NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore.
Nat Commun. 2013;4:1838. doi: 10.1038/ncomms2804.
The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO₃/SrTiO₃, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO₃ and (110)-oriented SrTiO₃, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO₃/SrTiO₃ interface prepared on (110)-oriented SrTiO₃, with a LaAlO₃-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO₂/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.
在两种绝缘复杂氧化物（特别是 LaAlO3/SrTiO3）之间观察到高迁移率二维电子气，增强了氧化物在电子学方面的潜力。这种导电性的出现被认为是由极化不连续性驱动的，导致电子重构。在这种情况下，晶体取向起着重要的作用，例如，在 LaAlO3 和（110）取向的 SrTiO3 之间的界面，就不应该存在极化不连续性，因此不会有导电性。在这里，我们报告了在（110）取向的 SrTiO3 上制备的 LaAlO3/SrTiO3 界面上观察到的出乎意料的导电性，其具有 LaAlO3 层厚度依赖性的金属-绝缘体转变。密度泛函理论计算表明，通过考虑能量有利的（110）界面结构，即翘曲的 TiO2/LaO，仍然存在极化不连续性，电子重构，从而仍然有可能在这个（110）界面上产生导电性。进一步发现，导电性在不同的晶体学方向上具有强烈的各向异性，具有各向异性超导性和磁性的潜力，从而导致可能的新物理和应用。
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