%0 Journal Article
%T Unified theory of spiral magnetism in the harmonic-honeycomb iridates ¦Á, ¦Â, ¦Ã Li2IrO3
%A Itamar Kimchi
%A Radu Coldea
%A Ashvin Vishwanath
%J Physics
%D 2014
%I arXiv
%R 10.1103/PhysRevB.91.245134
%X A family of insulating iridates with chemical formula Li$_2$IrO$_3$ has recently been discovered, featuring three distinct crystal structures $\alpha,\beta,\gamma$ (honeycomb, hyperhoneycomb, stripyhoneycomb). Measurements on the three-dimensional polytypes, $\beta$- and $\gamma$-Li$_2$IrO$_3$, found that they magnetically order into remarkably similar spiral phases, exhibiting a non-coplanar counter-rotating spiral magnetic order with equivalent q=0.57 wavevectors. We examine magnetic Hamiltonians for this family and show that the same triplet of nearest-neighbor Kitaev-Heisenberg-Ising (KJI) interactions reproduces this spiral order on both $\beta,\gamma$-Li$_2$IrO$_3$ structures. We analyze the origin of this phenomenon by studying the model on a 1D zigzag chain, a structural unit common to the three polytypes. The zigzag-chain solution transparently shows how the Kitaev interaction stabilizes the counter-rotating spiral, which is shown to persist on restoring the inter-chain coupling. Our minimal model makes a concrete prediction for the magnetic order in $\alpha$-Li$_2$IrO$_3$.
%U http://arxiv.org/abs/1408.3640v3