Abstract
Recently the presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI). Here, we present a density-functional-theory-based study on a family of TIs derived from the Bi14Rh3I9 parent structure via substitution of Ru, Pd, Os, Ir and Pt for Rh. Comparative analysis of the band-structures throughout the entire series is done by means of a unified minimalistic tight-binding model that evinces strong similarity between the quantum-spin-Hall (QSH) layer in Bi14Rh3I9 and graphene in terms of -molecular orbitals. Topologically non-trivial energy gaps are found for the Ir-, Rh-, Pt- and Pd-based systems, whereas the Os- and Ru-systems remain trivial. Furthermore, the energy position of the metal -band centre is identified as the parameter which governs the evolution of the topological character of the band structure through the whole family of TIs. The -band position is shown to correlate with the chemical bonding within the QSH layers, thus revealing how the chemical nature of the constituents affects the topological band character.
Highlights
The presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI)
This occurs in topological insulators that consist of stacked quantum spin Hall (QSH) layers[8], the rather ineptly named weak TIs (WTIs)
This paper addresses the questions whether Bi14Rh3I9 can foster a whole family of TIs upon substitutions of transition-metal atoms and what the role of chemical interaction is, in the formation of the topologically non-trivial state
Summary
The presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI). Does this feature strongly suppress back-scattering, it lays the foundation for novel types of information processing such as spintronics[5] by providing pure spin currents[6], or fault tolerant quantum computation by using the Majorana fermions at interfaces of topological states with superconductors[7] Manipulating such helical electrons becomes much easier if they self-organise into quasi one-dimensional channels. Being confined to a step-edge, these chiral edge-states are intrinsically one-dimensional and can in principle be manipulated by changing the step-edge geometry[12] Very recently these electron channels have been observed experimentally by scanning tunnelling microscopy[13] at the surface step-edges of Bi14Rh3I9, the first experimentally realised weak 3D TI14. This experimentally realised stack is immune to translational disorder along the stacking direction thanks to the high rigidity of the covalently-bonded QSH layer and the electrostatic interaction of the oppositely charged QSH and spacer layers[15]
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