Atomic-scale control of graphene magnetism using hydrogen atoms

石墨烯层中局部磁矩的选择性产生是实现石墨烯自旋电子学的关键要求，但仍然是一个主要的实验挑战。该项目的主要目标是通过吸附和进一步操纵石墨烯层上的单个氢原子，为这种可能性提供明确的实验证明。自2004年首次分离石墨烯以来，一直在追求将磁性纳入石墨烯的一长串性能。使用自旋作为额外的自由度将极大地促进石墨烯基器件的多功能性。一方面，石墨烯载流子预期的长自旋弛豫时间有利于自旋信息传递或自旋扩散现象。另一方面，石墨烯的磁性和电荷输运可以发生在相同的π带中，因此可以预见其在未来自旋电子学应用中的巨大潜力。从石墨烯研究的早期开始，所有的理论预测都一致认为石墨烯可以通过吸附单个氢原子随意磁化。然而，迄今为止，为这些非凡的预测提供直接证明的实验努力尚未成功，主要是因为很难同时提供氢化石墨烯样品的原子表征和控制。该项目将尝试克服这些挑战，甚至超越理论预期，在超高真空（UHV）环境中使用扫描隧道显微镜/光谱（STM/STS）作为主要实验技术。UHV-STM将使用具有非常不同功能的UHV-STM，这将提供广泛的温度范围（10mK-400K），磁场范围（0-14T）和衬底（从外延到可门控的剥落石墨烯）。我们的出发点是我们最近（未发表）的观察结果，即单个H原子在解耦石墨烯层上的吸附在费米能量上诱导了20meV的分离双峰，这很可能是由于自旋分裂（见2.2节中的图1）。这些初步结果还表明，可以使用STM尖端以原子精度操纵H原子，我们将利用这一点来定制选定石墨烯区域的磁性。该研究将在不同的衬底上进行石墨烯层。所产生的磁矩的演变将被系统地研究作为磁场、温度和电门的函数。这将使我们能够确认观察到的H诱导分裂态的磁性，了解由H原子集合产生的集体磁性，测试其温度稳定性，并通过外部电子门控来操纵磁性。最后，在石墨烯上以任何期望的几何形状排列氢原子的意想不到的可能性将使迄今为止仅限于纯理论框架的实验得以实现。

The selective generation of local magnetic moments in graphene layers is a key requirement to realize graphene spintronics, but still remains as a major experimental challenge. The main goal of this project is to provide an unambiguous experimental proof of this possibility by the adsorption and further manipulation of single H atoms on graphene layers. The incorporation of magnetism to the long list of graphene capabilities has been pursued since its first isolation in 2004. The use of spin as an additional degree of freedom would represent a tremendous boost to the versatility of graphene based devices. On one hand, spin information transfer or spin diffusion phenomena are favored by the expected long spin relaxation times of graphene carriers. On the other, graphene magnetism and charge transport can take place in the same pi bands and thus a major potential in future spintronics applications can be anticipated.Since the early days of graphene research, all theoretical predictions agree that graphene can be magnetized at will by the adsorption of single H atoms. However, experimental efforts to provide a direct proof of such remarkable predictions have so far been unsuccessful, mainly due to the difficulties of providing, at the same time, an atomistic characterization and control of the hydrogenated graphene samples. The project will try to overcome these challenges and to go even beyond theoretical expectations by using scanning tunnelling microscopy/spectroscopy (STM/STS) in ultrahigh-vacuum (UHV) environments as main experimental technique. UHV-STM with very different capabilities will be used, which will give access to a wide range of temperatures (10mK-400K), magnetic fields (0-14T), and substrates (from epitaxial to gatable exfoliated graphene).Our starting point is our recent (unpublished) observation that the adsorption of a single H atom on a decoupled graphene layer induces a 20meV separated double peeak at the Fermi energy, most probably due to spin-splitting (see fig 1 in section 2.2). These preliminary results also show that it is possible to use the STM tip to manipulate H atoms with atomic precision, which we will exploit to tailor the magnetism of selected graphene regions.The research will be performed for graphene layers on different substrates. The evolution of the generated magnetic moments will be systematically investigated as a function of magnetic field, temperature, and electric gating. This will enable us to confirm the magnetic nature of the observed H induced split-state, to understand the collective magnetic state generated by ensembles of H atoms, to test its temperature stability and to manipulate the magnetic properties by external electronic gating. Finally, the unexpected possibility to arrange H atoms on graphene with any desired geometry will enable the realization of experiments restricted so far to a pure theoretical framework.