Magnetic and electronic properties of graphene/MOFene superlattices

在第一个资助期，我们建立了由石墨烯和结晶二维聚合物垂直堆叠制成的异质结构（HS）的制造。我们在理论和实验的基础上对其结构和电子结构进行了全面的表征和了解。我们在硅中研究了典型衬底存在和不存在的HS波纹以及波纹对能带结构的影响。在2DPI/石墨烯HS中，我们能够显示出强烈的层内电荷转移，光谱特征的增强，以及由于层间相互作用而导致石墨烯中带隙打开的第一个迹象。在建立了从理论上和实验上获得这种HS纳米级电子特性的总体策略之后，我们将在第二个资助期内关注二维金属有机框架（所谓的MOFenes）和各种石墨烯系统（石墨烯和门控伯纳堆叠双层石墨烯，gBLG）之间更微妙的磁相互作用。这些框架包含金属中心作为由有机配体连接的节点元素，金属中心携带电荷和/或自旋中心。因此，具有特征晶格的MOFenes将在任何界面二维材料（如石墨烯或gBLG）上施加相同结构的电荷/磁超晶格。在这样的HS中，我们将能够研究晶格拓扑结构和不同金属中心对HS磁性的影响。我们将从实验和理论两方面探讨蜂窝状、菱形晶格和菱形晶格拓扑中MOFenes的磁和电子层内耦合。这允许调整层内与层间的磁耦合，从而产生宏观磁性。最有趣的是，我们将能够研究MOFene的磁性和层内自旋轨道耦合对我们最近在可调谐van-Hove奇点附近的gBLG中发现的复杂相关态的影响。这些研究的中心目标是了解不同拓扑结构的超晶格效应。虽然对所有晶格来说，磁中心的铁磁和反铁磁有序都是可能的，但在kagome晶格中，自旋受挫要么会产生铁磁有序，要么会产生自旋液体。由于相互作用可以通过选择磁中心和配体来调节，这种有趣的二维自旋液体系统将变得可行。本研究采用了丰富的实验和理论方法，包括先进的材料转移技术、量子输运、扫描近场显微镜、纳米级扫描光谱、正交紧密结合哈密顿、密度泛函理论（DFT）、基于DFT的紧密结合和准粒子方法。

In the first funding period we established the manufacturing of heterostructures (HS) made from vertical stacks of graphene and a crystalline two-dimensional polymer. We thoroughly characterized and understood its structure and electronic structure on ground of theory and experiment. We investigated in silico the corrugation of the HS presence and absence of typical substrates and the impact of the corrugation on the band structure. r In a 2DPI/graphene HS we were able to show strong intralayer charge transfer, enhancement of spectral features as well as first indications of a bandgap opening in graphene due to the interlayer interaction. Having established the general strategy to access the nanoscale electronic properties of such HS both theoretically and experimentally, we will focus on the more subtle magnetic interactions between 2D metal-organic frameworks, so-called MOFenes, and various graphene systems (graphene and gated Bernal-stacked bilayer graphene, gBLG) during the second funding period. These frameworks contain metal centers as nodal elements connected by organic ligands, and the metal centers carry charge and/or spin centers. MOFenes with a characteristic lattice thus will impose a charge/magnetic superlattice of the same structure on any interfaced 2D material, such as graphene or gBLG. In such HSs we will be able to investigate effects of lattice topology and different metal centers on the resulting magnetism of the HS. We will explore magnetic and electronic intralayer coupling in the MOFenes of honeycomb, kagome and rhombic lattice topology both experimentally and theoretically. This allows to tune the intra versus interlayer magnetic coupling and thus the resulting macroscopic magnetic properties. Most intriguingly, we will be able to investigate the impact of magnetism and intralayer spin-orbit coupling of the MOFene on the intricate correlated states we recently identified in gBLG near its tunable van-Hove singularity. A central goal of these investigations is the understanding of superlattice effects of different topology. While for all lattices ferromagnetic and antiferromagnetic ordering of the magnetic centers is possible, in the kagome lattice spin frustration should either should give ferromagnetic ordering or a spin liquid. As interactions can be tuned by the choice of magnetic centers and ligands, such intriguing 2D spin-liquid systems will become feasible. This proposal employs a rich range of experimental and theoretical methods, including advanced material transfer techniques, quantum transport, scanning near-field microscopy, nanoscale scanning spectroscopy, orthogonal tight-binding hamiltonians, density-functional theory (DFT), DFT based tight-binding, and quasiparticle methods.