高能量光导率揭示的 LaAlO3/SrTiO3 中电荷转移和再分布的机制。

Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity.

机构信息

1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore.

1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore.

出版信息

Nat Commun. 2014 Apr 14;5:3663. doi: 10.1038/ncomms4663.

DOI:10.1038/ncomms4663

PMID:24728209

Abstract

In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e(-) from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥ 4 unit cells of LaAlO3) there is indeed a ~0.5e(-) transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤ 3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e(-) is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.

摘要

在凝聚态物理中，两种不同绝缘体之间的准二维电子气，即极性 LaAlO3 与非极性 SrTiO3（LaAlO3/SrTiO3）的界面，是一个引人注目的惊人发现。这种现象与 LaAlO3 薄膜的厚度有关，可以用极化崩溃模型来解释，该模型预计 LaAlO3 薄膜中的 0.5e(-)电荷会转移到 LaAlO3/SrTiO3 界面。在这里，我们通过研究宽能区（0.5-35 eV）的光学电导率，发现对于导电样品（≥4 个 LaAlO3 单元），确实有~~0.5e(-)的电荷从 LaAlO3 转移到 LaAlO3/SrTiO3 界面，这表明在绝缘样品（≤3 个 LaAlO3 单元）中，在极性 LaAlO3 亚层（从 AlO2 到 LaO）内发生了高达~~0.5e(-)的电荷再分布，而没有电荷转移到界面。因此，我们的结果揭示了绝缘和导电 LaAlO3/SrTiO3 界面中极化崩溃补偿的不同机制。