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Abstract:
Compound Bi14Rh3I9 consists of ionic stacks of intermetallic
[(Bi4Rh)(3)I](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.
