基于拓扑绝缘体的自旋电子学器件

Topological spintronics is an emerging discipline aiming at developing novel spintronic devices by utilizing the special properties of topological insulators (TIs). The surface states of 3D TIs possess a helical spin texture in which the spin and momentum are locked to each other. Due to the spin-momentum locking, spin-charge interconversion can be easily achieved in 3D TIs: A net spin polarization can be induced by passing a charge current through the surface, and similarly, a charge current can be generated by injecting spin-polarized electrons into the surface states. This peculiar property makes 3D TIs a promising platform for realizing the new generation of spintronic devices...The experimental studies on topological spintronics started a few years ago and currently are still at a preliminary stage. The charge-current-induced spin polarization has been observed in 3D TIs. However, there has been a considerable controversy over the polarity and origin of the detected spin signals. Furthermore, many novel spintronic devices that has been proposed theoretically still remain to be realized. This project aims at investigating the aforementioned issues with spintronic devices based on 3D TIs. To be specific, we plan to (1) clarify the origin of the different types of spin signals observed in previous experiments by controlling the band bending of the TI sample beneath the ferromagnetic contacts and (2) experimentally realize the novel spin valve device proposed by Prof. Supriy Datta.

拓扑自旋电子学是利用拓扑绝缘体实现自旋电子器件的一个新兴研究方向。由于拓扑绝缘体的表面态电子具有“自旋-动量”锁定的特性，当电流从表面流过时，会在表面产生自旋极化；反之，当自旋极化的电子从外部注入拓扑绝缘体表面时，则会在表面产生电流。利用这一特性，可以便捷地实现电荷和自旋的相互转化。因此，拓扑绝缘体为发展新一代自旋电子器件提供了可靠的实验平台。.有关拓扑自旋电子学的实验研究目前尚处在起步阶段。人们虽然已经在拓扑绝缘体中观测到了电流引发的自旋极化，但对自旋信号的极性和来源还存在诸多争议；此外，许多器件的理论设计方案也还有待实验实现。本项目旨在从器件研究的角度探究上述问题的解决方式。具体而言，我们计划制备基于三维拓扑绝缘体的自旋电子器件，并研究以下内容：（1） 通过控制拓扑绝缘体在铁磁隧道结下方的能带弯曲，厘清不同自旋信号的物理来源。（2）在实验上实现基于拓扑绝缘体的新型自旋阀器件。

本项目的研究内容是基于拓扑绝缘体的自旋电子器件。近年来，研究人员意识到，除了拓扑绝缘体之外，除拓扑绝缘体外，拓扑半金属也具有非平庸的、能够产生非平衡自旋极化的表面电子态，因而也可以用于制备拓扑自旋电子器件。基于这一认识，我们对这一课题进行了适度的扩展，将研究范围扩展至包含拓扑晶体绝缘体和拓扑半金属在内。另外，在研究过程中，我们发现先前选定的技术路线不够可行，因此对其进行了适当的调整。..具体而言，本项目取得的主要成果如下：（1）制备了基于Sn掺杂的拓扑绝缘体BiSbTeSe2的自旋电子器件。得益于样品优良的体绝缘性质及较低的载流子浓度，我们在室温下实现了大于1欧姆的自旋电阻，器件的性能优于文献中对同类器件的报导。（2）利用磁控溅射制备了拓扑晶体绝缘体SnTe的多晶薄膜，优化了薄膜的退火条件，对薄膜的电子输运性质进行了系统的研究。同时，尝试制备了基于拓扑晶体绝缘体SnTe的多晶薄膜的自旋电子器件。（3）对拓扑半金属NbTe2纳米薄片的电输运性质进行了系统性的研究，对NbTe2中非饱和线性磁电阻的成因给出了全新的解释，为未来制备基于拓扑半金属NbTe2的自旋电子器件做好了准备。未来我们仍将在上述领域开展进一步的工作。