Current induced spin polarization in 3D topological insulator thin films

本项目旨在实验证明电流诱导的自旋极化在三维拓扑绝缘体薄膜的表面状态。所需的自旋检测能力应借助铁磁性金属触点来实现，该触点与拓扑绝缘体通过一层薄薄的石墨烯作为隧道屏障隔开，以确保合适的自旋阻抗匹配条件。此外，石墨烯设计用于化学稳定界面，从而能够保留交叉载流子的自旋信息。为了避免由于相对表面上载流子的相反手性而导致的自旋极化抵消，设想了两种不同的策略。在第一种方法中，计划在其中一个表面上涂上超薄磁性薄膜，从而打开一个能隙。第二种策略涉及到一个后栅极和顶栅极的实现，可以分别将两个表面独立地调整为nand p型。对于后一项任务，掺锑TI纳米片（BixSb1-x）2Te3显示出强烈抑制的体电子浓度，必须通过气固生长方法制备。详细研究器件的磁场依赖开关行为作为温度、石墨烯层厚度以及栅极控制载流子浓度的函数，将为拓扑绝缘体的自旋产生能力提供有价值的信息。

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.