Letter

Coexistence of magnetic order and two-dimensional superconductivity at LaAlO3/SrTiO3 interfaces

Received:
Accepted:
Published online:

Abstract

A two-dimensional electronic system forms at the interface between the band insulators1,2 LaAlO3 and SrTiO3. Samples fabricated until now have been found to be either magnetic or superconducting, depending on growth conditions3,4. Combining high-resolution magnetic torque magnetometry and transport measurements, we report here magnetization measurements providing direct evidence of magnetic ordering of the two-dimensional electron liquid at the interface. The magnetic ordering exists from well below the superconducting transition to up to 200 K, and is characterized by an in-plane magnetic moment. Surprisingly, despite the presence of this magnetic ordering, the interface superconducts below 120 mK. This is unusual because conventional superconductivity rarely exists in magnetically ordered metals5,6. Our results suggest that there is either phase separation or coexistence between magnetic and superconducting states. The coexistence scenario would point to an unconventional superconducting phase as the ground state.

  • Subscribe to Nature Physics for full access:

    $59

    Subscribe

Additional access options:

Already a subscriber?  Log in  now or  Register  for online access.

References

  1. 1.

    & A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature 427, 423–426 (2004).

  2. 2.

    et al. Tunable quasi-two dimensional electron gases in oxide heterostructures. Science 313, 1942–1945 (2006).

  3. 3.

    et al. Superconducting interfaces between insulating oxides. Science 317, 1196–1199 (2007).

  4. 4.

    et al. Magnetic effects at the interface between non-magnetic oxides. Nature Mater. 6, 493–496 (2007).

  5. 5.

    & Superconductivity in a strong spin-exchange field. Phys. Rev. 135, A550–A563 (1964).

  6. 6.

    & Inhomogenous state of superconductors. Sov. Phys. JETP. 20, 762 (1965).

  7. 7.

    et al. Antiferromagnetic ordering of Ru and Gd in superconducting RuSr2GdCu2O8. Phys. Rev. B 61, 14964–14967 (2000).

  8. 8.

    et al. Superconductivity in ferromagnetic RuSr2GdCu2O8. Phys. Rev. Lett. 83, 3713–3716 (1999).

  9. 9.

    et al. Superconductivity at the border of itinerant electron ferromagnetism in UGe2. Nature 406, 587–592 (2000).

  10. 10.

    et al. Anisotropic magnetotransport at the SrTiO3/LaAlO3 interface. Phys. Rev. B 80, 140403(R) (2009).

  11. 11.

    & Antisymmetric magnetoresistance of the SrTiO3/LaAlO3 interface. Phys. Rev. B 80, 180410 (2009).

  12. 12.

    et al. Electronic phase separation at the LaAlO3/SrTiO3 interface. Nature Comm. 2, 188–194 (2011).

  13. 13.

    , & Lattice relaxation in oxide heterostructures: LaAlO3/SrTiO3 superlattices. Phys. Rev. Lett. 97, 056802 (2006).

  14. 14.

    & Charge localization or itineracy at LaAlO3/SrTiO3 interfaces: Hole polarons, oxygen vacancies, and mobile electrons. Phys. Rev. B 74, 035112 (2006).

  15. 15.

    et al. Magnetism of LaAlO3/SrTiO3 superlattices. J. Appl. Phys. 103, 07B508 (2008).

  16. 16.

    & Electronic-structure-induced reconstruction and magnetic ordering at the LaAlO3|SrTiO3 interface. Europhys. Lett. 84, 27001 (2008).

  17. 17.

    & Structural relaxation and metal–insulator transition at the interface between SrTiO3 and LaAlO3. Surf. Sci. 605, 1114–1121 (2011).

  18. 18.

    et al. Structure–property relation of SrTiO3/LaAlO3 interfaces. Adv. Mater. 21, 1665–1677 (2009).

  19. 19.

    et al. Anomalous magneto-transport at the superconducting interface between LaAlO3 and SrTiO3. Physica C 470, 1–2 (2010).

  20. 20.

    et al. Experimental evidence for a transverse magnetization of the Abrikosov lattice in anisotropic superconductors. Phys. Rev. Lett 61, 2805–2808 (1988).

  21. 21.

    et al. A multi-component Fermi surface in the vortex state of an underdoped high Tc superconductor. Nature 454, 200–203 (2008).

  22. 22.

    et al. Low temperature vortex liquid in La2−xSrxCuO4. Nature Phys. 3, 311–314 (2007).

  23. 23.

    The Physical Principles of Magnetism (John Wiley, 1965).

  24. 24.

    , , & Magnetism and superconductivity at LAO/STO-interfaces both generated by the Ti 3d interface electrons? Preprint at .

  25. 25.

    , , & Direct magnetization measurement of the LaAlO3/SrTiO3 heterostructure. Abstract #A34.009 APS March Meeting 2011, American Physical Society, 21–25 March (2011).

  26. 26.

    et al. Coexistence of superconductivity and ferromagnetism in two dimensions. Phys. Rev. Lett. 107, 056802 (2011).

  27. 27.

    et al. Hysteretic magneto-resistance at the LaAlO3–SrTiO3 interface—interplay between superconducting and ferromagnetic properties. Abstract #A34.012 APS March Meeting 2011, American Physical Society, 21–25 March (2011).

  28. 28.

    et al. Direct imaging of the coexistence of ferromagnetism and suprconductivity at the LaAlO3/SrTiO3 interface. Nature Phys. 7 (2011).

Download references

Acknowledgements

The authors acknowledge discussions with D. Grundler, T. Kopp, P. A. Lee and G. A. Sawatzky, and experimental assistance from T. Murphy, J-H. Park and S. Hannahs. This work was supported by the Army Research Office (54173PH), by the Deutsche Forschungsgemeinschaft (TRR 80) and by the EC (OxIDes). L.L. would like to thank the MIT Pappalardo Fellowships in Physics for their support. The high-field experiments were performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement DMR-084173, by the State of Florida and by the DOE.

Author information

Affiliations

  1. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Lu Li
    •  & R. C. Ashoori
  2. Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany

    • C. Richter
  3. Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany

    • J. Mannhart

Authors

  1. Search for Lu Li in:

  2. Search for C. Richter in:

  3. Search for J. Mannhart in:

  4. Search for R. C. Ashoori in:

Contributions

The studies were designed, planned and analysed by all authors, who also wrote the manuscript. C.R. grew the samples; L.L. carried out the torque and resistivity measurements and the data analysis.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to R. C. Ashoori.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information