Sn-Al Lieb格子二维薄膜材料的制备和拓扑物性研究

Lieb格子在理论上具有Dirac锥和平带交叠的特殊能带结构，有望实若干拓扑非平庸拓扑物相，并且显示拓扑相的可调性。然而具有本征平带和拓扑性质的Lieb格子二维材料，目前仍处于缺失的状态。本项目拟利用分子束外延生长的方法在若干非金属衬底上制备的Sn-Al两种元素组成的Lieb格子薄膜，并且利用扫描隧道显微镜、角分辨光电子能谱等表面技术建立其原子结构与电子结构之间的关联。在获得高质量的Lieb格子二维材料的基础上，进一步通过调控衬底与薄膜的相互作用、重元素和磁性掺杂、碱金属吸附等手段从实验上验证Lieb格子中拓扑相的可调性，以及建立电子跃迁矩阵、晶格对称性破缺、轨道杂化、电荷转移、SOC等与其本征电子结构和拓扑物性的关系。从而为掌握和了解Lieb格子中的拓扑非平庸电子结构的物理本质奠定实验基础，并为在Lieb格子二维体系中实现奇异的拓扑量子态提供可行的技术路线。

Lieb lattice is a two-dimensional (2D) frustrated lattice in which the atoms are arranged in an edge-centered square lattice with three atoms per unit cell. Lieb lattice hosts a unique electronic structure in the low-energy regime, in which a flat band is sandwiched by two linear-dispersive bands (known as Dirac cones) at the M point of the Brillouin zone, if the electrons only engage in the nearest-neighbor hopping in the tight binding calculations. The Dirac cones give rise to massless carriers, while the flat band could enable realization of the fractional quantum Hall effect, superconductivity, and various topological nontrivial phases. Its intriguing electronic structure associated with some exotic quantum states is of importance for both fundamental physics and practical applications, arousing intensive studies of the Lieb lattice in the past decade. However, 2D solid materials in Lieb lattice that show electronic flat band and topological non-trivial properties are still missing.. .In this project, we are aiming at synthesizing Sn-Al Lieb lattice on non-metallic substrates by molecular-beam epitaxy and exploiting their intrinsic topological properties by STM and ARPES. Furthermore, on the basis of obtaining high-quality thin film, the tunability of the topological phases of Sn-Al Lieb lattice by the interaction between the segmented substrate and the film, doping effect of heavy and ferromagnetic elements, the adsorption of alkali metals will be checked experimentally. Then the relationship between electronic hopping matrix, lattice symmetry breaking, orbital hybridization, charge transfer, SOC and the intrinsic electronic structure as well as topological properties will be established. The realization of Lieb lattice 2D film with intrinsic topological properties, and the insights on their origins will greatly promote our understanding of their symmetry-related electronic and topological properties for the exploration of novel physical properties and applications.