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Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface

Abstract

Many-body interactions in transition-metal oxides give rise to a wide range of functional properties, such as high-temperature superconductivity1, colossal magnetoresistance2 or multiferroicity 3. The seminal recent discovery of a two-dimensional electron gas (2DEG) at the interface of the insulating oxides LaAlO3 and SrTiO3 (ref. 4) represents an important milestone towards exploiting such properties in all-oxide devices5. This conducting interface shows a number of appealing properties, including a high electron mobility4,6, superconductivity7 and large magnetoresistance8, and can be patterned on the few-nanometre length scale. However, the microscopic origin of the interface 2DEG is poorly understood. Here, we show that a similar 2DEG, with an electron density as large as 8×1013 cm−2, can be formed at the bare SrTiO3 surface. Furthermore, we find that the 2DEG density can be controlled through exposure of the surface to intense ultraviolet light. Subsequent angle-resolved photoemission spectroscopy measurements reveal an unusual coexistence of a light quasiparticle mass and signatures of strong many-body interactions.

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Figure 1: Observation of a surface 2DEG on SrTiO3 after exposure of the cleaved (100) surface to synchrotron (ultraviolet) light.
Figure 2: Variation of 2DEG charge density with exposure to different ultraviolet irradiation doses.
Figure 3: Calculations of quantized 2DEG states within a band-bending model20.
Figure 4: Comparison of ARPES data from SrTiO3, InAs and Bi2Sr2CuO6 samples.

References

  1. 1

    Bednorz, J. G. & Muller, K. A. Perovskite-type oxides: The new approach to high-Tc superconductivity. Rev. Mod. Phys. 60, 585–600 (1988).

    CAS  Article  Google Scholar 

  2. 2

    Von Helmolt, R. et al. Giant negative magnetoresistance in perovskitelike La2/3Ba1/3MnOx ferromagnetic films. Phys. Rev. Lett. 71, 2331–2333 (1993).

    CAS  Article  Google Scholar 

  3. 3

    Kimura, T. et al. Magnetic control of ferroelectric polarization. Nature 426, 55–58 (2003).

    CAS  Article  Google Scholar 

  4. 4

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

    CAS  Article  Google Scholar 

  5. 5

    Takagi, H. & Hwang, H. Y. An emergent change of phase for electronics. Science 327, 1601–1602 (2010).

    CAS  Article  Google Scholar 

  6. 6

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

    CAS  Article  Google Scholar 

  7. 7

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

    CAS  Article  Google Scholar 

  8. 8

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

    CAS  Article  Google Scholar 

  9. 9

    Cen, C. et al. Nanoscale control of an interfacial metal–insulator transition at room temperature. Nature Mater. 7, 298–302 (2008).

    CAS  Article  Google Scholar 

  10. 10

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

    CAS  Article  Google Scholar 

  11. 11

    Siemons, W. et al. Origin of charge density at LaAlO3 on SrTiO3 heterointerfaces: Possibility of intrinsic doping. Phys. Rev. Lett. 98, 196802 (2007).

    Article  Google Scholar 

  12. 12

    Kalabukhov, A. et al. Effect of oxygen vacancies in the SrTiO3 substrate on the electrical properties of the LaAlO3/SrTiO3 interface. Phys. Rev. B 75, 121404(R) (2007).

    Article  Google Scholar 

  13. 13

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

    CAS  Article  Google Scholar 

  14. 14

    Meevasana, W. et al. Strong energy–momentum dispersion of phonon-dressed carriers in the lightly doped band insulator SrTiO3 . New. J. Phys. 12, 023004 (2010).

    Article  Google Scholar 

  15. 15

    Kozuka, Y. et al. Optically tuned dimensionality crossover in photocarrier-doped SrTiO3: Onset of weak localization. Phys. Rev. B 76, 085129 (2007).

    Article  Google Scholar 

  16. 16

    Mochizuki, S. et al. Photoluminescence and reversible photo-induced spectral change of SrTiO3 . J. Phys. Condens. Matter 17, 923–948 (2005).

    CAS  Article  Google Scholar 

  17. 17

    Aiura, Y. et al. Photoemission study of the metallic state of lightly electron-doped SrTiO3 . Surf. Sci. 515, 61–74 (2002).

    CAS  Article  Google Scholar 

  18. 18

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

    CAS  Article  Google Scholar 

  19. 19

    Xie, Y. et al. Charge writing at the LaAlO3/SrTiO3 surface. Nano Lett. 10, 2588–2591 (2010).

    CAS  Article  Google Scholar 

  20. 20

    King, P. D. C., Veal, T. D. & McConville, C. F. Non-parabolic coupled Poisson–Schrodinger solutions for quantized electron accumulation layers: Band bending, charge profile, and subbands at InN surfaces. Phys. Rev. B 77, 125305 (2008).

    Article  Google Scholar 

  21. 21

    Copie, O. et al. Towards two-dimensional metallic behavior at LaAlO3/SrTiO3 interfaces. Phys. Rev. Lett. 102, 216804 (2009).

    CAS  Article  Google Scholar 

  22. 22

    Popović, Z. S., Satpathy, S. & Martin, R. M. Origin of the two-dimensional electron gas carrier density at the LaAlO3 or SrTiO3 interface. Phys. Rev. Lett. 101, 256801 (2008).

    Article  Google Scholar 

  23. 23

    King, P. D. C. et al. Surface electron accumulation and the charge neutrality level in In2O3 . Phys. Rev. Lett. 101, 116808 (2008).

    CAS  Article  Google Scholar 

  24. 24

    King, P. D. C. et al. Surface band gap narrowing in quantized electron accumulation layers. Phys. Rev. Lett. 104, 256803 (2010).

    CAS  Article  Google Scholar 

  25. 25

    Meevasana, W. et al. Hierarchy of multiple many-body interaction scales in high-temperature superconductors. Phys. Rev. B 75, 174506 (2007).

    Article  Google Scholar 

  26. 26

    Breitschaft, M. et al. Two-dimensional electron liquid state at LaAlO3–SrTiO3 interfaces. Phys. Rev. B 81, 153414 (2010).

    Article  Google Scholar 

  27. 27

    Li, L. et al. Large capacitance enhancement and negative compressibility of two-dimensional electronic systems at LaAlO3/SrTiO3 interfaces. Preprint at http://arxiv.org/pdf/1006.2847 (2010).

  28. 28

    Colakerol, L. et al. Quantized electron accumulation states in indium nitride studied by angle-resolved photoemission spectroscopy. Phys. Rev. Lett. 97, 237601 (2006).

    Article  Google Scholar 

Download references

Acknowledgements

We would like to thank H. Y. Hwang, H. Takagi, M. R. Beasley, J. L. M. van Mechelen, D. van der Marel, P. Reunchan and S. Limpijumnong for helpful discussions. W.M. would like to thank H. Nakajima and Y. Rattanachai for help with the resistivity measurement. The work at ALS and Stanford Institute for Materials and Energy Sciences is supported by DOE’s Office of Basic Energy Sciences under Contracts No. DE-AC02-76SF00515 and DE-AC03-76SF00098. The work at St. Andrews is supported by the UK-EPSRC (EP/F006640/1) and the ERC (207901). W.M. acknowledges The Thailand Research Fund, Office of the Higher Education Commission and Suranaree University of Technology for financial support.

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ARPES measurements were carried out by W.M., P.D.C.K., R.H.H., F.B. and A.T. W.M. and P.D.C.K. analysed the ARPES data. W.M., P.D.C.K. and F.B. wrote the paper with suggestions and comments by R.H.H., S-K.M. and Z-X.S. Calculations of quantized 2DEG states were done by P.D.C.K. S-K.M. and M.H. maintained the ARPES endstation. Resistivity measurements were carried out by W.M. and P.S. Z-X.S. and F.B. are responsible for project direction, planning and infrastructure.

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Correspondence to Z-X. Shen.

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The authors declare no competing financial interests.

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Meevasana, W., King, P., He, R. et al. Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface. Nature Mater 10, 114–118 (2011). https://doi.org/10.1038/nmat2943

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