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

随着对更快、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的器件小型化。自旋电子学利用电子自旋而不是电荷，已经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，这需要一个磁场来控制其取向。为了显著降低功耗并整合多功能，使用电子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，它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，它随材料中自旋-轨道耦合强度的变化而变化。最近的实验表明，在过渡金属氧化物界面的二维电子气系统中，自旋-电荷转换的效率是前所未有的。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的二维电子气体。这项研究的重点是了解与界面工程相关的基本量子现象，以及提高自旋-电荷转换效率。该项目为研究生和本科生提供科学培训。这位首席研究员还试图延续这一传统，专门从事几个项目，专门招收和建议未被充分代表的少数族裔研究生。技术Rashba自旋-轨道耦合是许多紧急现象的核心，并已被积极探索用于自旋电子学，因为它可以通过自旋霍尔效应从电荷电流中产生自旋流。最近的研究表明，在基于钛酸锶的界面二维电子气中，自旋-电荷转换的效率是前所未有的，这使得氧化物界面处于自旋-轨道电子学的前沿。尽管系统的自旋-轨道耦合强度不大，但Rashba效应和高迁移率的综合因素导致了很大的影响，超过了拓扑绝缘体的影响。这个项目的目的是开发具有大Rashba效应的电子气的高迁移率和2D限制，从5d的过渡金属氧化物中获得比SrTiO_3(3D电子)更大的自旋-轨道耦合，以获得更高的自旋电荷转换效率。此外，还预测了将要研究的5d金属氧化物(111)晶面上的新的磁性相和拓扑相。基于在KTaO_3(001)基绝缘体界面上实现电子气的初步结果，将通过材料工程的方法在多种金属氧化物中开发和研究高迁移率的2D电子气。量子输运测量将在低温和高磁场下进行，以探测能带结构、拉什巴分裂和奇异相的细节。将研究利用自旋霍尔效应和逆自旋霍尔效应以及自旋扩散长度产生和检测自旋流。氧化物电子气中的自旋电荷相互转换可以在室温下工作，栅极可调，使其成为最有希望用于自旋轨道电子学的材料之一。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.