Electronic Structure of the Dark Surface of the Weak Topological Insulator Bi14Rh3I9

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• 作者：Christian Pauly ; Bertold Rasche ; Klaus Koepernik ; Manuel Richter ; Sergey Borisenko ; Marcus Liebmann ; Michael Ruck ; Jeroen van den Brink ; Markus Morgenstern
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：April 26, 2016
• 年：2016
• 卷：10
• 期：4
• 页码：3995-4003
• 全文大小：557K
• 年卷期：0
• ISSN：1936-086X

文摘

Compound Bi₁₄Rh₃I₉ consists of ionic stacks of intermetallic [(Bi₄Rh)₃I]²⁺ and insulating [Bi₂I₈]^2– layers and has been identified to be a weak topological insulator. Scanning tunneling microscopy revealed the robust edge states at all step edges of the cationic layer as a topological fingerprint. However, these edge states are found 0.25 eV below the Fermi level, which is an obstacle for transport experiments. Here, we address this obstacle by comparing results of density functional slab calculations with scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. We show that the n-type doping of the intermetallic layer is intrinsically caused by the polar surface and is well-screened toward the bulk. In contrast, the anionic “spacer” layer shows a gap at the Fermi level, both on the surface and in the bulk; that is, it is not surface-doped due to iodine desorption. The well-screened surface dipole implies that a buried edge state, probably already below a single spacer layer, is located at the Fermi level. Consequently, a multilayer step covered by a spacer layer could provide access to the transport properties of the topological edge states. In addition, we find a lateral electronic modulation of the topologically nontrivial surface layer, which is traced back to the coupling with the underlying zigzag chain structure of the spacer layer.