Design and Characterization of Two-Dimensional Electron Gas with Strong Spin-Orbit Coupling Based on Transition Metal Oxides

随着人们对更快、更小的电子产品的要求，功耗、有限尺寸效应和其他几个因素的挑战严重限制了未来设备的小型化。利用电子自旋而不是电荷的自旋电子学已成为下一代电子学的候选之一。传统上，自旋电流是通过使用磁性材料产生的，这需要磁场来操纵其方向。为了显著降低功耗并结合多功能，使用电动手段来控制和操纵旋转是非常可取的。自旋霍尔效应是由于一种称为自旋轨道耦合的效应，可以在不使用磁性材料的情况下从电荷电流中产生自旋电流。这种效应的特征是自旋-电荷转换效率，它与材料中的自旋-轨道耦合强度成正比。最近的实验证明了在过渡金属氧化物界面的二维电子气体系统中具有前所未有的自旋-电荷转换效率。该项目旨在开发和研究在选定的金属氧化物界面上设计的具有非常大的自旋轨道耦合和高迁移率的新型二维电子气体。研究重点是了解与界面工程相关的基本量子现象，提高自旋电荷转换效率。该项目为研究生和本科生提供科学的培训。首席研究员还寻求延续这一传统，参与几个专门为招募和建议代表性不足的少数民族研究生的项目。rashba自旋轨道耦合是许多新兴现象的核心，自旋电子学一直在积极探索，因为它可以使电荷电流通过自旋霍尔效应产生自旋电流。最近在基于SrTiO3的界面二维（2D）电子气体中展示了前所未有的自旋-电荷转换效率，使氧化物界面处于自旋-轨道电子学的前沿。认为Rashba效应和高迁移率的综合因素导致了非常大的效应，超过了拓扑绝缘子的效应，尽管系统中的自旋轨道耦合强度并不大。本项目旨在从5d过渡金属氧化物中开发具有高迁移率和二维约束的具有大Rashba效应的电子气体，其自旋轨道耦合比SrTiO3 （3d电子）大得多，以实现更高的自旋电荷转换效率。此外，在5d金属氧化物的（111）取向中预测了新的磁性和拓扑相，并将对其进行研究。基于在KTaO3（001）基绝缘体界面上获得电子气体的初步结果，将通过材料工程在多种金属氧化物中开发和研究具有高迁移率的二维电子气体。量子输运测量将在低温和高磁场下进行，以探测能带结构、Rashba分裂和奇异相的细节。利用自旋霍尔效应、逆自旋霍尔效应和自旋扩散长度研究自旋电流的产生和检测。氧化电子气体中的自旋电荷相互转换可以在室温和栅极可调下工作，使其成为自旋轨道电子学中最有前途的材料之一。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technicalWith the demands for faster and smaller electronics, the challenge of power dissipation, finite size effects, and several other factors places a serious limit on the future device miniaturization. Spintronics, which utilizes the electron spins instead of charges, has emerged as one of the candidates for the future generation of electronics. Traditionally, spin current is generated by using magnetic materials, which requires a magnetic field to manipulate its orientation. To significantly reduce the power consumption and incorporating multi-functionality, using an electric mean to control and manipulate spins is highly desirable. Spin Hall effect, which is due to an effect called spin-orbit coupling, can generate spin current from the charge current without using magnetic materials. This effect is characterized by spin-charge conversion efficiency which scales with the spin-orbit coupling strength in a material. Recent experiments demonstrated an unprecedented efficiency of spin-charge conversion in a two-dimensional electron gas system at a transition metal oxide interface. This project aims to develop and study new two-dimensional electron gases engineered at selected metal oxide interfaces with very large spin-orbit coupling and high mobility. The research focuses on understanding the fundamental quantum phenomena in relationship to interface engineering as well as enhancing the spin-charge conversion efficiency. The project provides scientific training for graduate and undergraduate students. The principle investigator also seeks to continue the tradition to engage in several programs specifically for recruiting and advising under-represented minority graduate students.TechnicalRashba spin-orbit coupling is central to many emergent phenomena and has been actively explored for spintronics as it can enable the generation of spin current from a charge current through spin Hall effect. Recent demonstration of unprecedented efficiency in spin-charge conversion in a SrTiO3 based interface two-dimensional (2D) electron gas has put the oxide interfaces at the forefront for spin-orbitronics. It is believed that the combined factors of Rashba effect and high mobility has resulted in the very large effect, which exceeds that of topological insulators, even though the spin-orbit coupling strength is not large in the system. This project aims to develop high mobility and 2D confinement of the electron gases with large Rashba effect from 5d transition metal oxides with much larger spin-orbit coupling than that of SrTiO3 (3d electrons) to achieve larger spin charge conversion efficiency. Furthermore, novel magnetic and topological phases have been predicted in the (111) orientation of 5d metal oxides which will be studied. Based on the preliminary results of achieving electron gases at KTaO3 (001) based insulator interfaces, 2D electron gases with high mobility will be developed and studied in several metal oxides through materials engineering. Quantum transport measurements will be conducted at low temperature and high magnetic fields to probe the details of the band structures, Rashba splitting, and exotic phases. Spin current generation and detection using spin Hall and inverse spin Hall effect and spin diffusion length will be studied. Spin charge interconversion in oxide electron gases can work at room temperature and gate tunable, making it one of the most promising materials for spin-orbitronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.