Magnetism and charge and spin transport in graphene nanostructures

石墨烯不仅是一种非常有趣的科学材料，而且可能是未来自旋电子学和纳米电子器件最有前途的候选者之一。由于它的电子结构，它表现出了有史以来最高的载流子迁移率，低的超精细相互作用和低的自旋-轨道耦合导致了较长的自旋扩散长度和自旋寿命。基于我们最近观测到的涡流层石墨烯的巨大迁移率(100.000 cm2/(Vs))，我们将研究其性质与厚度的关系，以揭示环境、主要的散射和电荷输运机制的影响，并确定这个多层体系的迁移率的极限。没有隧道势垒的优化的高效自旋注入将使我们能够获得巨大的扩散自旋流，我们将确定自旋弛豫机制，以最大化自旋扩散长度和自旋积累，以期利用自旋流来操纵磁化。最终的基于石墨烯的纳米结构是石墨烯纳米带，其中所谓的扶手椅和之字形边缘可以通过自下而上合成和单原子传输电子显微镜雕刻作为图案化后的原子结构精度进行定制。我们将研究这些原子完美结构中的关键特征电荷和自旋输运性质，如载流子迁移率、霍尔系数和自旋扩散长度。除了经典的输运外，我们还将探索这些纳米结构的令人兴奋的非传统性质：导致带隙和磁缺陷或边缘感应态的量子限制将使用不同宽度的纳米带的电迁移纳米带隙几何结构和定制的边缘几何形状来研究，以测试各种部分矛盾的理论预测。此外，通过使用可以在绝缘衬底上光刻接触的特殊功能纳米带，将首次分析这些有效的一维结构中的长距离量子输运。

Graphene is not only a very interesting material for science but also probably one of the most promising candidates for future spintronic and nano-electronic devices. Due to its electronic structure it exhibits the highest charge carrier mobilities ever measured and the low hyperfine interaction as well as the low spin-orbit coupling result in large spin diffusion lengths and spin lifetimes. Based on our recent observation of huge mobilities (100.000 cm²/(Vs)) in turbostratic graphene, we will study the thickness dependence of the properties to reveal the influence of the environment, the dominating scattering and charge transport mechanisms and ascertain the ultimate limit for mobilities in this multilayer-system. The optimized efficient spin injection without tunneling barriers will allow us to obtain large diffusive spin currents and we will ascertain the spin relaxation mechanisms to maximize the spin diffusion lengths and spin accumulation with a view of using spin currents to manipulate magnetisation.The ultimate graphene-based nanostructure are graphene nanoribbons where so-called armchair- and zigzag-edges can be tailored with atomistic structural precision using bottom-up synthesis and single atom transmission electron microscopy-based sculpting as post-patterning. We will study key characteristic charge and spin transport properties, such as the charge carrier mobility, Hall coefficient and spin diffusion length in these atomically perfect structures. In addition to classical transport, we will probe the exciting unconventional properties that have been predicted for these nano-structures: Quantum confinement leading to bandgaps and magnetic defect- or edge-induced states will be studied using electromigrated nano-gap geometries for nanoribbons with different widths and tailored edge geometries to test a variety of partly contradicting theoretical predictions. Furthermore by using specially functionalized nanoribbons that can be lithographically contacted on insulating substrates, the quantum transport over long distances in these effectively 1D structures will be analyzed for the first time.