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arXiv · 0706.2769

Spin gap and string order parameter in the ferromagnetic Spiral Staircase Heisenberg Ladder: a quantum Monte Carlo study

C. Brünger·F. F. Assaad·S. Capponi·F. Alet·D. N. Aristov·M. N. Kiselev
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Abstract

We consider a spin-1/2 ladder with a ferromagnetic rung coupling J_\perp and inequivalent chains. This model is obtained by a twist (θ) deformation of the ladder and interpolates between the isotropic ladder (θ=0) and the SU(2) ferromagnetic Kondo necklace model (θ=π). We show that the ground state in the (θ,J_\perp) plane has a finite string order parameter characterising the Haldane phase. Twisting the chain introduces a new energy scale, which we interpret in terms of a Suhl-Nakamura interaction. As a consequence we observe a crossover in the scaling of the spin gap at weak coupling from Δ/J_\| \propto J_\perp/J_\| for θ< θ_c \simeq 8π/9 to Δ/J_\| \propto (J_\perp/J_\|)^2 for θ> θ_c. Those results are obtained on the basis of large scale Quantum Monte Carlo calculations.

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C. Brünger, F. F. Assaad, S. Capponi, F. Alet, D. N. Aristov, M. N. Kiselev. 2007-06-25. Spin gap and string order parameter in the ferromagnetic Spiral Staircase Heisenberg Ladder: a quantum Monte Carlo study. https://doi.org/10.1103/physrevlett.100.017202

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