Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Spin–orbital separation in the quasi-one-dimensional Mott insulator Sr2CuO3

This article has been updated


When viewed as an elementary particle, the electron has spin and charge. When binding to the atomic nucleus, it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies. Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers: spin, charge and orbital1. The hallmark of one-dimensional physics is a breaking up of the elementary electron into its separate degrees of freedom2. The separation of the electron into independent quasi-particles that carry either spin (spinons) or charge (holons) was first observed fifteen years ago3. Here we report observation of the separation of the orbital degree of freedom (orbiton) using resonant inelastic X-ray scattering on the one-dimensional Mott insulator Sr2CuO3. We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum, of about 0.2 electronvolts, over nearly one Brillouin zone.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Spin–orbital separation process in an antiferromagnetic spin chain, emerging after exciting an orbital.
Figure 2: Energy dependence of elementary excitations in Sr 2 CuO 3 observed with RIXS at the copper L 3 -edge resonance.
Figure 3: Dispersion of magnetic excitations: experimental data and simulation.
Figure 4: Dispersion of orbital excitations: comparison between experiment and ab initio calculations.

Change history

  • 02 May 2011

    An axis label was replaced on Fig. 4c.


  1. 1

    Kugel’, K. I. & Khomskii, D. I. The Jahn-Teller effect and magnetism: transition metal compounds. Sov. Phys. Usp. 25, 231–256 (1982)

    Article  ADS  Google Scholar 

  2. 2

    Giamarchi, T. Quantum Physics in One Dimension (Clarendon Press, 2004)

    MATH  Google Scholar 

  3. 3

    Kim, C. et al. Observation of spin-charge separation in one-dimensional SrCuO2 . Phys. Rev. Lett. 77, 4054–4057 (1996)

    CAS  Article  ADS  Google Scholar 

  4. 4

    Fujisawa, H. et al. Angle-resolved photoemission study of Sr2CuO3 . Phys. Rev. B 59, 7358–7361 (1999)

    CAS  Article  ADS  Google Scholar 

  5. 5

    Kim, B. J. et al. Distinct spinon and holon dispersions in photoemission spectral functions from one-dimensional SrCuO2 . Nature Phys. 2, 397–401 (2006)

    CAS  Article  ADS  Google Scholar 

  6. 6

    Anderson, P. W. The resonating valence bond state in La2CuO4 and superconductivity. Science 235, 1196–1198 (1987)

    CAS  Article  ADS  Google Scholar 

  7. 7

    Senthil, T. & Fisher, M. P. A. Fractionalization in the cuprates: detecting the topological order. Phys. Rev. Lett. 86, 292–295 (2001)

    CAS  Article  ADS  Google Scholar 

  8. 8

    Wohlfeld, K., Daghofer, M., Nishimoto, S., Khaliullin, G. & van den Brink, J. Intrinsic coupling of orbital excitations to spin fluctuations in Mott insulators. Phys. Rev. Lett. 107, 147201 (2011)

    Article  ADS  Google Scholar 

  9. 9

    Ament, L., van Veenendaal, M., Devereaux, T., Hill, J. P. & van den Brink, J. Resonant inelastic X-ray scattering studies of elementary excitations. Rev. Mod. Phys. 83, 705–767 (2011)

    CAS  Article  ADS  Google Scholar 

  10. 10

    Moretti Sala, M. et al. Energy and symmetry of dd excitations in undoped layered cuprates measured by Cu L3 resonant inelastic x-ray scattering. N. J. Phys. 13, 043026 (2011)

    Article  Google Scholar 

  11. 11

    Ament, L. J. P., Ghiringhelli, G., Moretti Sala, M. & Braicovich, L. &. van den Brink, J. Theoretical demonstration of how the dispersion of magnetic excitations in cuprate compounds can be determined using resonant inelastic x-ray scattering. Phys. Rev. Lett. 103, 117003 (2009)

    Article  ADS  Google Scholar 

  12. 12

    Luo, J., Trammell, G. T. & Hannon, J. P. Scattering operator for elastic and inelastic resonant x-ray scattering. Phys. Rev. Lett. 71, 287–290 (1993)

    CAS  Article  ADS  Google Scholar 

  13. 13

    Haverkort, M. W. Theory of resonant inelastic X-ray scattering by collective magnetic excitations. Phys. Rev. Lett. 105, 167404 (2010)

    CAS  Article  ADS  Google Scholar 

  14. 14

    Schlappa, J. et al. Collective magnetic excitations in the spin ladder Sr14Cu24O41 Measured using high-resolution resonant inelastic X-Ray scattering. Phys. Rev. Lett. 103, 047401 (2009)

    CAS  Article  ADS  Google Scholar 

  15. 15

    Braicovich, L. et al. Magnetic excitations and phase separation in the underdoped La2-xSrxCuO4 superconductor measured by resonant inelastic X-ray scattering. Phys. Rev. Lett. 104, 077002 (2010)

    CAS  Article  ADS  Google Scholar 

  16. 16

    Le Tacon, M. et al. Intense paramagnon excitations in a large family of high-temperature superconductors. Nature Phys. 7, 725–730 (2011)

    CAS  Article  ADS  Google Scholar 

  17. 17

    Strocov, V. N. et al. High-resolution soft X-ray beamline ADRESS at the Swiss Light Source for resonant inelastic X-ray scattering and angle-resolved photoelectron spectroscopies. J. Synchrotron Radiat. 17, 631–643 (2010)

    CAS  Article  Google Scholar 

  18. 18

    Ghiringhelli, G. et al. SAXES, a high resolution spectrometer for resonant x-ray emission in the 400–1600 eV energy range. Rev. Sci. Instrum. 77, 113108 (2006)

    Article  ADS  Google Scholar 

  19. 19

    Hozoi, L., Siurakshina, L., Fulde, P. & van den Brink, J. Ab initio determination of Cu 3d orbital energies in layered copper oxides. Sci. Rep. 1, 1–4 (2011)

    Article  Google Scholar 

  20. 20

    Walters, A. C. et al. Effect of covalent bonding on magnetism and the missing neutron intensity in copper oxide compounds. Nature Phys. 5, 867–872 (2009)

    CAS  Article  ADS  Google Scholar 

  21. 21

    Glawion, S. et al. Two-spinon and orbital excitations of the spin-Peierls system TiOCl. Phys. Rev. Lett. 107, 107402 (2011)

    CAS  Article  ADS  Google Scholar 

  22. 22

    Caux, J.-S. & Hagemans, R. The four-spinon dynamical structure factor of the Heisenberg chain. J. Stat. Mech. 2006, P12013 (2006)

    Article  Google Scholar 

  23. 23

    Oleś, A. M., Khaliullin, G., Horsch, P. & Feiner, L. F. Fingerprints of spin-orbital physics in cubic Mott insulators: magnetic exchange interactions and optical spectral weights. Phys. Rev. B 72, 214431 (2005)

    Article  ADS  Google Scholar 

  24. 24

    Neudert, R. et al. Four-band extended Hubbard Hamiltonian for the one-dimensional cuprate Sr2CuO3: distribution of oxygen holes and its relation to strong intersite Coulomb interaction. Phys. Rev. B 62, 10752–10765 (2000)

    CAS  Article  ADS  Google Scholar 

  25. 25

    Brunner, M. Assaad, F. F. & Muramatsu, A. Single hole dynamics in the one dimensional t-J model. Eur. Phys. J. B 16, 209–212 (2000)

    CAS  Article  ADS  Google Scholar 

  26. 26

    Suzuura, H. & Nagaosa, N. Spin-charge separation in angle-resolved photoemission spectra. Phys. Rev. B 56, 3548–3551 (1997)

    CAS  Article  ADS  Google Scholar 

  27. 27

    Macfarlane, R. M. & Allen, J. W. Exciton bands in antiferromagnetic Cr2O3 . Phys. Rev. B 4, 3054–3067 (1971)

    Article  ADS  Google Scholar 

  28. 28

    Grüninger, M. et al. Experimental quest for orbital waves. Nature 418, 39–40 (2002)

    Article  ADS  Google Scholar 

  29. 29

    Ulrich, C. et al. Momentum dependence of orbital excitations in Mott-insulating titanates. Phys. Rev. Lett. 103, 107205 (2009)

    CAS  Article  ADS  Google Scholar 

  30. 30

    van Veenendaal, M. Polarization dependence of L- and M-edge resonant inelastic X-ray scattering in transition-metal compound. Phys. Rev. Lett. 96, 117404 (2006)

    Article  ADS  Google Scholar 

Download references


This work was performed at the ADRESS beamline of the Swiss Light Source using the SAXES instrument jointly built by the Paul Scherrer Institut, Switzerland, and Politecnico di Milano, Italy. We acknowledge support from the Swiss National Science Foundation and its NCCR MaNEP. K.W. acknowledges support from the Alexander von Humboldt foundation and discussions with M. Daghofer and S.-L. Drechsler. J.-S.C. acknowledges support from the Foundation for Fundamental Research on Matter and from the Netherlands Organisation for Scientific Research. S.S. and A.R. acknowledge the support of the European contract NOVMAG. This research benefited from the RIXS collaboration supported by the Computational Materials Science Network programme of the Division of Materials Science and Engineering, US Department of Energy, grant no. DE-SC0007091.

Author information




J.S., T.S. and H.M.R. planned the experiment. S.S. and A.R. fabricated the samples. J.S., K.J.Z., V.N.S. and T.S. carried out the experiment. J.S. and M.M. carried out the data analysis. C.M. helped with the data analysis. K.W. and J.v.d.B. developed the theory for the spin–orbital separation with assistance from M.W.H., L.H. and S.N. J.-S.C. provided the theory for the spin excitations. J.S., K.W., K.J.Z., H.M.R., J.v.d.B. and T.S. wrote the paper with contributions from all co-authors. L.P., H.M.R., J.v.d.B. and T.S. supervised the project.

Corresponding authors

Correspondence to J. Schlappa or T. Schmitt.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data, Supplementary Table 1, Supplementary Figures 1-4 and additional references. (PDF 4088 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Schlappa, J., Wohlfeld, K., Zhou, K. et al. Spin–orbital separation in the quasi-one-dimensional Mott insulator Sr2CuO3. Nature 485, 82–85 (2012).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links