Spin gap and string order parameter in the ferromagnetic Spiral Staircase Heisenberg Ladder: a quantum Monte Carlo study
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 (\theta) deformation of the ladder and interpolates between the isotropic ladder (\theta=0) and the SU(2) ferromagnetic Kondo necklace model (\theta=\pi). We show that the ground state in the (\theta,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 \Delta/J_\| \propto J_\perp/J_\| for \theta < \theta_c \simeq 8\pi/9 to \Delta/J_\| \propto (J_\perp/J_\|)^2 for \theta > \theta_c. Those results are obtained on the basis of large scale Quantum Monte Carlo calculations.
Keywords
Cite
@article{arxiv.0706.2769,
title = {Spin gap and string order parameter in the ferromagnetic Spiral Staircase Heisenberg Ladder: a quantum Monte Carlo study},
author = {C. Brünger and F. F. Assaad and S. Capponi and F. Alet and D. N. Aristov and M. N. Kiselev},
journal= {arXiv preprint arXiv:0706.2769},
year = {2008}
}
Comments
4 pages