Spin properties of Graphene

在该项目的第一部分中，已经确定了可能的磁性缺陷结构的光谱特征，包括石墨烯锯齿形边缘处的边缘态和几种类型的空位排列中的局域态。这些状态现在应该被证明是磁起源，即我们将探测的边缘状态和局域状态的磁性在空缺的静态自旋极化扫描隧道显微镜测量，以及通过探测动态进动的缺陷状态在磁场中的局部尺度上。对于后者，我们将利用隧道电流的噪声谱，推测其在局部自旋的进动频率处显示峰值。对于该项目的第二部分，我们使用MgO作为自旋注入和检测的势垒材料，在单层和双层石墨烯中进行了系统的自旋输运研究。双层石墨烯中占主导地位的自旋散射机制被证明是D 'yakanov-Perel类型，使得在具有最低载流子迁移率的样品中观察到最长的自旋弛豫时间。我们已经观察到自旋弛豫时间高达2 ns，这是一个数量级长于任何值以前报道的单层石墨烯。在接下来的时间里，我们将继续进行时间分辨的自旋输运测量，以获得有关自旋退相干的信息。因此，我们将通过改变衬底、栅极氧化物和制备工艺来提高跨阻，并控制石墨烯的迁移率。最后，我们将结合联合收割机的专业知识，这两个部分的项目，以探讨时间分辨自旋注入在本地规模。

In the first part of the project, spectroscopic features of probably magnetic defect structures have been identified including the edge state at a zig-zag edge of graphene and localized states in several types of vacancy arrangements. These states should now be proven to be of magnetic origin, i.e. we will probe the magnetic properties of edge states and localized states at vacancies by static spin-polarized scanning tunnelling microscopy measurements as well as by probing the dynamic precession of defect states in a magnetic field on the local scale. For the latter, we will take advantage on the noise spectrum of the tunnelling current presumably showing peaks at the precession frequency of a local spin. For the second part of the project, we have performed systematic spin transport studies in single and bilayer graphene using MgO as a barrier material for spin injection and detection. The dominant spin scattering mechanism in bilayer graphene is shown to be of D’yakanov-Perel type such that the longest spin relaxation time is observed in samples with the lowest carrier mobility. We have observed spin relaxation times of up to 2 ns, which are an order of magnitude longer than any values previously reported for single layer graphene. Within the next period, we will, proceed towards time-resolved spin transport measurements in order to obtain information about spin decoherence. Therefore, we will improve the trans-impedance and we will control the graphene mobility by varying substrate, gate oxide and preparation processes. Finally, we will combine the expertise of both parts of the project in order to probe the time-resolved spin injection on the local scale.