Physics of Mott Semiconductors

该研究项目旨在发展莫特绝缘体的半导体物理学，这些绝缘体预计将成为下一代电子产品的关键元件。为了从实验上阐明“莫特半导体”中杂质态或界面态等半导体物理原理是如何被修改的，我们进行了以下主题的研究。1. STM/STS对Sr_3Ru_2O_7的局域光谱利用STM/STS研究了位于磁态和轨道态临界边缘的Sr_3Ru_2O_7中引入的锰杂质的影响。杂质的影响的长度尺度被发现达到几个纳米，由于强相关电子的屏蔽减少。我们还观察到低能区电子态密度谱的异常演化，这与变磁不稳定性有关.静电载流子掺杂引起的金属-绝缘体转变我们设计了有机栅绝缘体氧化物场效应晶体管。将此方法应用于钙钛矿型氧化物SrTiO_3的原型材料中，实现了静电载流子掺杂的绝缘体到金属的转变。在金属相中，载流子迁移率超过1000 cm ^2/Vs. 3。电阻式随机存取存储器（RRAM）被认为是下一代的界面器件。然而，阻变的机制仍有待阐明。通过制备二元过渡金属氧化物平面型器件并直接观察其界面，证实了脉冲电场诱导下导电细丝的形成，并发现在细丝与金属电极的界面处发生阻变。

This research project has aimed for the development of semiconductor physics of Mott insulators which are anticipated as key elements of next generation electronics. We have worked on the following subjects in order to clarify experimentally how the principles of semiconductor physics, such as impurity states or interfacial states, are modified in "Mott semiconductors".1.Local spectroscopy on Sr_3Ru_2O_7 by STM/STSThe effect of Mn impurities introduced into Sr_3Ru_2O_7, which is located on the verge of the magnetic and orbital state criticality, was investigated by STM/STS. The length scale of the influence of impurities was found to reach several nm due to the reduced screening of strongly correlated electrons. We also observed the anomalous evolution of electron density of states spectra at the low-energy region, which is related to the metamagnetic instability.2. Metal-insulator transition induced by electrostatic carrier dopingWe have designed oxide field-effect transistors with organic gate insulators. By applying this method to SrTiO_3, the prototype perovskite oxide, we have realized the insulator to metal transition by electrostatic carrier doping. In the metallic phase, the carrier mobility exceeds 1000 cm^2/Vs.3. Resistive switching memory in binary transition-metal oxides Resistive random access memory (RRAM) is expected as an interfacial device of next generation. However, the mechanism of the resistive switching remains to be elucidated. By fabricating planer-type devices with binary transition-metal oxides and directly observing the interfaces, we evidenced the formation of conducting filament induced by pulse electric fields, and also found that the resistive switching occurs at the interface between the filament and metal electrodes.