Helical spin liquid in a triangular XXZ magnet from Chern-Simons theory

Abstract

We propose a finite-temperature phase diagram for the 2D spin-$1/2$ $J_1-J_2$ $XXZ$ antiferromagnet on the triangular lattice. Our analysis, based on a composite fermion representation, yields several phases. This includes a zero-temperature helical spin liquid with $N=6$ {\it anisotropic} Dirac cones, and with nonzero vector chirality implying a broken ${\mathbb{Z}}_2$ symmetry. It is terminated at $T=0$ by a continuous quantum phase transition to $120^{\circ }$ ordered state around $J_2/J_1\approx 0.089$ in the XX limit; these phases share a double degeneracy, which persists to finite $T$ above the helical spin liquid. By contrast, at $J_2/J_1\simeq 0.116$, the transition into a stripe phase appears as first order. We further discuss experimental and numerical consequences of the helical order and the anisotropic nature of the Dirac dispersion.

9 pages, 6 figures, Revtex