Charge-Spin Conversions in Helical Metals and Chiral Materials

摘要：传统的半导体微电子技术仅利用电子电荷进行逻辑运算。已经证明，利用电子的自旋不仅可以提高性能，如大幅降低功耗，而且还可以产生基本的新功能，如非易失性和可重构逻辑。自旋半导体电子学的一个重要组成部分是在非磁性半导体中产生具有明确自旋方向的电子居群和电流，即自旋极化。该项目旨在通过纯电手段产生、控制和检测半导体中的极化自旋，在某些情况下甚至不使用任何磁性材料。一种方法是通过驱动电流通过拓扑绝缘体的表面，其中电子速度和自旋总是锁定在正交方向上；另一种是通过推动电子通过手性介质，这种介质可以是单层手性有机分子或具有固有手性晶体结构的无机材料。实际上，该研究可能导致无磁性材料自旋电子学器件的新范式。在基础层面上，它们为研究由于结构手性和电子相互作用导致的电荷-自旋转换的微观机制提供了理想的平台。该项目还展示了基础科学研究与技术开发的宝贵结合，为研究生在学术界和工业界的职业生涯做好准备。技术摘要：本项目旨在通过纯电手段，在某些情况下不使用任何磁性材料，产生、控制和检测半导体中的极化自旋。该项目有两个不同的研究重点，它们有一个共同的目标，即解决由于结构手性和电子相互作用导致的电荷-自旋转换的表现和微观机制。这两条研究路线的目标是在两种不同的系统中演示和理解电荷运动产生的自旋电流：i)表面状态在动量空间中表现出螺旋自旋纹理的3D强拓扑绝缘体，ii)在实空间中具有固有结构手性的材料。在第一个系统中，研究引入了光电流注入和拓扑表面态的相关表征，这为破译电流诱导自旋极化背后的微观机制和确定其器件应用潜力提供了很大的可能性。对手性材料的自旋过滤效应的研究旨在对手性介质中自旋相关输运产生基本的认识。这些物理手性结构的结果对拓扑材料中涌现自旋螺旋态的相关研究具有广泛的意义。实际上，该研究可能会带来概念上新的自旋注入和检测方法，为无磁性材料的自旋电子学器件平台奠定基础。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-technical Abstract:Conventional semiconductor microelectronics utilize only the charge of electrons for logic operations. It has been demonstrated that harnessing the spin of electrons can not only lead to enhanced performance such as dramatic reduction in power consumption but also produce fundamentally new functionalities such as nonvolatility and reconfigurable logics. An essential ingredient of spin-based semiconductor electronics is the creation of electron populations and currents with well-defined spin orientations, i.e., spin polarization, in a nonmagnetic semiconductor. This project aims to generate, control, and detect polarized spins in semiconductors through pure electrical means, and in some cases without even using any magnetic material. One way is by driving an electric current through the surface of a topological insulator, where the electron velocity and spin are always locked in orthogonal directions; the other is by pushing electrons through a chiral medium, which can be a monolayer of chiral organic molecules or inorganic materials with inherent chiral crystal structures. Practically, the research may lead to new paradigms of spintronics devices free of magnetic materials. At the fundamental level, they offer ideal platforms for studying microscopic mechanisms of charge-spin conversions due to structural chirality and electronic interactions. The project also presents an invaluable combination of basic science research and technology development, an effective venue for preparing graduate students for careers in academia and industry.Technical Abstract:This project is aimed at the generation, control, and detection of polarized spins in semiconductors through pure electrical means, and in some cases without using any magnetic material. The project has two distinct research thrusts, which share a common objective of addressing the manifestations and microscopic mechanisms of charge-spin conversions due to structural chirality and electronic interactions. The two lines of research specifically target demonstrating and understanding electrical generation of spin currents from charge motion in two different systems: i) 3D strong topological insulators whose surface states exhibit helical spin textures in momentum space and, ii) materials with intrinsic structural chirality in real space. In the first system, the research introduces photocurrent injection and correlated characterizations of the topological surface state, which offers high probability of deciphering the microscopic mechanism behind the current-induced spin polarization and determining its device application potentials. The study on the spin filtering effect of chiral materials is designed to produce fundamental insights on spin-dependent transport in the chiral media. The results from these physical chiral structures have broad implications in pertinent studies of emergent spin-helical states in topological materials. Practically, the research may lead to conceptually new methods of spin injection and detection, forming the basis for spintronics device platforms free of magnetic materials.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.