Mapping Spin Polarisation in Quasi-One-Dimensional Channels

磁光克尔效应（MOKE）是由偏振光束（通常来自激光）与一组磁矩相互作用产生的。例如，铁磁材料（如铁或钴）中原子的自旋。具体地说，当光束从铁磁体的“自旋极化”表面反射时，光束的偏振会轻微旋转。角的大小取决于磁性的强度，称为克尔旋转。通过这种方式，可以直接测量材料的磁性，或者更一般地，如果光束可以精细聚焦，则可以直接测量纳米结构的自旋极化。我们建议使用MOKE来研究电子沿沿着量子线行进的自旋极化，量子线是由半导体异质结构中的金属表面栅极限定的窄通道（~ 500 nm）。量子线有许多有趣的特性，其中之一是它们可能允许完全自旋极化的传输，其中沿着量子线传输的电子的磁矩都是对齐的。这种性质，以及通过向金属表面栅极施加电压来控制它，对于那些希望使用量子线作为未来量子自旋电子器件的构建块的研究人员来说，是非常感兴趣的。然而，这种性质还没有被直接测量，只是从量子线的导电性质的非常仔细的测量中推断出来的。我们相信MOKE可以直接测量这些电子的自旋极化，这将提供推动固态量子自旋电子学领域发展所需的信息。一个类似的系统，具有很大的希望使用由石墨烯制成的通道，这有望使新一代极其可靠和节能的自旋电子器件成为可能。除了其优异的导电性能之外，如果石墨烯通道的边缘本身是自旋极化的并且因此是磁性的，则石墨烯希望提供对穿过它的电子的自旋极化的所需控制。目前还没有获得这种广泛预测和关键特性的实验证据，但我们相信，聚焦MOKE可以解决不确定性，并为石墨烯组件出现在超高效的未来电子设备中铺平道路。

The Magneto-Optic Kerr Effect (MOKE) results from the interaction of a polarised beam of light (usually from a laser) with a set of magnetic moments. For example, the spins of the atoms in a ferromagnetic material such as iron or cobalt. Specifically, the polarisation of the beam is rotated slightly as it reflects from the "spin polarised" surface of the ferromagnet. The size of the angle depends on the strength of the magnetism, and is known as the Kerr rotation. In this way, it is possible to obtain a direct measurement of the magnetism of a material, or more generally of the spin polarisation of a nanostructure if the beam can be finely focused. We propose to use MOKE to study the spin polarisation of electrons travelling along quantum wires, which are narrow channels (~500nm) defined by metallic surface gates in a semiconductor heterostructure. One of the many interesting properties of quantum wires is the possibility that they permit fully spin-polarised transport, in which the magnetic moments of the electrons travelling along the quantum wire are all aligned. This property, and its control by applying voltage to the metal surface gates is of great interest to researchers who want to use quantum wires as the building blocks of future quantum spintronic devices. However, this property has not been directly measured, only inferred from very careful measurements of the conducting properties of the quantum wire. We believe that MOKE could potentially measure the spin polarisation of these electrons directly, which would provide the information required to drive forward the field of solid-state quantum spintronics. A similar system which holds great promise uses channels made from graphene, which promises to make possible a new generation of extremely reliable and energy-efficient spintronic devices. Apart from its excellent conduction properties, graphene is hoped to provide the required control of spin polarisation of the electrons travelling through it if the edges of the graphene channel are themselves spin-polarised and therefore magnetic. No experimental evidence for this widely-predicted and crucial property has yet been obtained, but we believe that again, focused MOKE can resolve the uncertainty and pave the way for graphene-based components to appear in ultra-efficient future electronic devices.