The honeycomb iridates A2IrO3 (A=Na, Li) constitute promising candidate
materials to realize the Heisenberg-Kitaev model (HKM) in nature, hosting
unconventional magnetic as well as spin liquid phases. Recent experiments
suggest, however, that Li2IrO3 exhibits a magnetically ordered state of
incommensurate spiral type which has not been identified in the HKM. We show
that these findings can be understood in the context of an extended
Heisenberg-Kitaev scenario satisfying all tentative experimental evidence: (i)
the maximum of the magnetic susceptibility is located inside the first
Brillouin zone, (ii) the Curie-Weiss temperature is negative relating to
dominant antiferromagnetic fluctuations, and (iii) significant second-neighbor
spin-exchange is involved.Comment: 5 pages, 5 figures, selected as an Editors' suggestio
