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Regular version of the site

Article

Long-range spin correlations in a honeycomb spin model with magnetic field

JETP Letters. 2016. Vol. 103. No. 2. P. 117-121.

We consider the spin-1/2 model on the honeycomb lattice [A. Kitaev, Ann. Phys.321, 2 (2006)] in the presence of a weak magnetic field h≪J. Such a perturbation treated in the lowest nonvanishing order over h leads [K.S. Tikhonov, M.V. Feigel’man, and A.Yu. Kitaev, Phys. Rev. Lett.106, 067203 (2011)] to a power-law decay of irreducible spin correlations 〈〈sz(t,r)sz(0, 0)〉〉∝f(t,r), wheref(t,r)∝[max(t,Jr)]–4. We have studied the effects of the next order of perturbation in h and found an additional term of the order in the correlation function 〈〈sz(t,r)sz(0, 0)〉〉 which scales as cos(γ)/r^3 at Jt≪r, where γ is the polar angle in the 2Dplane. We demonstrate that such a contribution can be understood as a result of a perturbation of the effective Majorana Hamiltonian by the weak imaginary vector potential Ax∝i