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


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.


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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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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).

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