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

本课题旨在在SrTiO_3中实现二维电子气体。为此，必须制造异质结构并了解异质界面上的电子结构。我们报告了与此目的相关的结果。我们在SrTiO_3（100）衬底上沉积了LaAlO_3薄膜，并用EELS对其界面电子结构进行了探测。对于sro末端衬底，由极性不连续产生的空穴由氧空位补偿。这是去除带偏移的结果，这也被观察到来自tio_2端基板的n型界面。我们通过测量钛酸锶与过渡金属氧化物界面的结性质来探测界面电子结构。结果表明，磁场在锰矿界面处产生了化学势位移，从而调节了锰矿界面的性质。精确的分析揭示了电子隧穿在结性能中的重要性。利用内部光电发射光谱法观察了SrRuO_3/Nb: SrTiO_3界面上形成的肖特基势垒高度。因此，该接口可以用Schottky-Mott模型来描述。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。我们利用莫特绝缘体制造了一个量子阱结构，并对其电子态进行了探测。我们用过钒酸镧。结果，通过x射线光电发射光谱的电荷重建，我们发现在钒酸盐的顶层存在四价钒，而不是以块状形式存在。另外，通过调节生长条件，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处发现了四价钒。

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.