Heusler结构自旋无能隙半导体的表/界面和自旋输运性质的研究

Spin gapless semiconductors (SGSs) are a new class of spintronic materials, which were theoretically proposed a few years ago, and several of them have been realized in experiment. The band structure of SGSs is semiconductor with an energy gap in one spin channel, and there is an zero gap in the other spin channel, which makes SGSs suitable for the design of spintronic devices with high performance and low energy consumption. However, the surface/interface effect may affect and even destroy the spin gapless semiconductortivity, and further affect the transport properties. Therefore, in this project, by combining recent experimental findings and theoretical predictions, we use the density functional theory combined with nonequilibrium Green's function to investigate the ternary and quaternary SGSs with Heusler structure: the surface stability, electronic structure and magnetism of SGSs; the interfacial stability, interfacial electronic states and spin transport properties such as spin filter effect, spin diode effect and tunnel magnetoresitance for the heterogeneous junctions and tunnel junctions of SGSs with semiconductors, and the formation mechanism and factors for these effects. These studies can present inportant material basis and scientific guidance for the experimental synthesis of thin films and multilayers of SGSs with Heusler structure, and for the applications of SGSs in spintronic devices.

自旋无能隙半导体(SGSs)是近几年才被提出并已有实验验证的一类新颖自旋电子学材料，其带结构在一个自旋方向具有一定的能隙，表现出半导体性，而另一个自旋方向具有零能隙，这使得SGSs非常适合用于设计高性能、低能耗的自旋电子器件。但表/界面效应可能会影响甚至破坏材料的自旋无能隙半导体性，进而影响其自旋输运性质。基于这些考虑，本项目主要利用密度泛函理论及其与非平衡态格林函数相结合的方法，结合最新的实验发现与理论预言，对新型三元和四元Heusler结构的SGSs开展以下研究：SGSs的表面稳定性、电子结构和磁性；SGSs与半导体构成的异质结和隧道结的界面稳定性、电子态以及自旋输运特性，如自旋过滤效应、自旋二极管效应和隧道磁阻等，并探讨这些效应产生的机理和影响因素。这些研究可以为Heusler结构的SGSs薄膜和多层膜的实验制备及其在自旋电子器件中的应用，提供重要材料基础和科学指导。

基于实验上合成的几个Heusler结构自旋无能隙半导体(薄膜)，我们设计了它们的异质结和磁隧道结，利用密度泛函理论与非平衡态格林函数相结合的方法，研究了它们的表/界面电子结构、磁性和自旋输运性质。发现了具有良好自旋过滤效应和自旋二极管效应的异质结CoFeMnSi/GaAs和Ti2MnAl/InAs,以及具有大隧道磁阻的磁隧道结CoFeMnSi/GaAs/CoFeMnSi和Ti2MnAl/InAs/Ti2MnAl。温差也可以在Ti2MnAl/InAs/Ti2MnAl中产生自旋过滤效应。产生这些自旋输运特性的起源可以从自旋极化的能带结构、输运谱和半导体理论中解释。此外，我们也在几个二维自旋电子器件中发现了上述输运现象，并预测了二维自旋无能隙半导体MXenes。这些研究可以为自旋无能隙半导体在自旋电子学和热自旋电子学中的应用提供理论指导。