Classical dimers in orbitaly degenrate Honeycomb AFM

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Classical Dimers in Orbitally Degenerate Honeycomb
Antiferromagnet
George Jackeli
Max-Planck Institute for Solid State Research,
Stuttgart
In collaboration with Daniel Khomskii Univ.
of Cologne
Phys. Rev. Lett. 08
Krakow, 18-22 June 2008
GNSF 06-81-4-100 KITP PHY05-51164
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Miura et. al., JPSJ07
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Miura et. al., JPSJ07
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Ru4 (d4), S1 3-fold orbital
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Coupled spin-orbital model
Orbital degrees are static Potts-like!
Exchange couplings
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The ground state manifold
Ground state manifold is spanned by hard-core
dimer coverings
Extensive orientational degeneracy infinitely
many ways of covering
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Lifting the orientational degeneracy of dimers
Possible Mechanisms
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Order-out-of-disorder by triplet fluctuations
Fluctuations disfavor hexagonal loops, but do not
fully lift the degeneracy
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Degeneracy breaking by magnetoelastic coupling
Elastic energy
Magnetoelastic coupling
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Dimer Jahn-Teller mechanism
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Dimerized pattern and orbital order
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Summary
Orbital induced dimensionality reduction
Spin gap formation and spontaneous dimerization
in Dgt1
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Summary
t2g -systems with dimer ground states
(Theory)