows both a classical and a quantum phase description. At low temperatures, we find that quantum fluctuations favor this chiral phase, which is stable against small perturbations of second- and third-neighbor interactions. For spin-$1/2$, this phase may be, beyond the mean field, a chiral gapped spin liquid. Such a phase is consistent with the density matrix renormalization group results of Yan et al. [Science 332, 1173 (2011)]. Mysterious features of the low-lying excitations of exact diagonalization spectra also find an explanation in this framework. Moreover, thermal fluctuations compete with quantum ones and induce a transition from this flux phase to a planar zero flux phase at a nonzero value of the renormalized temperature ($T/{\mathcal{S}}^{2}$), reconciling these results with those obtained for the classical system.