Numerical evidence for a chiral spin liquid in the XXZ antiferromagnetic Heisenberg model on the kagome lattice at $m=\frac{2}{3}$ magnetization

Abstract

We perform an exact diagonalization study of the spin-$1/2$ XXZ Heisenberg antiferromagnet on the kagome lattice at finite magnetization $m = \frac{2}{3}$ with an emphasis on the XY point ($J_z = 0$), and in the presence of a small chiral term. Recent analytic work by Kumar, Sun and Fradkin [Phys. Rev. B 90, 174409 (2014)] on the same model, using a newly developed flux attachment transformation, predicts a plateau at this value of the magnetization described by a chiral spin liquid (CSL) with a spin Hall conductance of $\sigma_{xy} = \frac{1}{2}$. Such a state is topological in nature, has a ground state degeneracy and exhibits fractional excitations. We analyze the degeneracy structure in the low energy manifold, identify the candidate topological states and use them to compute the modular matrices and Chern numbers all of which strongly agree with expected theoretical behavior for the $\sigma_{xy} = \frac{1}{2}$ CSL. We argue that the evidence suggests the CSL is robust even in the limit of zero external chirality.