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arXiv · 1408.3640

Unified theory of spiral magnetism in the harmonic-honeycomb iridates α, β, γ Li2IrO3

Itamar Kimchi·Radu Coldea·Ashvin Vishwanath
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Abstract

A family of insulating iridates with chemical formula Li$_2$IrO$_3$ has recently been discovered, featuring three distinct crystal structures $α,β,γ$ (honeycomb, hyperhoneycomb, stripyhoneycomb). Measurements on the three-dimensional polytypes, $β$- and $γ$-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 $β,γ$-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 $α$-Li$_2$IrO$_3$.

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Itamar Kimchi, Radu Coldea, Ashvin Vishwanath. 2015-06-15. Unified theory of spiral magnetism in the harmonic-honeycomb iridates α, β, γ Li2IrO3. https://doi.org/10.1103/physrevb.91.245134

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