Bismuth‐based candidates for topological insulators: Chemistry beyond Bi₂Te₃

Abstract

IntroductionThe booming field of topological insulators has established an elaborate, consistent theory and is now tackling further challenges such as the search for topologically protected systems with strong electron interactions and systems capable of demonstrating the Majoranafermion phenomenon. A fascinating goal looming a little ways down the road is fault-tolerant quantum computing [1].On this way we are challenged by many engineering and chemical problems. For instance, bismuth-chalcogenide TIs have to be tuned by well-controlled doping, and investigations of predicted 3D TIs with nearly cubic structures are hampered by exfoliation failures. Whereas many studies are aiming at nanostructurization of Bi 2 Q 3 , Q = Se, Te (in organic solutions [2], on mica substrates [3]) and tuning it for future applications (synthesis of ultrathin films [4] and heterostructures where quintuple layers of Bi 2 Q 3 are interlaced with insulating slabs [5]), the search for new candidate compounds is also underway.

Vibrational properties of epitaxial Bi4Te3 films as studied by Raman spectroscopy

“…The unit cell contains three Bi 2 slabs and three QL slabs, one third of which is arranged in the following order: -(Te 1 -Bi 1 -Te 2 -Bi 1 -Te 1 )-(Bi 2 -Bi 2 )-. Atoms inside both the Bi 2 slabs and the QL slabs are covalently connected 15,16 whereas the interactions between the Bi 2 and the QL slabs are of a weak covalent nature. 10 Assessed by the bond-length-bond-strength concept, the structure of Bi 4 Te 3 has the weakest bonding at the slab boundaries.…”

“…1(b)). Based on the bonding abilities of Bi governed by its 6p orbitals, 15 each Bi atom is bonded to three intra-bilayer partners at 3.07 Å and to three inter-bilayer partners at 3.53 Å. As a result, each Bi atom has three nearest-neighbor bonds, forming the stable Bi 2 slabs with strong intra-bilayer covalent bonds in bismuth films.…”

“…As a result, each Bi atom has three nearest-neighbor bonds, forming the stable Bi 2 slabs with strong intra-bilayer covalent bonds in bismuth films. 15,21 Bi 4 Te 3 films can be considered to have a structure where the Bi 2 slab is inserted into the Bi 2 Te 3 film structure periodically. 10,22 Taking into account the properties of the Bi 2 atoms, the Bi 2 slabs in Bi 4 Te 3 can be further viewed as ultrathin Bi films with a thickness of only one bilayer.…”

Pressure effect and superconductivity in theβ−Bi4I4topological insulator

“…The crystal structure of β-Bi4I4 is composed of narrow one-dimensional metallic bismuth stripes that extend along the b crystallographic axis [5,6]. These 1D building blocks are held together by weak non-covalent bonds, forming 2D layers parallel to each other that in turn pile up making a 3D bulk single crystal [5,7]. Both first-principles electronic structure calculations and angle-resolved photoemission spectroscopy (ARPES) studies demonstrate that β-Bi4I4 is at the boundary of a strongweak topological insulator phases and a trivial insulator one [4].…”

Topological Insulators – From Materials Design to Reality

“…Five experimental papers [1][2][3][4][5] We present ten Letters that cover various aspects, ranging from ARPES, transport measurement and devices, thin film growth to first-principles simulations and fundamental theory. Letters on ARPES [11][12][13][14] [18] shows the dependence of edge state dispersion on edge geometry of graphene.…”