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Abstract

We propose a finite-temperature phase diagram for the two-dimensional spin-1/2 J(1) - J(2) 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 Z(2) symmetry. It is terminated at T = 0 by a continuous quantum phase transition to a 120 degrees ordered state around J(2)/J(1) approximate to 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) similar or equal to 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.