拓扑半金属Sb薄膜的分子束外延生长、能带结构调控和原位同步辐射ARPES研究

拓扑绝缘体是一类自旋轨道耦合作用引起的新量子物质态，已成为当前凝聚态物理研究的热点之一。半金属Sb具有与拓扑绝缘体相同的自旋极化金属表面态，是高温自旋流源的理想候选人，但因制备方法的局限一直研究较少。本项目利用分子束外延技术，直接在Si(111)表面，精确可控地生长1 BL至100 BL层厚的大面积原子级平整Sb薄膜，并对其实现Cr、Cu、 O2等磁性、非磁性原子的可控掺杂和吸附。利用原位同步辐射角分辨光电子能谱，通过改变光子能量在整个布里渊区分离体能带和表面能带，通过改变光子极化获得能带自旋信息，系统研究量子尺寸效应和掺杂效应对Sb薄膜能带结构的调控。从三维到二维、从有磁到无磁，实现Sb薄膜从拓扑半金属到拓扑绝缘体、从拓扑非平庸态到拓扑平庸态的转变，探索磁有序、超导相与Sb薄膜拓扑表面态的相互作用规律，明确氧化对Sb薄膜拓扑表面态的影响，为Sb薄膜拓扑表面态独特性质的研究和应用奠定基础。

Topological insulator with strong spin-orbit coupling, a new state of quantum matter, is currently one of the hot topics in condensed matter physics. Sb, a bulk semimetal, has a gapless spin-polarized surface state like topological insulators, which will be a promising candidate for high-temperature spin current sources. However, due to the limited fabrication methods, Sb has attracted less attention. In this work, atomically flat Sb thin films with macroscopically large area are directly prepared on Si(111) from 1 BL to 100 BL by molecular beam epitaxy and studied by in-situ scanning tunneling microscopy and synchrotron-radiation angle-resolved photoemission spectroscopy. Using variable photon energies and polarizations, the topological surface states of Sb films are successfully isolated from bulk states over the entire Brillouin zone and their different spin structures are identified. Due to the large quantum confinemet length, quantum size effect are quite sensitive in Sb films. With decreasing thickness of confinement, the surface states and bulk states of Sb films are effectively tuned, which causes the transitons from three-dimensional topological semimetal to three-dimensional topological insulator and from topologically nontrivial state to topologically trivial state. Besides, Cr and Cu atoms are doped in Sb thin films, respectively. By breaking time-reversal symmetry with proximity to a magnetic material and by breaking gauge symmetry due to proximity to a superconductor, an energy gap is expected to be induced into the topological surface state. Finally, the influence of O2 adsorption on topological surface states will be explored. This work will be a basis of unique property investigations and ultimate applications of topological surface states in Sb films.