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Formation of two-dimensional small polarons at the conducting LaAlO_3/SrTiO_3 interface

机译：在导电LaAlO_3 / SrTiO_3界面处形成二维小极化子

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摘要

A long-lasting puzzle of the conducting LaAlO3/SrTiO3 (LAO/STO) interface is that the excess electron density counted in the transport measurements is much less than 0.5 electrons per unit cell as predicted by the polar catastrophe model. In this study, via first-principles calculations, we show that the excess electrons at the LAO/STO interface favor the formation of small polarons. These electrons interact strongly with the interfacial Ti ions, forming localized midgap states, which make an insignificant contribution to the conductivity. We also find that the interaction between the neighboring spin-polarized small polarons is weak and does not lead to long-range magnetic ordering. Compared with bulk STO, the formation of the polarons is more favorable at the LAO/STO interface, which is ascribed to the reduced symmetry of the crystal field and the increased lattice distortion. Our results suggest that a large number of the excess electrons at the LAO/STO interface are localized in the form of small polarons, which can partially explain the unexpected fewer electrons in the transport measurements, and also shed light on understanding various properties of other complex perovskite oxide interfaces.
机译：导电LaAlO3 / SrTiO3（LAO / STO）界面的一个长期难题是，在传输测量中计算出的过量电子密度远小于极地突变模型所预测的每单位电池0.5个电子。在这项研究中，通过第一性原理计算，我们显示了LAO / STO界面处的多余电子有利于小极化子的形成。这些电子与界面Ti离子强烈相互作用，形成局部中能隙态，这对电导率的贡献不大。我们还发现，相邻的自旋极化小极化子之间的相互作用很弱，并且不会导致长距离磁排序。与本体STO相比，在LAO / STO界面上极化子的形成更为有利，这归因于晶体场对称性的降低和晶格畸变的增加。我们的结果表明，LAO / STO界面上的大量多余电子以小极化子的形式定位，这可以部分解释传输测量中意料不到的电子数量减少，也有助于理解其他复合物的各种性质钙钛矿氧化物界面。

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  • 来源
    《Physical review》 |2019年第8期|085413.1-085413.7|共7页
  • 作者

    Kong Weilong; Zhou Jun; Luo Yong Zheng; Yang Tong; Wang Shijie; Chen Jingsheng; Rusydi Andrivo; Feng Yuan Ping; Yang Ming;

  • 作者单位

    Natl Univ Singapore Dept Phys Singapore 117542 Singapore;

    ASTAR Inst Mat Res & Engn 2 Fusionopolis Way Singapore 138634 Singapore;

    Natl Univ Singapore Dept Mat Sci & Engn Singapore 117575 Singapore;

    Natl Univ Singapore Dept Phys Singapore 117542 Singapore|Natl Univ Singapore NUSNNI NanoCore Singapore 117411 Singapore|Natl Univ Singapore Singapore Synchrotron Light Source Singapore 117603 Singapore;

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