S. A. Kulagin, N. Prokof'ev, O. A. Starykh, B. Svistunov, C. N. Varney
We demonstrate, by considering the triangular lattice spin-1/2 Heisenberg model, that Monte Carlo sampling of skeleton Feynman diagrams within the fermionization framework offers a universal first-principles tool for strongly correlated lattice quantum systems. We observe the fermionic sign blessing---cancellation of higher order diagrams leading to a finite convergence radius of the series. We calculate magnetic susceptibility of the triangular-lattice quantum antiferromagnet in the correlated paramagnet regime and reveal surprising---numerically exact---microscopic correspondence with its classical counterpart at all accessible temperatures. Extrapolation of the observed relation to zero temperature suggests the absence of the magnetic order in the ground state. We critically examine implications of this unusual scenario.
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http://arxiv.org/abs/1212.0055
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