Coupled Charge and Spin Transport in Topological Insulators

拓扑绝缘体是一类具有块状绝缘能隙和无间隙狄拉克锥边缘或表面态的新型量子材料。表面状态不受时间逆不变扰动的影响，如非磁性杂质、缺陷和重构。电荷与自旋唯一耦合，电荷电流产生自旋极化。由于表面态受到拓扑保护，并且动量态与自旋态耦合，因此可以减少散射并抑制噪声。在薄拓扑绝缘体中，可以通过栅极电压来控制rashba型自旋分裂。热电优值ZT随着薄膜厚度的减小而增大。总之，拓扑绝缘体在热电、电荷和自旋输运方面表现出了特殊的性能。这些材料和性能将从工程电子学的角度进行研究。利用这些特性的设备将被建造、建模和表征，这些设备的性能指标和基本限制将被确定。智力优势：本研究将同时进行实验和理论。该项目将(i)增加对高尺寸拓扑绝缘体材料的材料特性和物理过程的基本知识；（ii）构建、建模和表征利用拓扑绝缘特性进行计算、信号处理和传感的设备；（iii）确定这些器件的性能指标和基本限制，（iv）探索拓扑绝缘体在低耗散、低噪声互连中的使用；(5)发展电化学原子层沉积技术，制备拓扑绝缘体的少原子层薄膜。所有材料都将使用广泛的方法进行广泛的表征，包括原子力、扫描电子、透射电子显微镜、低能电子衍射、x射线光谱、俄歇光谱、电子探针微分析、微拉曼光谱、电学和热测量。实验测量结果将与器件模型和从头算进行比较，薄膜和纳米线材料的电子结构和振动模式的密度泛函理论计算。变革性概念包括使用低耗散，低噪声拓扑保护状态的拓扑绝缘体用于电子/自旋电子器件和低噪声，低功耗互连。更广泛的影响：成功的项目有可能导致利用拓扑绝缘体的低耗散，低噪声状态用于计算，通信和传感器的新技术。该项目的广泛影响影响了资助建议指南中描述的所有5个示例领域，其中在(i)扩大代表性不足群体的参与和（ii）通过本科生研究促进教学和培训方面尤为突出。加州大学河滨分校是一所西班牙裔服务机构，在加州大学所有校区中，西班牙裔学生人数最多。首席研究员和联合首席研究员在成功监督代表性不足的少数民族方面有着悠久的历史，他们曾担任国家科学基金会本科生纳米材料和器件研究经验网站的首席研究员和联合首席研究员，该网站专注于少数民族本科生参与研究，他们计划聘请少数民族研究生和本科生作为该项目的研究助理。

Topological insulators constitute a new class of quantum materials with bulk insulating energy gaps and gapless Dirac-cone edge or surface states. The surface states are protected against time-reversal-invariant perturbations such as non-magnetic impurities, defects, and reconstruction. The charge is uniquely coupled to the spin, and charge current creates spin polarization. Since the surface states are topologically protected, and the momentum states are coupled to spin states, scattering is reduced and noise is suppressed. In thin topological insulators, a Rashba-type spin splitting occurs which can be controlled by a gate voltage. The thermoelectric figure of merit, ZT, increases as film thickness is reduced. In summary, topological insulators have shown exceptional properties for thermoelectric, charge, and spin transport. These materials and properties will be investigated from an engineering electronics point of view. Devices that exploit these properties will be built, modeled and characterized, and the performance metrics and fundamental limits of such devices will be determined. Intellectual Merit: This investigation will be simultaneously carried out both experimentally and theoretically. The project will (i) add to the fundamental knowledge of the material properties and physical processes in highly-scaled topological insulator materials; (ii) build, model, and characterize devices that exploit topological insulating properties for computation, signal processing, and sensing; (iii) determine the performance metrics and the fundamental limitations of such devices, (iv) explore the use of topological insulators for low-dissipation, low-noise interconnects; and (v) develop the electrochemical atomic layer deposition technique to grow few-atomic-layer films of topological insulators. All materials will be extensively characterized using a wide range of methods including atomic force, scanning electron, and transmission electron microscopy, low energy electron diffraction, X-ray spectroscopy, Auger spectroscopy, electron probe micro-analysis, micro-Raman spectroscopy, electrical, and thermal measurements. Experimental measurements will be compared to device models and ab initio, density functional theory calculations of the electronic structure and vibrational modes of the thin film and nanowire materials. Transformative concepts include the use of low-dissipation, low noise topologically protected states of topological insulators for electronic / spintronic devices and low-noise, low-power interconnects.Broader Impact: The successful project has the potential to lead to new technologies that exploit the low-dissipation, low-noise states of topological insulators for computation, communications, and sensors. The broader impacts of this project affect all 5 example areas described within the grant proposal guide, and they are particularly strong in the areas of (i) broadening participation of underrepresented groups and (ii) promoting teaching and training through undergraduate research. The University of California Riverside is a Hispanic serving institution with the largest Hispanic student population among all of the University of California campuses. The principal investigator and co-principal investigator have a long history of successful supervision of underrepresented minorities, they served as principal investigator and co-principal investigator of the National Science Foundation Research Experience for Undergraduates Site for Nano Materials and Devices that focused on minority undergraduate student participation in research, and they plan to hire minority graduate and undergraduate students as research assistants for this project.