We propose a finite-temperature phase diagram for the two-dimensional spin-1/2 J1-J2 XXZ antiferromagnet on a triangular lattice. Our analysis, based on a composite fermion representation, yields several phases. This includes a zero-temperature helical spin liquid with N=6 anisotropic Dirac cones, and with nonzero vector chirality implying a broken Z2 symmetry. It is terminated at T=0 by a continuous quantum phase transition to a 120° ordered state around J2/J1≈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 J2/J1≃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.
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We are indebted to L. Balents, A. Chernyshev, A. Chubukov, O. Starykh, and Mengxing Ye for valuable discussions. A.K. was supported by NSF Grant No. DMR-1608238. T.A.S. acknowledges startup funds from UMass Amherst and thanks the Max Planck Institute for the Physics of Complex Systems for hospitality.
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