Orbitally driven spin-singlet dimerization in S = 1 La4Ru2O10

Hua Wu,1 Zhiwei Hu,1 Tobias Burnus,1 Jonathan D. Denlinger,2 Peter G. Khalifah,3,4 David G. Mandrus,4 Ling-Yun Jang,5 Hui Huang Hsieh,6 Arata Tanaka,7 Keng S. Liang,5 Jim W. Allen,8 Robert J. Cava,9 Daniel I. Khomskii1 and L. Hao Tjeng1

1 II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
3 Department of Chemistry, University of Massachusetts, Amherst, MA 01003, USA
4 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
5 National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30077, Taiwan
6 Chung Cheng Institute of Technology, National Defense University, Taoyuan 335, Taiwan
7 Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
8 Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109, USA
9 Department of Chemistry, Princeton University, Princeton, NJ 08540, USA

[Abstract][References]

Abstract

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 (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 La4Ru2O10 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.

References

  1. M. Imada, A. Fujimori, and Y. Tokura, Rev. Mod. Phys. 70, 1039 (1998).
  2. Y. Tokura and N. Nagaosa, Science 288, 462 (2000).
  3. A. P. Ramirez, J. Phys.: Conden. Matter 9, 8171 (1997).
  4. D. I. Khomskii and G. A. Sawatzky, Solid State Commun. 102, 87 (1997).
  5. T. Mizokawa and A. Fujimori, Phys. Rev. B 51, 12880 (1995); ibid. 54, 5368 (1996); ibid. 56, R493 (1997).
  6. Y. Ren et al., Nature 396, 441 (1998).
  7. G. R. Blake et al., Phys. Rev. Lett. 87, 245501 (2001).
  8. C. Ulrich et al., Phys. Rev. Lett. 91, 257202 (2003).
  9. J.-H. Park et al., Phys. Rev. B 61, 11506 (2000).
  10. M. W. Haverkort et al., Phys. Rev. Lett. 95, 196404 (2005).
  11. M. Isobe et al., J. Phys. Soc. Jpn. 71, 1423 (2002).
  12. P. G. Radaelli et al., Nature 416, 155 (2002).
  13. M. Schmidt et al., Phys. Rev. Lett. 92, 056402 (2004).
  14. D. I. Khomskii and T. Mizokawa, Phys. Rev. Lett. 94, 156402 (2005).
  15. P. Khalifah et al., Science 297, 2237 (2002).
  16. J. D. Denlinger et al., (unpublished).
  17. F. M. F. de Groot, J. Electron Spectrosc. Relat. Phenom. 67, 529 (1994).
  18. see the Theo Thole Memorial Issue, J. Electron Spectrosc. Relat. Phenom. 86, 1 (1997).
  19. Z. Hu et al., Phys. Rev. B 61, 5262 (2000).
  20. Z. Hu et al., Phys. Rev. Lett. 92, 207402 (2004).
  21. A. Tanaka and T. Jo, J. Phys. Soc. Jpn. 63, 2788 (1994).
  22. T. Mizokawa et al., Phys. Rev. Lett. 87, 077202 (2001); Phys. Rev. B 69, 132410 (2004).
  23. Both La4Ru2O10 and Ca2RuO4 are 2-dimensional and have almost the same octahedral <Ru4+–O> bond lengths and similar t2g bandwidths of about 1.5 eV.
  24. W. A. Harrison, Electronic Structure and the Properties of Solids (Dover, New York, 1989). ISBN 0-486-66021-4
  25. Parameters for RuO6 cluster [eV]: Udd = 3.0, Ucd = 2.0, Δ = 2.0, pdσ = –2.1 for 2.01Å, 10Dq = 1.9, Dt = 0.04, Du = 0.04, Dv = 0.00, ζ = 60% of Hartree-Fock value; Ds = –0.03 (S = 1, HT), –0.06 (S = 1, LT), +0.90 (S = 0, LT).
  26. V. I. Anisimov et al., Phys. Rev. B 48, 16929 (1993).
  27. P. Blaha et al., http://www.wien2k.at.
  28. Z. Fang, N. Nagaosa, and K. Terakura, Phys. Rev. B 69, 045116 (2004).
  29. Using a larger Hubbard U = 5 eV does not change the spin-singlet dimer picture at all, but gives a too large band gap of 1.1 eV.
  30. V. Eyert, S. G. Ebbinghaus, and T. Kopp, Phys. Rev. Lett. 96, 256401 (2006).
  31. Inclusion of the spin-orbit coupling does not affect our conclusions: the xz orbital in the LT phase being lower than the yz and xy by the CFS of &appox;300 meV together with the band formation make the weaker spin-orbit coupling of &appox;150 meV to be less operative. The exchange constants change by less than 5 meV and the orbital moment is small, not more than about 0.2 μB.
  32. R. Osborn, private communication.

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  5. Xianfeng Hao, Yuanhui Xu, Zhijian Wu, Defeng Zhou, Xiaojuan Liu, and Jian Meng, Orbital ordering in Cs2AgF4 from first principles, Phys. Rev. B 76, 054426 (2007).
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  9. Dan Wu, P G Khalifah D G Mandrus and N L Wang, Optical study of the orbital ordered state in La4Ru2O10, J. Phys.: Condens. Matter 20 325204 (2008).