Spin-dependent transport and thermoelectric phenomena in multi-band systems

在过去的二十年里，金属和半导体领域的自旋电子学一直是智力挑战的持续来源。在这个场中，人们可以大致区分两种状态：一种是自旋-轨道耦合较弱并起微扰作用的状态，另一种是自旋-轨道耦合较强的状态。后一种制度在基本层面上仍然是理论上最困难的制度之一。该奖项支持理论和计算研究和教育，以研究具有强自旋-轨道耦合的复杂多波段系统中的自旋相关输运和热电特性。PI将专注于四个研究重点，这些研究主要集中在基础物理问题上，这些问题主要是由无法解释的实验现象学引起的：1)多输运体制中的异常霍尔效应。PI将分析和数值研究在绝缘状态下观察到的异常霍尔效应的现象学尺度的起源，以及金属状态的拓扑性质如何随着无序度的增加而变化。2)强自旋轨道耦合下的自旋动力学和自旋弛豫。PI将研究最近的光学实验，证明在该体系中独特的自旋动力学，通过非平衡输运技术探索这些动力学，并将它们与该体系中的自旋积累和自旋霍尔效应的新电测量联系起来，其中自旋轨道耦合可以系统地调谐。3)拓扑热电材料与自旋相关热电效应。PI将探索与位错中一维保护态相连的拓扑绝缘体的热力学性质，以及这些材料中的其他自旋热电输运现象。主要的重点将是找到方案和安排，其中热电效率可以调整到高于目前实现的大块材料值。4)稀释磁性半导体的局部化效应。PI将研究最近的实验，这些实验似乎表明费米表面在这些系统中具有混合特征，并探索强无序和自旋轨道耦合对该区域附近光学和输运现象的影响。在教育和推广方面，一些研究生和博士后研究人员将接受有关输运、光学和热电性质建模的各种分析和计算技术的培训。他们将与实验合作者密切合作，并有充分的机会访问他们并体验国际合作的努力。培训将帮助学生选择任何职业道路，无论是在学术界还是工业界。此外，PI将建立一个网站，其中包含以自旋电子学为重点的科学可视化教程，并基于开源代码Blender。还将开发一个关于自旋电荷输运的注释和基码的开放储存库。自旋电子学是一门新兴的技术，它不仅利用电子电荷，而且利用固态器件中电子的固有自旋。对于金属和半导体来说，在过去的二十年里，这一领域一直是智力挑战的持续来源。该奖项支持理论和计算研究以及教育，以研究电子如何被外部场（例如电池的电场）驱动通过某些材料。材料的输运性质反映了电子通过它的方式，这可能取决于它们的自旋（电子的固有性质）如何与材料相互作用。PI将研究复杂材料中自旋相关的输运性质，以及由热效应引起的电子性质，这些材料具有自旋与材料相互作用强的有趣性质。这是自旋电子学领域的一个令人兴奋和有趣的前沿。PI将专注于几个以基本物理问题为中心的研究重点，这些问题的动机要么是无法解释的实验现象学，要么是潜在的新变革方法，比如从热效应（热电）中有效获得电流的可能性，这种热电效应源于所谓的“拓扑绝缘体”的有趣特性，它只在表面或边界导电，而不是在内部导电。拟议的活动可能有助于开发热电效率和热管理的新范例，这些设备的大小约为人类头发的百万分之一。这些材料对能源使用效率至关重要，因为它们可以提供比现在的冷却器和冰箱更有效的热回收能源系统。在教育和推广方面，一些研究生和博士后研究人员将接受有关输运、光学和热电性质建模的各种分析和计算技术的培训。他们将与实验合作者密切合作，并有充分的机会访问他们并体验国际合作的努力。培训将帮助学生选择任何职业道路，无论是在学术界还是工业界。此外，PI将建立一个网站，其中包含以自旋电子学为重点的科学可视化教程，并基于开源代码。还将开发一个关于自旋电荷输运的注释和基码的开放储存库。

TECHNICAL SUMMARYThe field of spintronics, for both metals and semiconductors, has been a continuous source of intellectual challenges over the past two decades. Within this field one can broadly distinguish two regimes: one where the spin-orbit coupling is weak and acts as a perturbation, and another where the spin-orbit coupling is strong. The latter regime remains one of the most theoretically difficult at a fundamental level. This award supports theoretical and computational research and education to study spin dependent transport and thermoelectric properties in complex multiband systems with strong spin-orbit coupling. The PI will focus on four research thrusts centered on fundamental physics questions that are mostly motivated by unexplained experimental phenomenology:1) Anomalous Hall effects in multiple transport regimes. The PI will study analytically and numerically the origin of the phenomenological scaling of the anomalous Hall effect observed in the insulating regime and how the topological properties of the metallic regime transform as disorder increases.2) Spin dynamics and spin relaxation in the strong spin-orbit coupled regime. The PI will study recent optical experiments demonstrating unique spin dynamics in this regime, explore these dynamics through non-equilibrium transport techniques, and connect them to spin accumulation in this regime and new electrical measurements of the spin Hall effect where spin-orbit coupling can be tuned systematically.3) Topological thermoelectric materials and spin-dependent thermoelectric effects. The PI will explore the thermodynamic properties of topological insulators connected to the one-dimensional protected states in dislocations, as well as other spin thermoelectric transport phenomena in these materials. The primary focus will be to find schemes and arrangements in which thermoelectric efficiency can be tuned above bulk material values that are currently achieved.4) Localization effects in diluted magnetic semiconductors. The PI will study recent experiments that seem to indicate a mixed character of the Fermi surface in these systems, and explore the effects of strong disorder and spin-orbit coupling on optical and transport phenomena near this regime.On the educational and outreach front several graduate students and postdoctoral researchers will be trained in diverse analytical and computational techniques for the modeling of transport, optical and thermoelectric properties. They will work closely with experimental collaborators and have ample opportunities to visit them and experience an international collaboration effort. The training will help the students in any career path they may choose to take, whether it is in academia or industry. In addition, the PI will establish a website which incorporates tutorials on scientific visualization focused on spintronics and based on the open-source code Blender. An open repository of notes and base codes on spin-charge transport will be also developed.NON-TECHNICAL SUMMARYThe field of spintronics is an emerging technology that exploits not only the electronic charge but also the intrinsic spin of the electron in solid-state devices. For both metals and semiconductors, this field has been a continuous source of intellectual challenges over the past two decades. This award supports theoretical and computational research and education to study how electrons are driven through certain materials by external fields, for example the electric field of a battery. The resulting transport property of the material reflects the way electrons move through it which may depend on how their spin, an intrinsic property of the electron, interacts with the material. The PI will study spin dependent transport properties, and electronic properties induced by thermal effects, in complex materials with the interesting property that the interaction of the spin with the material is strong. This is an exciting and intriguing frontier in the field of spintronics. The PI will focus on several research thrusts centered on fundamental physics questions that are motivated by either unexplained experimental phenomenology or new potentially transformative approaches such as the possibility of efficiently obtaining electrical currents from thermal effects (thermoelectricity) that originate from intriguing properties of the so-called "topological insulators", which conduct electricity only on their surfaces or boundaries, rather than their interior. The proposed activities could potentially contribute to the development of new paradigms in thermoelectric efficiency and heat management in devices that are some one millionth size of the human hair. Such materials are of fundamental importance for energy usage efficiency as they could provide heat recovery energy systems that are more efficient than present day coolers and refrigerators. On the educational and outreach front several graduate students and postdoctoral researchers will be trained in diverse analytical and computational techniques for the modeling of transport, optical and thermoelectric properties. They will work closely with experimental collaborators and have ample opportunities to visit them and experience an international collaboration effort. The training will help the students in any career path they may choose to take, whether it is in academia or industry. In addition, the PI will establish a website which incorporates tutorials on scientific visualization focused on spintronics and based on an open-source code. An open repository of notes and base codes on spin-charge transport will be also developed.