Orbitally driven spin-singlet dimerization in S=1 La4Ru2O10.
Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation + Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.
Wu
Hua
H
II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
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Burnus
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Denlinger
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Khalifah
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Mandrus
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Jang
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Hsieh
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Tanaka
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Liang
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Allen
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Cava
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Khomskii
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Tjeng
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