Novel device concepts for generating spin currents in graphene

该项目的最终目标是揭示单层和多层石墨烯的固有自旋输运性质。石墨烯是碳原子的二维晶体，是一种很有前途的材料，具有很长的自旋扩散长度和很长的电子自旋寿命，这两个都是先进自旋电子器件的关键先决条件。由于这种材料仅由表面原子组成，因此需要特别的注意和技术知识来处理其内在性质。为了应对这一挑战，我们首先建议用六方氮化硼从上下两面封装石墨烯，以最佳地保护其免受环境条件以及湿化学品和溶剂的影响。在这种方法中，与石墨烯的电接触应通过石墨烯片的外层碳原子建立。我们期望这种方法将使我们能够揭示石墨烯的固有自旋散射机制。由于它们的高载流子迁移率，这些结构也使研究弹道自旋输运现象成为可能，此外还提供了研究边对自旋输运的作用。其次，我们的目标是通过抑制自下而上非局部自旋阀器件中氧化势垒中导电针孔的形成来改善自旋注入和检测势垒，其中石墨烯层被机械转移到预定义的Co/MgO电极上。第三，我们建议探索在不使用外磁场的情况下控制注入自旋电流极化方向的方法。我们将使用表现出强自旋霍尔效应的金属作为电极材料，目的是通过邻近的非局域铁磁探测器探测注入的自旋极化来证明石墨烯中的电自旋注入。

The ultimate goal of this project is to uncover the intrinsic spin transport properties in single and in few layer graphene. Graphene, a two-dimensional crystal of carbon atoms, is a promising material for exhibiting very long spin diffusion lengths and long electron spin lifetimes, both crucial prerequisites for advanced spintronic devices. As this material only consists of surface atoms particular care and technological knowledge will be needed for addressing its intrinsic properties. To tackle this challenge, we first suggest encapsulating graphene by hexagonal boron nitride from both the top and the bottom sides to allow for best protection against ambient conditions as well as wet chemicals and solvents. In this approach, the electrical contact to graphene shall be established through the outer carbon atoms of the graphene sheet. We expect that this way will allow us to unveil intrinsic spin scattering mechanisms in graphene. Thanks to their high carrier mobility, these structures also enable to study ballistic spin transport phenomena and additionally offer to study the role of edges on spin transport. Secondly, we aim at improving the spin injection and detection barriers by suppressing the formation of conducting pinholes in the oxide barriers in bottom-up non-local spin-valve devices where the graphene layer is mechanically transferred onto predefined Co/MgO electrodes. Thirdly, we suggest exploring methods for controlling the polarization direction of the injected spin current without the need of using external magnetic fields. As electrode material we will use metals which show a strong spin Hall effect with the goal to demonstrate electrical spin injection into graphene by probing the injected spin polarization by neighboring non-local ferromagnetic detectors.