Physics of Mott Semiconductors

该研究项目旨在发展半导体物理的莫特绝缘体，预计将成为下一代电子产品的关键要素。为了从实验上阐明在“莫特半导体”中如何修改诸如杂质态或界面态等半导体物理原理，我们对以下主题进行了研究。STM/STS对Sr_3Ru_2O_7的局部光谱研究了Sr_3Ru_2O_7处于磁性和轨道临界态边缘时，Mn杂质对Sr_3Ru_2O_7的影响。由于减少了对强相关电子的筛选，杂质影响的长度尺度达到了几nm。我们还观察到低能区态谱电子密度的异常演化，这与变磁不稳定性有关。静电载流子掺杂引起的金属-绝缘子跃迁我们设计了带有有机栅绝缘子的氧化场效应晶体管。将该方法应用于SrTiO_3（钙钛矿氧化物原型）上，实现了静电载流子掺杂从绝缘体到金属的过渡。在金属相中，载流子迁移率超过1000 cm^2/Vs.3。电阻性随机存取存储器（RRAM）有望成为下一代的接口器件。然而，阻性开关的机制仍有待阐明。通过用二元过渡金属氧化物制作刨床型器件，并直接观察其界面，我们证实了脉冲电场诱导下导电灯丝的形成，并发现在灯丝与金属电极的界面处发生了电阻开关。

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.