Current induced spin polarization in 3D topological insulator thin films

本计画的目的是在三维拓扑绝缘体薄膜的表面态中，以实验的方式验证电流感生的自旋极化。所需的自旋检测能力应在铁磁金属接触的帮助下实现，铁磁金属接触通过用作隧道势垒的石墨烯薄层与拓扑绝缘体分离，以确保合适的自旋阻抗匹配条件。此外，石墨烯被设计成化学稳定界面，从而能够保留交叉载流子的自旋信息。设想了两种不同的策略，以避免由于相对表面上的载流子的相反手性而导致的自旋极化的抵消。在第一种方法中，计划在其中一个表面上涂上一层磁性薄膜，从而打开一个能隙。第二种策略涉及背栅和顶栅的实现，其使得能够分别将两个表面独立地调谐到双折射型制度中。对于后者的任务，锑掺杂的TI纳米片（BixSb 1-x）2 Te 3表现出强烈抑制体电子浓度将通过气-固生长方法制备。详细研究磁场依赖的开关行为的设备作为温度的函数，石墨烯层的厚度，以及栅极控制的载流子浓度将提供有关拓扑绝缘体的自旋产生能力的有价值的信息。

This project aims to experimentally demonstrate current-induced spin polarization within the surface states of three-dimensional topological insulator thin films. The required spin detection capability shall be implemented with the aid of a ferromagnetic metal contact, which is separated from the topological insulator by a thin layer of graphene serving as a tunnel barrier that ensures suitable spin-impedance matching conditions. In addition, the graphene is devised to chemically stabilize the interface, thus enabling to preserve the spin information of the crossing carriers. Two different strategies are envisioned in order to avoid cancelation of the spin polarization due to the opposite chiralities of the carriers on the opposite surfaces. In the first approach, it is planned to open an energy gap in one of the surfaces by coating it with an ultrathin magnetic film. The second strategy involves the implementation of a back and top gate that enable tuning the two surfaces independently into the nand p-type regime, respectively. For the latter task, antimony-doped TI nanosheets (BixSb1-x)2Te3 exhibiting a strongly suppressed bulk electron concentration shall be prepared by a vapor-solid growth method. Detailed studies of the magnetic field-dependent switching behavior of the devices as a function of temperature, the thickness of the graphene layer, as well as the gate-controlled carrier concentration shall provide valuable information regarding the spin generating capability of topological insulators.