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

TL;DR

This paper presents a finite-temperature phase diagram for a 2D triangular lattice spin-1/2 XXZ antiferromagnet, revealing a helical spin liquid with anisotropic Dirac cones and broken symmetry, and analyzing phase transitions and experimental implications.

Contribution

It introduces a novel helical spin liquid phase with anisotropic Dirac cones in the triangular XXZ model using Chern-Simons theory, and details the phase transitions and symmetry properties.

Findings

Identification of a helical spin liquid with 6 anisotropic Dirac cones

Continuous quantum phase transition at J2/J1≈0.089

First-order transition into stripe phase at J2/J1≈0.116

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 $J_2/J_1\approx0.089$ 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.