Long-range spin correlations in a honeycomb spin model with magnetic field
A. V. Lunkin+*, K. S. Tikhonov+*, M. V. Feigel'man+*
+Landau Institute for Theoretical Physics of the RAS, 119334 Moscow, Russia
*Moscow Institute of Physics and Technology, 141700 Moscow, Russia
We consider spin-1/2 model on the honeycomb lattice
(Ann. Phys. 321, 2 (2006))
in presence of weak magnetic field .
Such a perturbation treated in the lowest nonvanishing order over hα
leads (Phys. Rev. Lett. 106, 067203 (2011))
to a power-law decay of irreducible spin correlations
, where .
In the present Letter we studied the effects of the next order of
in hz and found an additional term of the order hz4 in the correlation
function which scales as
at , where γ is the polar
angle in the 2D plane. We demonstrate that such a contribution can be
as a result of a perturbation of the effective Majorana Hamiltonian by
weak imaginary vector potential .