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 α ≪ J. Such a perturbation treated in the lowest nonvanishing order over h α leads [K.S. Tikhonov, M.V. Feigel'man, and A.Yu. Kitaev, Phys. Rev. Lett. 106, 067203 (2011)] to a powerlaw decay of irreducible spin correlations 《 s z ( t, r) s z (0, 0)》 ∝ h z 2 f( t, r), where f( t, r) ∝ [max( t, Jr)]-4. We have studied the effects of the next order of perturbation in h z and found an additional term of the order h z 4 in the correlation function 《 s z ( t, r) s z (0, 0)》 which scales as h z 4 cosγ/ r 3 at Jt≪ r, where γ is the polar angle in the 2D plane. 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 A x ∝ i h z 2.
Soviet Journal of Experimental and Theoretical Physics Letters
- Pub Date:
- January 2016
- Condensed Matter - Strongly Correlated Electrons
- 8 pages, 2 figures. Extended and corrected version of the paper published in JETP Lett. v.103, p.117 (2016)