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Emergent phenomena at oxide interfaces

From magnetism, ferroelectricity and superconductivity to electrical and thermal properties, oxides show a broad range of phenomena of fundamental as well as practical relevance. Reviewed here are the emergent phenomena arising at the interface between oxide materials, which have attracted considerable interest based on advances in thin-film deposition techniques.

Abstract

Recent technical advances in the atomic-scale synthesis of oxide heterostructures have provided a fertile new ground for creating novel states at their interfaces. Different symmetry constraints can be used to design structures exhibiting phenomena not found in the bulk constituents. A characteristic feature is the reconstruction of the charge, spin and orbital states at interfaces on the nanometre scale. Examples such as interface superconductivity, magneto-electric coupling, and the quantum Hall effect in oxide heterostructures are representative of the scientific and technological opportunities in this rapidly emerging field.

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Figure 1
Figure 2: Orbital and spin configurations at interfaces.
Figure 3: Atomic and charge structure of pervoskite heterointerfaces.
Figure 4: Modulation doping of holes using polar surfaces.
Figure 5: Heterostructure of metallic LaNiO3 with partially occupied Ni eg orbitals (LNO, blue) and insulating LaAlO3 (LAO, white)46.
Figure 6: Magnetization induced second-harmonic generation (MSHG) for a tricolour superlattice composed of LaMnO3 (LMO), SrMnO3 (SMO), and LaAlO3 (LAO).
Figure 7: Various device structures used to produce 2D or interface superconductivity.
Figure 8: Fractional quantum Hall effect in ZnO.

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References

  1. Imada, M., Fujimori, A. & Tokura, Y. Metal–insulator transitions. Rev. Mod. Phys. 70, 1039–1262 (1998).

    CAS  Google Scholar 

  2. Heber, J. Enter the oxides. Nature 459, 28–30 (2009).

    CAS  Google Scholar 

  3. Anderson, P. W. More is different. Science 177, 393–396 (1972).

    CAS  Google Scholar 

  4. Bychkov, Y. A. & Rashba, E. I. Properties of a 2D electron gas with lifted spectral degeneracy. J. Exp. Theor. Phys. Lett. 39, 78–81 (1984).

    Google Scholar 

  5. Oka, T. & Nagaosa, N. Interfaces of correlated electron systems: proposed mechanism for colossal electroresistance. Phys. Rev. Lett. 95, 266403 (2005).

    Google Scholar 

  6. Takahashi, K. S., Kawasaki, M. & Tokura, Y. Interface ferromagnetism in oxide superlattices of CaMnO3/CaRuO3 . Appl. Phys. Lett. 79, 1324–1326 (2001).

    CAS  Google Scholar 

  7. Goodenough, J. B. Theory of the role of covalence in the perovskite-type manganites [La, M(II)]MnO3 . Phys. Rev. 100, 564–573 (1955).

    CAS  Google Scholar 

  8. Goodenough, J. B. An interpretation of the magnetic properties of the perovskite-type mixed crystals La1- xSrxCoO3-λ . J. Phys. Chem. Solids 6, 287–297 (1958).

    CAS  Google Scholar 

  9. Kanamori, J. Superexchange interaction and symmetry properties of electron orbitals. J. Phys. Chem. Solids 10, 87–98 (1959).

    CAS  Google Scholar 

  10. Ohtomo, A., Muller, D. A., Grazul, J. L. & Hwang, H. Y. Artificial charge-modulation in atomic-scale perovskite titanate superlattices. Nature 419, 378–380 (2002).

    CAS  Google Scholar 

  11. Tokura, Y. et al. Filling dependence of electronic properties on the verge of metal–Mott-insulator transitions in Sr1- xLaxTiO3 . Phys. Rev. Lett. 72, 2126–2129 (1993).

    Google Scholar 

  12. Salvador, P. A., Haghiri-Gosnet, A-M., Mercey, B., Hervieu, M. & Raveau, B. Growth and magnetoresistive properties of (LaMnO3)m(SrMnO3)n superlattices. Appl. Phys. Lett. 75, 2638–2640 (1999).

    CAS  Google Scholar 

  13. Yamada, H., Kawasaki, M., Lottermoser, T., Arima, T. & Tokura, Y. LaMnO3/SrMnO3 interfaces with coupled charge-spin-orbital modulation. Appl. Phys. Lett. 80, 52506 (2006).

    Google Scholar 

  14. Bhattacharya, A. et al. The metal–insulator transition and its relation to magnetic structure in (LaMnO3)2 n/(SrMnO3)n superlattices. Phys. Rev. Lett. 100, 257203 (2008).

    CAS  Google Scholar 

  15. Gozar, A. et al. High-temperature interface superconductivity between metallic and insulating copper oxides. Nature 455, 782–785 (2008).

    Article  CAS  Google Scholar 

  16. Yuli, O. et al. Enhancement of the superconducting transition temperature of La2- xSrxCuO4 bilayers: role of pairing and phase stiffness. Phys. Rev. Lett. 101, 057005 (2008).

    Google Scholar 

  17. Berg, E., Orgad, D. & Kivelson S. A. Route to high-temperature superconductivity in composite systems. Phys. Rev. B 78, 094509 (2008).

    Google Scholar 

  18. Okamoto, S. & Maier, T. A. Enhanced superconductivity in superlattices of high-TC cuprates. Phys. Rev. Lett. 101, 156401 (2008).

    Google Scholar 

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

    CAS  Google Scholar 

  20. Baraff, G. A., Appelbaum, J. A. & Hamann, D. R. Self-consistent calculation of the electronic structure at an abrupt GaAs-Ge interface. Phys. Rev. Lett. 38, 237–240 (1977).

    CAS  Google Scholar 

  21. Harrison, W. A., Kraut, E. A., Waldrop, J. R. & Grant, R. W. Polar heterojunction interfaces. Phys. Rev. B 18, 4402–4410 (1978).

    CAS  Google Scholar 

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

    CAS  Google Scholar 

  23. Hesper, R., Tjeng, L. H., Heeres, A. & Sawatzky, G. A. Photoemission evidence of electronic stabilization of polar surfaces in K3C60 . Phys. Rev. B 62, 16046–16055 (2000).

    CAS  Google Scholar 

  24. Stengel, M. & Vanderbilt, D. Berry-phase theory of polar discontinuities at oxide-oxide interfaces. Phys. Rev. B 80, 241103(R) (2009).

    Google Scholar 

  25. 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).

    Google Scholar 

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

    Google Scholar 

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

    CAS  Google Scholar 

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

    CAS  Google Scholar 

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

    CAS  Google Scholar 

  30. Xie, Y. W., Bell, C., Yajima, T., Hikita, Y. & Hwang, H. Y. Charge writing at the LaAlO3/SrTiO3 surface. Nano Lett. 10, 2588–2591 (2010).

    CAS  Google Scholar 

  31. Hotta, Y., Susaki, T. & Hwang, H. Y. Polar discontinuity doping of the LaVO3/SrTiO3 interface. Phys. Rev. Lett. 99, 236805 (2007).

    CAS  Google Scholar 

  32. Higuchi, T., Hotta, Y., Susaki, T., Fujimori, A. & Hwang, H. Y. Modulation doping of a Mott quantum well by a proximate polar discontinuity. Phys. Rev. B 79, 075415 (2009).

    Google Scholar 

  33. Lanier, C. H. et al. Surface reconstruction with a fractional hole: (√5×√5)R26.6° LaAlO3 (001). Phys. Rev. Lett. 98, 086102 (2007).

    CAS  Google Scholar 

  34. Takizawa, M. et al. Spectroscopic evidence for competing reconstructions in polar multilayers LaAlO3/LaVO3/LaAlO3 . Phys. Rev. Lett. 102, 236401 (2009).

    CAS  Google Scholar 

  35. Freeland, J. W. et al. Charge transport and magnetization profile at the interface between the correlated metal CaRuO3 and the antiferromagnetic insulator CaMnO3 . Phys. Rev. B 81, 094414 (2010).

    Google Scholar 

  36. Pauli, S. A. et al. Evolution of the interfacial structure of LaAlO3 on SrTiO3 . Phys. Rev. Lett. 106, 036101 (2011).

    CAS  Google Scholar 

  37. Salluzzo, M. et al. Orbital reconstruction and the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 102, 166804 (2009).

    CAS  Google Scholar 

  38. Pinta, C. et al. Suppression of spin-state transition in epitaxially strained LaCoO3 . Phys. Rev. B 78, 174402 (2008).

    Google Scholar 

  39. Aruta, C. et al. Orbital occupation, atomic moments, and magnetic ordering at interfaces of manganite thin films. Phys. Rev. B 80, 014431 (2009).

    Google Scholar 

  40. Okamoto, S. & Millis, A. J. Electronic reconstruction at an interface between a Mott insulator and a band insulator. Nature 428, 630–633 (2004).

    CAS  Google Scholar 

  41. Pentcheva, R. & Pickett, W. E. Correlation-driven charge order at the interface between a Mott and a band insulator. Phys. Rev. Lett. 99, 016802 (2007).

    Google Scholar 

  42. Chaloupka, J. & Khaliullin, G. Orbital order and possible superconductivity in LaNiO3/LaMO3 superlattices. Phys. Rev. Lett. 100, 016404 (2008).

    Google Scholar 

  43. Hansmann, P. et al. Turning a nickelate Fermi surface into a cuprate-like one through heterostructuring. Phys. Rev. Lett. 103, 016401 (2009).

    CAS  Google Scholar 

  44. Han, M. J., Marianetti, C. A. & Millis, A. J. Chemical control of orbital polarization in artificially structured transition-metal oxides: La2NiXO6 (X = B, Al, Ga, In) from first principles. Phys. Rev. B 82, 134408 (2010).

    Google Scholar 

  45. Seo, S. S. A. et al. Two-dimensional confinement of 3d1 electrons in LaTiO3-LaAlO3 multilayers. Phys. Rev. Lett. 104, 036401 (2010).

    CAS  Google Scholar 

  46. Benckiser, E. et al. Orbital reflectometry of oxide heterostructures. Nature Mater. 10, 189–193 (2011).

    CAS  Google Scholar 

  47. Chakhalian, J. et al. Magnetism at the interface between ferromagnetic and superconducting oxides. Nature Phys. 2, 244–248 (2006).

    CAS  Google Scholar 

  48. Chakhalian, J. et al. Orbital reconstruction and covalent bonding at an oxide interface. Science 318, 1114–1117 (2007).

    CAS  Google Scholar 

  49. Yu, P. et al. Interface ferromagnetism and orbital reconstruction in BiFeO3-La0.7Ca0.3MnO3 heterostructures. Phys. Rev. Lett. 105, 027201 (2010).

    CAS  Google Scholar 

  50. Jackeli, G. & Khaliullin, G. Spin, charge, and orbital order at the interface between correlated oxides. Phys. Rev. Lett. 101, 216804 (2008).

    CAS  Google Scholar 

  51. Sai, N., Meyer, B. & Vanderbilt, D. Compositional inversion symmetry breaking in ferroelectric perovskites. Phys. Rev. Lett. 84, 5636–5639 (2000).

    CAS  Google Scholar 

  52. Warusawithana, M. P., Colla, E. V., Eckstein, J. N. & Weissman M. B. Artificial dielectric superlattices with broken inversion symmetry. Phys. Rev. Lett. 90, 036802 (2003).

    Google Scholar 

  53. Lee, H. N., Christen, H. M., Chisholm, M. F., Rouleau, C. M. & Lowndes, D. H. Strong polarization enhancement in asymmetric three-component ferroelectric superlattices. Nature 433, 395–399 (2005).

    CAS  Google Scholar 

  54. Yamada, H., Kawasaki, M., Ogawa, Y. & Tokura, Y. Perovskite oxide tricolor superlattices with artificially broken inversion symmetry by interface effects. Appl. Phys. Lett. 81, 4793–4795 (2002).

    CAS  Google Scholar 

  55. Ogawa, Y. et al. Nonlinear magneto-optical Kerr rotation of an oxide superlattice with artificially broken symmetry. Phys. Rev. Lett. 90, 217403 (2003).

    CAS  Google Scholar 

  56. Kida, N. et al. Optical magnetoelectric effect of patterned oxide superlattices with ferromagnetic interfaces. Phys. Rev. Lett. 99, 197404 (2007).

    CAS  Google Scholar 

  57. Yamada, H. et al. Engineered interface of magnetic oxides. Science 305, 646–648 (2004).

    CAS  Google Scholar 

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

    CAS  Google Scholar 

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

    CAS  Google Scholar 

  60. Bell, C. et al. Dominant mobility modulation by the electric field effect at the LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 103, 226802 (2009).

    CAS  Google Scholar 

  61. Schooley, J. F. et al. Dependence of the superconducting transition temperature on carrier concentration in semiconducting SrTiO3 . Phys. Rev. Lett. 14, 305–307 (1965).

    CAS  Google Scholar 

  62. Ahn, C. H., Triscone, J-M. & Mannhart, J. Electric field effect in correlated oxide systems. Nature 424, 1015–1018 (2003).

    CAS  Google Scholar 

  63. Ueno, K. et al. Electric-field-induced superconductivity in an insulator. Nature Mater. 7, 855–858 (2008).

    CAS  Google Scholar 

  64. Shimotani, H. et al. Insulator-to-metal transition in ZnO by electric double layer gating. Appl. Phys. Lett. 91, 082106 (2007).

    Google Scholar 

  65. Yuan, H. T. et al. High-density carrier accumulation in ZnO field-effect transistors gated by electric double layers of ionic liquids. Adv. Funct. Mater. 19, 1046–1053 (2009).

    CAS  Google Scholar 

  66. Ye, J. T. et al. Gate-induced interface superconductivity on an atomically flat film. Nature Mater. 9, 125–128 (2010).

    CAS  Google Scholar 

  67. Bollinger, A. T. et al. Superconductor–insulator transition in La2−xSrxCuO4 at the pair quantum resistance. Nature 472, 458–460 (2011).

    CAS  Google Scholar 

  68. Kozuka, Y. et al. Enhancing the electron mobility via delta-doping in SrTiO3 . Appl. Phys. Lett. 97, 222115 (2010).

    Google Scholar 

  69. Jalan, B., Stemmer, S., Mack, S. & Allen, S. J. Two-dimensional electron gas in δ-doped SrTiO3 . Phys. Rev. B 82, 081103 (2010).

    Google Scholar 

  70. Kozuka, Y. et al. Two-dimensional normal-state quantum oscillations in a superconducting heterostructure. Nature 462, 487–490 (2009).

    CAS  Google Scholar 

  71. Kim, M. et al. Fermi surface and superconductivity in low-density high-mobility δ-doped SrTiO3 . Phys. Rev. Lett. 107, 106801 (2011).

    CAS  Google Scholar 

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

    CAS  Google Scholar 

  73. Shalom, M. B. et al. Tuning spin-orbit coupling and superconductivity at the SrTiO3/LaAlO3 interface: a magnetotransport study. Phys. Rev. Lett. 104, 126802 (2010).

    Google Scholar 

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

    CAS  Google Scholar 

  75. Li, L., Richter, C., Mannhart, J. & Ashoori, R. C. Coexistence of magnetic order and two-dimensional superconductivity at LaAlO3/SrTiO3 interfaces. Nature Phys. 7, 762–766 (2011).

    CAS  Google Scholar 

  76. Bert, J. A. et al. Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface. Nature Phys. 7, 767–771 (2011).

    CAS  Google Scholar 

  77. Michaeli, K., Potter, A. C. & Lee, P. A. Superconductivity and ferromagnetism in oxide interface structures: possibility of finite momentum pairing. Preprint at http://arXiv.org/abs/1107.4352 (2011).

  78. Stormer, H. L. Nobel Lecture: the fractional quantum Hall effect. Rev. Mod. Phys. 71, 875–889 (1999).

    CAS  Google Scholar 

  79. Tokura, Y. & Hwang, H. Y. Complex oxides on fire. Nature Mater. 7, 694–695 (2008).

    CAS  Google Scholar 

  80. Tsukazaki, A. et al. Quantum Hall effect in polar oxide heterostructures. Science 315, 1388–1391 (2007).

    CAS  Google Scholar 

  81. Tsukazaki, A. et al. Observation of the fractional quantum Hall effect in an oxide. Nature Mater. 9, 889–893 (2010).

    CAS  Google Scholar 

  82. Schlom, D. G. & Pfeiffer L. N. Upward mobility rocks! Nature Mater. 9, 881–883 (2010).

    CAS  Google Scholar 

  83. Kozuka, Y. et al. Insulating phase of a two-dimensional electron gas in MgxZn1- xO/ZnO heterostructures below ν = 1/3. Phys. Rev. B 84, 033304 (2011).

    Google Scholar 

  84. Tanatar, B. & Ceperley, D. Ground state of the two-dimensional electron gas. Phys. Rev. B 39, 5005–5016 (1989).

    CAS  Google Scholar 

  85. Tsukazaki, A. et al. Spin susceptibility and effective mass of two-dimensional electrons in MgxZn1- x/ZnO heterostructures. Phys. Rev. B 78, 233308 (2008).

    Google Scholar 

  86. De Poortere, E. P., Tutuc, E., Papadakis, S. J. & Shayegan, M. Resistance spikes at transitions between quantum Hall ferromagnets. Science 290, 1546–1549 (2000).

    CAS  Google Scholar 

  87. Kroemer, H. Quasi-electric fields and band offsets: teaching electrons new tricks. Nobel Lecture, 8 December 2000; http://go.nature.com/5SFA6C

  88. Waser, R. & Aono, M. Nanoionics-based resistive switching memories. Nature Mater. 6, 833–840 (2007).

    CAS  Google Scholar 

  89. Sawa, A. Resistive switching in transition metal oxides. Mater. Today 11, 28–36 (2008).

    CAS  Google Scholar 

  90. Nakamura, M., Sawa, A., Fujioka, J., Kawasaki, M. & Tokura, Y. Interface band profiles of Mott-insulator/Nb:SrTiO3 heterojunctions as investigated by optical spectroscopy. Phys. Rev. B 82, 201101 (2010).

    Google Scholar 

  91. Matsubara, M. et al. Photoinduced switching between charge and orbital ordered insulator and ferromagnetic metal in perovskite manganites. Phys. Rev. B 77, 094410 (2008).

    Google Scholar 

  92. Kim, B. J. et al. Novel Jeff=1/2 Mott state induced by relativistic spin–orbit coupling in Sr2IrO4 . Phys. Rev. Lett. 101, 076402 (2008).

    CAS  Google Scholar 

  93. Datta, S. & Das B. Electronic analog of the electro-optic modulator. Appl. Phys. Lett. 56, 665–667 (1990).

    CAS  Google Scholar 

  94. Chernyshov, A. et al. Evidence for reversible control of magnetization in a ferromagnetic material by means of spin–orbit magnetic field. Nature Phys. 5, 656–659 (2009).

    CAS  Google Scholar 

  95. Miron, I. M. et al. Current-driven spin torque induced by the Rashba effect in a ferromagnetic metal layer. Nature Mater. 9, 230–234 (2010).

    Google Scholar 

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

    CAS  Google Scholar 

  97. Katsura, H., Nagaosa, N. & Balatsky, A. V. Spin current and magnetoelectric effect in noncollinear magnets. Phys. Rev. Lett. 95, 057205 (2005).

    Google Scholar 

  98. Onoda, M. & Nagaosa, N. Quantized anomalous Hall effect in two-dimensional ferromagnets: quantum Hall effect in metals. Phys. Rev. Lett. 90, 206601 (2003).

    Google Scholar 

  99. Hasan, M. Z. & Kane, C. L. Topological insulators. Rev. Mod. Phys. 82, 3045–3067 (2010).

    CAS  Google Scholar 

  100. Qi, X. L. & Zhang, S. C. Topological insulators and superconductors. Rev. Mod. Phys. 83, 1057–1110 (2011).

    CAS  Google Scholar 

  101. Xiao, D., Zhu, W., Ran, Y., Nagaosa, N. & Okamoto, S. Interface engineering of quantum Hall effects in digital transition-metal oxide heterostructures. Nature Commun. 2, 596 (2011).

    Google Scholar 

  102. Smadici, S. et al. Electronic reconstruction at SrMnO3–LaMnO3 superlattice interfaces. Phys. Rev. Lett. 99, 196404 (2007).

    Google Scholar 

  103. Logvenov, G., Gozar, A. & Bozovic, I. High-temperature superconductivity in a single copper-oxygen plane. Science 326, 699–702 (2009).

    CAS  Google Scholar 

  104. Smadici, S. et al. Superconducting transition at 38 K in insulating-overdoped La2CuO4 -La1.64Sr0.36CuO4 superlattices: evidence for interface electronic redistribution from resonant soft X-ray scattering. Phys. Rev. Lett. 102, 107004 (2009).

    CAS  Google Scholar 

  105. May, S. J. et al. Magnetically asymmetric interfaces in a (LaMnO3)/(SrMnO3) superlattice due to structural asymmetries. Phys. Rev. B 77, 174409 (2008).

    Google Scholar 

  106. Boris A. V. et al. Dimensionality control of electronic phase transitions in nickel-oxide superlattices. Science 332, 937–940 (2011).

    CAS  Google Scholar 

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Acknowledgements

This work was partly supported by the Japan Society for the Promotion of Science (JSPS) through its Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program). H.Y.H. acknowledges support from the Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515. B.K. acknowledges support by the German Science Foundation under collaborative Grant No. SFB/TRR80. N.N. acknowledges support by MEXT Grand-in-Aid No. 20740167, 19048008, 19048015, 21244053, and the Strategic International Cooperative Program (Joint Research Type) from the Japan Science and Technology Agency.

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Hwang, H., Iwasa, Y., Kawasaki, M. et al. Emergent phenomena at oxide interfaces. Nature Mater 11, 103–113 (2012). https://doi.org/10.1038/nmat3223

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