1202.1610 (Yue Yu et al.)

Symmetric spin-orbtial-Hubbard model on honeycomb lattice: An origin of
Kitaev model and beyond    [PDF]

Yue Yu, Shaojing Qin

We present a single band Hubbard model on honeycomb lattice with
link-symmetric spin-orbital interaction. In the large $U$ limit, this model is
mapped to a conventional antiferromangentic (AFM) Heisenberg model combining
with a 'zig-zag' AFM Heisenberg one. The latter AFM order was favored by recent
experiments for A$_2$IrO$_3$ (A=Na, Li) [4-6]. Competition between two
different AFM orders leads to a spin liquid phase characterized by Kitaev model
that happens if the spin-orbital coupling has the same strength as the hopping
amplitude. This deepens our understanding of the origin of the Kitaev coupling:
It comes from the balance between the hopping and spin-orbital couplings but to
get rid of the hopping. In a moderate $U$, this model has a charge-spin gapped
phase with two different spinon excitations. In a weak interaction, the
original gapless Dirac fermion is gapped by the spin-orbital coupling while a
new gapless Dirac fermion appears at the same Dirac points.

View original: http://arxiv.org/abs/1202.1610