Electronic band structure, magnetic and structural properties of magnetic atoms on Bi2Se3Cux

拓扑绝缘体是最近发现的材料，其主要特征是具有金属边缘或表面的绝缘体。由于其新颖的性质，拓扑绝缘体受到越来越多的关注。这些新材料的标志是无间隙拓扑表面态（TSS），它受到时间反转对称性的保护，免受非磁扰动的散射。拓扑状态对小表面扰动的鲁棒性已经被实验证明，特别是对于Bi2Se3，这是一个简单的三维拓扑绝缘体模型系统。一些理论工作已经预测了当磁性原子被吸附在Bi2Se3表面时，打破时间反转对称性并在TSS的狄拉克点打开能量缺口的可能性。然而，在实验方面，理论预测尚未得到满足。磁性原子在Bi2Se3上的吸附导致了TSS的n掺杂和在表面产生二维电子气体（2DEG）。在这个建议中，表面没有磁有序归因于表面存在2DEG。因此，建议使用cu掺杂的Bi2Se3晶体，避免了2DEG的产生，作为Bi2Se3的替代品来承载磁性原子。我们计划利用角分辨-光电光谱技术，实验研究不同磁性原子的吸附对cu掺杂Bi2Se3表面能带结构的影响，特别是对TSS的影响。在Dirac点出现一个缺口，这是磁原子/Bi2Se3Cux体系表面铁磁相发展的代名词。利用x射线磁圆二色技术研究表面的磁性能。最后，利用扫描隧道显微镜对该系统的局部结构和电子特性进行表征。

Topological Insulators are recently discovered materials characterized essentially by an insulating bulk with metallic edges or surfaces. Thanks to their novel properties, the topological insulators are subject of increasing interest. The hallmark of these new materials is the gapless topological surface state (TSS), which is protected by time-reversal symmetry against scattering from non-magnetic perturbations. The robustness of the topological state against small surface perturbation has been experimentally proven, particularly for Bi2Se3, which is a simple model system of three dimensional topological insulators. Several theoretical works have predicted the possibility to break time-reversal symmetry and open an energy gap at the Dirac point of the TSS, when magnetic atoms are adsorbed on the surface of Bi2Se3. However, on the experimental side, the theoretical predictions have not been satisfied yet. The adsorption of magnetic atoms on Bi2Se3 has rather resulted in an n-doping of the TSS and the creation of a two-dimensional electron gas (2DEG) at the surface.In this proposal, the absence of magnetic ordering at the surface is attributed to the presence of the 2DEG at the surface. Therefore, it is proposed to use the Cu-doped Bi2Se3 crystal, where the creation of the 2DEG is avoided, as an alternative to Bi2Se3 to host the magnetic atoms. It is planned to experimentally investigate the effect of adsorption of different magnetic atoms on the surface band structure of Cu-doped Bi2Se3, and in particular, on the TSS, using angle-resolved-photoemission-spectroscopy. A gap opening at the Dirac point, synonym of a development of a ferromagnetic phase at the surface of the magnetic-atom/Bi2Se3Cux system, is expected. The magnetic properties of the surface will be investigated using X-ray Magnetic Circular Dichroism technique. Finally, the local structural and electronic characteristics of the above system will be characterized using scanning tunneling microscopy.