Fabrication of two-dimensional electron gas with high mobility in SrTiO_3 to develop novel quantum

本项目的目标是在SrTiO3中实现二维电子气。为此，制备异质结构和了解异质界面的电子结构是必不可少的。我们报告了与此目的相关的结果1。我们在SrTiO_3(100)衬底上沉积了LaAlO_3薄膜，并用电子能谱对其界面电子结构进行了研究。对于SRO终止的衬底，由极性不连续产生的空穴被氧空位补偿。这是消除了带偏移的结果，这也是从二氧化钛衬底产生的n型界面观察到的结果。我们通过测量结的性质，探索了钛酸锶与过渡金属氧化物界面的电子结构。结果，我们发现磁场在锰氧化物的界面处发生了化学势的移动，从而调节了结的性质。精确的分析揭示了电子隧穿在结性质中的重要性。用内光电子能谱观测到了在SrRuO_3/Nb：SrTiO_3界面上形成的肖特基势垒高度。结果表明，界面可用肖特基-莫特模型描述。我们发现，这种方法可以普遍适用于其他由过渡金属氧化物组成的界面。我们利用Mott绝缘体制作了量子阱结构，并对其电子态进行了探测。我们已经使用了钒酸镧。结果发现，由于X射线光电子能谱的电荷重构，我们发现在钒酸盐的顶层存在着不以体相形式存在的四价钒。此外，通过调整生长条件，形成了三价钒和五价钒的竞争相。我们还用电子能谱在相界上发现了四价钒。

This project is aimed at realizing a two-dimensional electron gas in SrTiO_3. For that purpose, it is essential to fabricate heterostructures and to understand electronic structures at the heterointerfaces. We report our results related to this purpose.1. We have deposited LaAlO_3 films on SrTiO_3(100) substrates and probed the interface electronic structure by EELS. For SrO-terminated substrates, holes generated by the polar discontinuity were compensated by oxygen vacancies. This is the result of the removal of the band offset, which was also observed for an n-type interface originating from TiO_2-terminated substrates.2. We have probed the interface electronic structure at an interface of strontium titanate and transition-metal oxides by measuring junction properties. As a result, we have found a chemical potential shift by magnetic field at the interface of manganite, which modulates the junction properties. Precise analysis has revealed the importance of electron tunneling in the junction properties.3. We have observed the Schottky barrier height formed at SrRuO_3/Nb : SrTiO_3 interface by internal photoemission spectroscopy. As a result, the interface can be described by the Schottky-Mott model. We have found that this method can be generally applicable to other interfaces composed of transition-metal oxides.4. We have fabricated a quantum well structure by a Mott insulator and probed the electronic states. We have used lanthanum vanadate. As a result, we have found the existence of tetravalent vanadium, which does not exist in a bulk form, at the top layer of the vanadate due to a charge reconstruction by x-ray photoemission spectroscopy. In addition, a competing phase of trivalent vanadium and pentavalent vanadium is formed by adjusting growth conditions. We have also found tetravalent vanadium at the phase boundary by EELS.