Induced Spin Textures in van der Waals Heterostructures

石墨烯被发现后，人们很快意识到，石墨烯是自旋电子学的完美候选者，因为它具有高迁移率、低自旋轨道耦合和小的或没有超精细场。到目前为止，已经证明了自旋弛豫长度超过10微米。尽管结果与预期相去甚远，但所实现的价值已经使石墨烯成为传递自旋信息的理想平台。现阶段的关键问题是，如何利用石墨烯装置来实现自旋的操纵。在这项提议中，我们将研究通过在石墨烯中引入不同的自旋织构来增加对自旋的电磁控制的新途径。自旋织构是通过发展各种2D邻近异质结构来诱导的：首先，使用磁性绝缘体将在石墨烯和拓扑绝缘体中诱导交换相互作用。这将被异常的霍尔测量所证实。此外，磁性绝缘体衬底还将允许自旋电流的磁选通。第二，石墨烯中的自旋-轨道相互作用(SOI)是由于其他2D材料的接近而引起的。这些材料包括拓扑绝缘体、过渡金属二卤化物，以及具有巨大自旋-轨道耦合的新型2D材料，如BiTeI。感应SOI可以实现对自旋方向的电控制。SOI的存在将通过弱局域化和自旋霍尔测量来测试。还预言，如果石墨烯中存在适当的SO项，它可以获得拓扑性质并转变为量子自旋-霍尔相。此外，像BiTeI这样的新的2D材料本身也将对自旋电子学领域产生兴趣，这些材料也将为制造Van der Waals异质结构提供新的基础。最后，我们将通过使用金属超结构将真实空间纹理引入石墨烯。为此，铁磁和超导结构将被制造在石墨烯的顶部，由几层h-BN隔开。在这里，纳米磁铁的杂散场将被用来诱导出具有拓扑学意义的结构，如Skyrmions。石墨烯上的超导电极将抑制迈斯纳效应产生的磁场，使局部磁场的剪裁成为可能。这些局域磁场将用于自旋电子学和电子光学实验。为了实现我们的目标，我们将生产基于Van der Waals拾取技术的邻近结构，并将开发先进的制造方法，如点接触封装石墨烯，或由几层h-BN与石墨烯分开的金属超结构。这些实验将得到密度泛函和输运计算的支持。该提案中概述的方法和目标将使基于石墨烯的未来自旋电子学应用更加紧密。

After the discovery of graphene it was soon realized, that graphene is the perfect candidate for spintronics, due to its high mobility, low spin-orbit coupling and small or absent hyperfine fields. By now, spin relaxation lengths longer than 10 micrometers have been demonstrated. Although the results are still far from expectations, the achieved values already make graphene an ideal platform to transfer spin information. The key question at the present stage, how the manipulation of spin can be achieved with graphene devices. In this proposal we will investigate novel routes to add electric and magnetic control over the spin by introducing different spin textures in graphene. Spin textures are induced by developing various 2D proximity heterostructures: First, using magnetic insulators exchange interaction will be induced in graphene and in topological insulators. This will be confirmed by anomalous Hall measurements. Moreover, the magnetic insulator substrates will also allow magnetic gating of the spin-current. Second, spin-orbit interaction (SOI) will be induced in graphene by the proximity of other 2D materials. These materials include topological insulators, transition metal dichalcogenids, and novel 2D materials, with huge spin-orbit coupling, like BiTeI. The induced SOI can enable electrical control of the spin-direction. The presence of SOI will be tested by weak localization, and spin-Hall measurements. It is also predicted, that if the proper SO terms are present in graphene, it can acquire topological properties and turn into the quantum spin-Hall phase. Moreover, new 2D materials, like BiTeI will be interesting for the field of Spintronics by themselves and these materials will also give new building blocks for producing Van der Waals heterostructures. Finally, we will introduce real-space textures into graphene by using metallic superstructures. For this, ferromagnetic and superconducting structures will be fabricated on top of graphene, separated by few layers of h-BN. Here, the stray field of the nanomagnets will be used to induce topologically interesting structures, such as skyrmions. The superconducting electrodes on top of graphene will suppress the magnetic fields due to Meissner effect, and the tailoring of local magnetic fields will be possible. These local fields will be used for spintronics and electron-optical experiments. To achieve our goals we will produce proximity structures based on Van der Waals pick-up technique, and will develop advanced fabrication methods, like point-contacts to encapsulated graphene, or metallic superstructures separated from graphene by few layers of h-BN. The experiments will be supported by DFT and transport calculations. The methods and goals outlined in this proposal will bring graphene based future spintronics applications closer.