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Orbitally driven spin-singlet dimerization in $S$=1 La$_{4}$Ru$_{2}$O$_{10}$

Hua Wu·Z. Hu·T. Burnus·J. D. Denlinger·P. G. Khalifah·D. Mandrus·L. -Y. Jang·H. H. Hsieh·A. Tanaka·K. S. Liang·J. W. Allen·R. J. Cava·D. I. Khomskii·L. H. Tjeng
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Abstract

Using x-ray absorption spectroscopy at the Ru-$L_{2,3}$ edge we reveal that the Ru$^{4+}$ 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 (LSDA+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 La$_{4}$Ru$_{2}$O$_{10}$ appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi 2-dimensional $S$=1 system.

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Hua Wu, Z. Hu, T. Burnus, J. D. Denlinger, P. G. Khalifah, D. Mandrus, L. -Y. Jang, H. H. Hsieh, A. Tanaka, K. S. Liang, J. W. Allen, R. J. Cava, D. I. Khomskii, L. H. Tjeng. 2006-06-20. Orbitally driven spin-singlet dimerization in $S$=1 La$_{4}$Ru$_{2}$O$_{10}$. https://doi.org/10.1103/physrevlett.96.256402

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