Abstract:
Over the past decade, topological phases in condensed matter systems have attracted worldwide research interest. [1,2] Among these novel phases, quantum spin Hall (QSH) insulators, or so-called two-dimensional (2D) topological insulators (TIs), possess exotic edge-state electronic structures.[3] Three-dimensional (3D) TIs feature a bulk energy gap and time-reversal symmetry-protected gapless surface states derived from spin−orbit coupling (SOC), which are distinct from conventional band insulators. While many materials have been shown to be 3D TIs, much less research has been done on 2D TIs. HgTe-based quantum wells (QWs) were first experimentally demonstrated to be QSH insulators,[4] but HgTe QWs have serious limitations, such as toxicity and processing difficulties. Alternatively, research on 2D TI with larger gaps becomes intensive. For example, many efforts have been made to explore candidate compounds for large-gap 2D TIs, such as Ge, [5]Sn, [6]Sb, [7], and Bi[8].
So far, most of these 2D TIs have been prepared by growth or the so called “bottom-up method” or by exfoliation]. Due to the island-like growth mode, the sample surface is often too rough to achieve 2D TI. In practical applications, the exfoliation method is difficult to control the size and smoothness of the sample. We have developed a deliberate atomic hydrogen etching (AHE) technique, the so called “top-down approach”, for the preparation of 2D TIs from 3D TIs. With AHE, large-area, smooth-surfaced 2D TIs including bismuth and antimonene can be achieved. [9, 10] We investigated the formation process and surface structure of bismuth (Bi-bilayer) and antimonene (Sb-bilayer) using STM/STS. The band structure and topological properties of these 2D TIs were explored by angle resolved photoemission spectroscopy (ARPES), and the results were compared with DFT calculations. We found a large Rashba Splitting effect in the case of bismuthene/Bi2Se3. For antimonene /Sb2Te3, a topologically protected state was formed at the interface due to strong topological proximity effect. Our study shows that the topology, Dirac points, and electron spin orientations of surface states of 2D TIs can be controlled by a heterostructure composed of 2D TIs/3D TIs. This work has made breakthroughs in the preparation of novel 2D materials, and the study of energy band and spin manipulation.
Keywords - List key keywords here. No more than 5. quantum spin Hall, 2D and 3D topological insulators, atomic hydrogen etching, bismuthene, antimonene, Rashba Splitting, topological proximity effect
References:
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