Spin transport; quantum transport; new materials; topological insulators

该项目的主要目标是利用倒置的器件结构探索双基拓扑绝缘体（TI）表面态的自旋极化，其中TI从底部而不是从顶部表面进行电接触。这种特殊的制造方法能够显著改善ti -电极界面，从而增强器件性能。我们建议使用两种器件：(1)在第一组器件中，我们机械地将TI/hBN异质结构转移到Co/MgO和Au电极上，这些电极在Si++/SiO2晶圆上预印。铁磁Co/MgO电极作为表面自旋极化的自旋敏感探测器，探测ti -MgO/Co界面的自旋积累。我们的器件可以在不干扰条纹场的情况下探测钛表面自旋极化，条纹场可能会掩盖测量的自旋电压。(2)在第二组器件中，我们的目标是将TI的表面自旋极化转化为自旋电流，并从TI表面注入相邻的石墨烯层。这种自旋电流应该通过使用额外的Co/MgO电极的自旋阀测量来探测远离TI材料的非局部。在这些装置中，我们期望在ti -石墨烯界面上探测邻近诱导的自旋轨道耦合。我们还建议使用光电流测量作为TI表面极化的自旋灵敏探头。虽然之前的几个光电流实验只是通过测量偏振依赖性的对称性分析间接证明了自旋贡献，但我们的目标是将ti -石墨烯界面的光电流激发与自旋敏感的电读出结合起来。

The main goal of this project is to explore the spin polarization of surface states in Bi-based topological insulators (TI) using an inverted device structure where the TI is electrically contacted from the bottom rather than from the top surface. This special fabrication method has the ability to significantly improve the TI-to-electrode interface yielding enhanced device performances. We suggest using two kinds of devices: (1) In the first set of devices we mechanically transfer a TI/hBN heterostructure onto Co/MgO and Au electrodes which were prepatterned on a Si++/SiO2 wafer. The ferromagnetic Co/MgO electrode acts as a spin-sensitive detector of the surface spin polarization which probes the spin accumulation at the TI-to-MgO/Co interface. Our devices offer to explore the TI surface spin polarization without disturbing fringe fields which may mask the measured spin voltages. (2) In the second set of devices, we aim to convert the surface spin polarization of the TI into a spin current which we inject from the TI surface into an adjacent graphene layer. This spin current shall be probed away from the TI material non-locally by spin-valve measurements using additional Co/MgO electrodes. In these devices, we expect to probe proximity-induced spin-orbit coupling at the TI-tographene interface. We also propose to use photo current measurements as spin sensitive probes of the TI surface polarization. While several previous photo current experiments only indirectly prove spin contributions by symmetry analysis of the measured polarization dependence, we aim to combine photo current excitation at the TI-to-graphene interface with spin-sensitive electrical read-out.