RS Fellow - EPSRC grant (2014): Mitigating spin-current relaxation in spin-orbit coupled graphene: towards spin current routing in 2D carbon

石墨烯凭借其迷人的电子特性和在柔性电子和太阳能电池等多种领域的创新应用的巨大潜力，开启了固态物理学的新篇章。石墨烯研究的一个方面目前吸引了很多关注，那就是控制电子的一种基本性质，即自旋。这表明电子总是处于两种可能状态中的一种，要么是“上”，要么是“下”，这意味着电子本身可以为二进制逻辑位（“0”或“1”）提供基础。与目前的充电技术相比，基于这种概念的设备有望以更低的能耗实现更快的处理速度。然而，基于自旋的晶体管的实际实现需要新兴的纳米材料来有效地控制电荷电流的自旋状态。石墨烯是最有希望的候选者之一，因为它完全由一个只有一个原子厚的二维碳网络组成。这一特性导致了极高的表面灵敏度，并有可能非常精确地定制电子、化学和磁性，例如，通过吸附原子物种（附着原子）。我们最近预测，导致石墨烯中自旋轨道耦合局部增强的adatoms可以在没有磁场的情况下驱动宏观自旋电流的形成，这种现象被称为自旋霍尔效应。一个突出的问题是关于主要的自旋弛豫机制，这些机制限制了自旋霍尔效应在修饰石墨烯中产生的自旋信号的寿命。该理论项目将采用广泛的方法，结合分析工具和具有数十亿原子的全量子输运模拟的新方法，揭示在相关时间尺度上结合鲁棒自旋电流产生和自旋相干性的adatom装饰。后者是实现探索最近发现的自旋霍尔效应所必需的自旋逻辑函数的关键一步。

Graphene has opened a new chapter in solid-state physics due its fascinating electronic properties and high potential for innovative applications in domains as diverse as flexible electronics and solar cells. One aspect of graphene research that is currently attracting much attention is in the control of a fundamental property of electrons known as spin. This dictates that an electron is always in one of two possible states, either 'up' or 'down', meaning that the electron itself could provide the basis for a binary logic bit ('0' or '1'). Devices based on such a concept promise faster processing speeds with less energy consumption than current charge-based technologies. However, the practical realisation of spin-based transistors awaits emergent nanomaterials enabling efficient manipulation of the spin state of charge currents. Graphene is one of the most promising candidates due to the fact that it entirely consists of a 2D network of carbon that is only one atom thick. This feature leads to extreme surface sensitivity and the possibility to very precisely tailor electronic, chemical, and magnetic properties through, for example, adsorption of atomic species (adatoms). We have recently predicted that adatoms leading to local enhancement of the spin-orbit coupling in graphene can drive the formation of macroscopic spin currents in the absence of magnetic fields, a phenomenon known as the spin Hall effect. An outstanding question is concerned with the main spin relaxation mechanisms that limit the lifetimes of spin signals generated through the spin Hall effect in adatom-decorated graphene. This theoretical project will employ a broad scope approach, combining analytical tools and a novel method for fully quantum transport simulations with billions of atoms, to uncover adatom decorations incorporating both robust spin current generation and spin coherence over relevant time scales. The latter is a crucial step towards the implementation of spin logic functions necessary to explore the recently discovered spin Hall effect.