受限Dirac材料磁性拓扑态的外场诱变及热电转换机理研究

Low-dimensional limited Dirac materials, such as silicene, germanene, phosphorene and molybdenum disulfide, have recently attracted much attention due to their simple structures and strong spin-orbit couplings. The electrically controllable band gap and the behavior of topological phase transition enable these materials to have great potential applications in low consumption devices. Although the structures and properties of these limited Dirac materials have been studied deeply, there still needs further exploring on the coexistence phenomenon of magnetism and topology as well as the problem of the corresponding thermoelectric conversion. More recent research has focused on the basic electronic properties and non-thermoelectric problems. This project aims to study the novel thermoelectric effects, driven by thermal gradient, in the process of topological quantum phase transitions for magnetic electrons in the limited Dirac materials, where the magnetic topological states can be induced by the synergy of substrate proximity effect, interlayer electric field, polarized light field and etc. Based on the characteristics of bulk and edge states with topological correlation, the highlight of this project is to study the manageable principles in caloritronic components, explore the thermoelectric conversion characteristics featured by Seebeck effect, Nernst effect and thermal magnetoresistance in relevance to spin and valley, and further reveal new rules under the modulations of structure, stacking form and quantum scale. This project is a further deepening research on the Dirac electronic properties and can provide necessary physical fundamentals for designing thermoelectric conversion devices with high performance and solving the problem of solid-state energy saving and environment protection.

硅烯、锗烯、磷烯和二硫化钼等低维受限Dirac材料，因结构简单并具有强自旋轨道耦合作用近年来备受关注，电学可调的能隙和拓扑相变行为使其在低功耗器件应用中极具潜力。在结构和物性上受限Dirac材料的研究已较为深入，但对磁性与拓扑的共存现象及其热电转换问题仍需进一步研究，目前更多的研究则集中在基本电子性质及非热电问题上。本项目拟研究受限Dirac材料磁性态电子在拓扑量子相变过程中热梯度场驱动所产生的新奇热电效应，其磁性拓扑态可通过衬底邻近效应、层间电场及偏振光场等协同作用进行诱变。基于拓扑关联的体态和边态特性，重点研究热电元器件易控机理，探索自旋、能谷关联的Seebeck效应、Nernst效应和热磁阻效应等对应的新机制，进一步揭示结构、堆积方式、量子尺寸等调变下系统展示的新规律。本项目是对Dirac电子性质研究的进一步深化，为设计高性能热电转换器件和解决固态节能环保问题提供必要的物理基础。

低维受限Dirac材料，因结构简单且易制备受到广泛关注，电控带隙及自旋或能谷关联的新奇物质相变使其在低功耗量子器件设计开发中颇具潜力。在结构及物性方面低维受限Dirac材料的研究已较为深入，但对磁性与拓扑共存现象、可能的热电转换问题等亟需进一步研究。在此背景下，本项目着重开展了四方面研究。（1）以硅烯、锗烯等重IV族拓扑材料为研究平台，在非常规电场触发和能谷协调机制下揭示受限Dirac材料系统中的巨热磁阻效应。此外，通过设计铁磁/反铁磁异质结系统首次从理论上实现了自旋二极管效应的单极-双极转变。（2）聚焦二维双层六角晶体系统这一研究对象，在非共振光、反铁磁及电控竞争机制下，我们发现了自旋-能谷极化的量子反常Hall相新拓扑相，其特征是一种自旋表现为量子能谷Hall效应，另一种自旋表现为量子反常Hall效应，在畴壁界面输运中表现出独特的自旋整流效应。另外，我们以双层溴化铬为例在铁磁绝缘体系统中通过静电doping破坏空间反演对称性实现了热驱动Dirac磁振子的拓扑能谷Hall效应和Seebeck效应等。（3）在近邻效应诱导双界面磁性机制下，我们设计了电控范德华反铁磁自旋阀新器件，研究了不同畴壁结构、外势垒对自旋阀输运的影响。同时，我们还探索了双界面Rashba问题，揭示空间反演对称性支持的层积反向Rashba自旋轨道耦合作用诱导的能带自旋手征性的消失现象及对称性破缺机制下能带拓扑性质的转变。进一步地，我们在前期研究基础上提出自旋电子学新分支概念“Layered Spintronics”，系统探索了双层系统多样化磁性态及对应的能带自旋劈裂。（4）在硼烯这一受限Dirac电子系统中，项目组成员开展了电子回反射、反常Klein隧穿、反常Andreev反射和Josephson效应等一系列新奇量子输运现象研究，充分展示了Dirac电子的可控性和独特性。因此，本项目研究是对Dirac电子性质研究的进一步深入，为设计高密度低功耗量子器件、解决固态节能环保问题等提供了必要的物理基础，为低维自旋电子学和能谷电子学发展提供了新思路和新方案。