Letter | Published:

Direct observation of a two-dimensional hole gas at oxide interfaces

Nature Materialsvolume 17pages231236 (2018) | Download Citation

Abstract

The discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface1 has resulted in the observation of many properties2,3,4,5 not present in conventional semiconductor heterostructures, and so become a focal point for device applications6,7,8. Its counterpart, the two-dimensional hole gas (2DHG), is expected to complement the 2DEG. However, although the 2DEG has been widely observed9, the 2DHG has proved elusive. Herein we demonstrate a highly mobile 2DHG in epitaxially grown SrTiO3/LaAlO3/SrTiO3 heterostructures. Using electrical transport measurements and in-line electron holography, we provide direct evidence of a 2DHG that coexists with a 2DEG at complementary heterointerfaces in the same structure. First-principles calculations, coherent Bragg rod analysis and depth-resolved cathodoluminescence spectroscopy consistently support our finding that to eliminate ionic point defects is key to realizing a 2DHG. The coexistence of a 2DEG and a 2DHG in a single oxide heterostructure provides a platform for the exciting physics of confined electron–hole systems and for developing applications.

  • Subscribe to Nature Materials for full access:

    $59

    Subscribe

Additional access options:

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

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  1. 1.

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

  2. 2.

    Thiel, S., Hammerl, G., Schmehl, A., Schneider, C. W. & Mannhart, J. Tunable quasi-two-dimensional electron gases in oxide heterostructures. Science 313, 1942–1945 (2006).

  3. 3.

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

  4. 4.

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

  5. 5.

    Caviglia, A. D. et al. Electric field control of the LaAlO3/SrTiO3 interface ground state. Nature 456, 624–627 (2008).

  6. 6.

    Mannhart, J. & Schlom, D. G. Oxide interfaces—an opportunity for electronics. Science 327, 1607–1611 (2010).

  7. 7.

    Cheng, G. L. et al. Sketched oxide single-electron transistor. Nat. Nanotech. 6, 343–347 (2011).

  8. 8.

    Lesne, E. et al. Highly efficient and tunable spin-to-charge conversion through Rashba coupling at oxide interfaces. Nat. Mater. 15, 1261–1266 (2016).

  9. 9.

    Mannhart, J., Blank, D. H. A., Hwang, H. Y., Millis, A. J. & Triscone, J. M. Two-dimensional electron gases at oxide interfaces. MRS Bull. 33, 1027–1034 (2008).

  10. 10.

    Nakagawa, N., Hwang, H. Y. & Muller, D. A. Why some interfaces cannot be sharp. Nat. Mater. 5, 204–209 (2006).

  11. 11.

    Huijben, M. et al. Electronically coupled complementary interfaces between perovskite band insulators. Nat. Mater. 5, 556–560 (2006).

  12. 12.

    Herranz, G. et al. High mobility in LaAlO3/SrTiO3 heterostructures: origin, dimensionality, and perspectives. Phys. Rev. Lett. 98, 216803 (2007).

  13. 13.

    Hwang, H. Y. et al. Emergent phenomena at oxide interfaces. Nat. Mater. 11, 103–113 (2012).

  14. 14.

    Chen, Y. Z. et al. Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces by charge-transfer-induced modulation doping. Nat. Mater. 14, 801–806 (2015).

  15. 15.

    Pentcheva, R. & Pickett, W. E. Charge localization or itineracy at LaAlO3/SrTiO3 interfaces: hole polarons, oxygen vacancies, and mobile electrons. Phys. Rev. B 74, 035112 (2006).

  16. 16.

    Park, M. S., Rhim, S. H. & Freeman, A. J. Charge compensation and mixed valency in LaAlO3/SrTiO3 heterointerfaces studied by the FLAPW method. Phys. Rev. B 74, 205416 (2006).

  17. 17.

    Pentcheva, R. et al. Parallel electron–hole bilayer conductivity from electronic interface reconstruction. Phys. Rev. Lett. 104, 166804 (2010).

  18. 18.

    Huijben, M. et al. Local probing of coupled interfaces between two-dimensional electron and hole gases in oxide heterostructures by variable-temperature scanning tunneling spectroscopy. Phys. Rev. B 86, 035140 (2012).

  19. 19.

    Zhong, Z. C., Xu, P. X. & Kelly, P. J. Polarity-induced oxygen vacancies at LaAlO3/SrTiO3 interfaces. Phys. Rev. B 82, 165127 (2010).

  20. 20.

    Rubano, A. et al. Influence of atomic termination on the LaAlO3/SrTiO3 interfacial polar rearrangement. Phys. Rev. B 88, 035405 (2013).

  21. 21.

    Cancellieri, C. et al. Polaronic metal state at the LaAlO3/SrTiO3 interface. Nat. Commun. 7, 10386 (2016).

  22. 22.

    Luo, W. D., Duan, W. H., Louie, S. G. & Cohen, M. L. Structural and electronic properties of n-doped and p-doped SrTiO3. Phys. Rev. B 70, 214109 (2004).

  23. 23.

    Himmetoglu, B., Janotti, A., Peelaers, H., Alkauskas, A. & Van de Walle, C. G. First-principles study of the mobility of SrTiO3. Phys. Rev. B 90, 241204 (2014).

  24. 24.

    Koch, C. T. A flux-preserving non-linear inline holography reconstruction algorithm for partially coherent electrons. Ultramicroscopy 108, 141–150 (2008).

  25. 25.

    Muller, D. A., Nakagawa, N., Ohtomo, A., Grazul, J. L. & Hwang, H. Y. Atomic-scale imaging of nanoengineered oxygen vacancy profiles in SrTiO3. Nature 430, 657–661 (2004).

  26. 26.

    Caviglia, A. D. et al. Tunable Rashba spin–orbit interaction at oxide interfaces. Phys. Rev. Lett. 104, 126803 (2010).

  27. 27.

    Millis, A. J. & Schlom, D. G. Electron–hole liquids in transition-metal oxide heterostructures. Phys. Rev. B 82, 073101 (2010).

  28. 28.

    Szymanska, M. H. & Littlewood, P. B. Excitonic binding in coupled quantum wells. Phys. Rev. B 67, 193305 (2003).

  29. 29.

    Tse, W. K. & Das Sarma, S. Coulomb drag and spin drag in the presence of spin–orbit coupling. Phys. Rev. B 75, 045333 (2007).

  30. 30.

    Eisenstein, J. P. & MacDonald, A. H. Bose–Einstein condensation of excitons in bilayer electron systems. Nature 432, 691–694 (2004).

  31. 31.

    Bark, C. W. et al. Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain. Proc. Natl Acad. Sci. USA 108, 4720–4724 (2011).

  32. 32.

    Bi, F. et al. Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface. Nat. Commun. 5, 5019 (2014).

  33. 33.

    Blochl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

  34. 34.

    Kresse, G. & Furthmuller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).

  35. 35.

    Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).

  36. 36.

    Zhou, H. et al. Anomalous expansion of the copper–apical-oxygen distance in superconducting cuprate bilayers. Proc. Natl Acad. Sci. USA 107, 8103–8107 (2010).

  37. 37.

    Zhou, H., Pindak, R., Clarke, R., Steinberg, D. M. & Yacoby, Y. The limits of ultrahigh-resolution X-ray mapping: estimating uncertainties in thin-film and interface structures determined by phase retrieval methods. J. Phys. D. 45, 195302 (2012).

  38. 38.

    Koch, C. T. Towards full-resolution inline electron holography. Micron 63, 69–75 (2014).

  39. 39.

    Janolin, P. E. Strain on ferroelectric thin films. J. Mater. Sci. 44, 5025–5048 (2009).

  40. 40.

    Zhang, J. et al. Depth-resolved subsurface defects in chemically etched SrTiO3. Appl. Phys. Lett. 94, 092904 (2009).

  41. 41.

    Brillson, L. J. Applications of depth-resolved cathodoluminescence spectroscopy. J. Phys. D. 45, 183001 (2012).

  42. 42.

    Asel, T. J. et al. Near-nanoscale-resolved energy band structure of LaNiO3/La2/3Sr1/3MnO3/SrTiO3 heterostructures and their interfaces. J. Vac. Sci. Technol. B 33, 04E103 (2015).

  43. 43.

    Rutkowski, M. M., McNicholas, K., Zeng, Z. Q., Tuomisto, F. & Brillson, L. J. Optical identification of oxygen vacancy formation at SrTiO3–(Ba,Sr)TiO3 heterostructures. J. Phys. D. 47, 255303 (2014).

Download references

Acknowledgements

This work was supported by the National Science Foundation (NSF) under DMREF Grant number DMR-1629270, AFOSR under award number FA9550-15-1-0334 and AOARD under award number FA2386-15-1-4046. Transport measurement at the University of Wisconsin-Madison was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under award number DE-FG02-06ER46327. Research at the University of Nebraska-Lincoln was supported by the NSF MRSEC (Grant no. DMR-1420645). T.J.A. and L.J.B. acknowledge support from NSF grant DMR 1305193. Use of the Advanced Photon Source was supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under Contract no. DE-AC02-06CH11357. STEM and in-line electron holography works by S.H.O. were supported by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2015M3D1A1070672) and NRF grant funded by the Korea government (NRF-2015R1A2A2A01007904).

Author information

Affiliations

  1. Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA

    • H. Lee
    • , J. W. Lee
    •  & C. B. Eom
  2. Department of Physics, University of Wisconsin-Madison, Madison, WI, USA

    • N. Campbell
    •  & M. S. Rzchowski
  3. Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Korea

    • J. Lee
    • , J. Seo
    • , B. Park
    •  & S. H. Oh
  4. Department of Physics, The Ohio State University, Columbus, OH, USA

    • T. J. Asel
    • , B. Noesges
    •  & L. J. Brillson
  5. Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA

    • T. R. Paudel
    •  & E. Y. Tsymbal
  6. X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA

    • H. Zhou
  7. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Korea

    • B. Park
  8. Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH, USA

    • L. J. Brillson

Authors

  1. Search for H. Lee in:

  2. Search for N. Campbell in:

  3. Search for J. Lee in:

  4. Search for T. J. Asel in:

  5. Search for T. R. Paudel in:

  6. Search for H. Zhou in:

  7. Search for J. W. Lee in:

  8. Search for B. Noesges in:

  9. Search for J. Seo in:

  10. Search for B. Park in:

  11. Search for L. J. Brillson in:

  12. Search for S. H. Oh in:

  13. Search for E. Y. Tsymbal in:

  14. Search for M. S. Rzchowski in:

  15. Search for C. B. Eom in:

Contributions

H.L. and C.B.E. conceived the project. C.B.E., M.S.R., E.Y.T., S.H.O. and L.J.B. supervised the experiments. H.L., J.W.L. and C.B.E. fabricated and characterized the thin-film samples. N.C. and M.S.R. carried out the electrical transport measurements. J.L., B.P., J.S. and S.H.O. carried out the STEM and in-line holography measurements. T.J.A. and B.N. performed the DR-CLS measurements. T.R.P. and E.Y.T. performed the theoretical calculations. H.Z. performed the synchrotron diffraction measurements. H.L., N.C., J.L., T.A., T.R.P., H.Z. and C.B.E. prepared the manuscript. C.B.E. directed the overall research.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to C. B. Eom.

Supplementary information

  1. Supplementary Information

    Supplementary Information.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/s41563-017-0002-4

Rights and permissions

To obtain permission to re-use content from this article visit RightsLink.