Two-Dimensional Inversion Asymmetric Topological Insulators in Functionalized III-Bi Bilayers (original) (raw)
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Bi1Te1 is a dual topological insulator
Nature communications, 2017
New three-dimensional (3D) topological phases can emerge in superlattices containing constituents of known two-dimensional topologies. Here we demonstrate that stoichiometric Bi1Te1, which is a natural superlattice of alternating two Bi2Te3 quintuple layers and one Bi bilayer, is a dual 3D topological insulator where a weak topological insulator phase and topological crystalline insulator phase appear simultaneously. By density functional theory, we find indices (0;001) and a non-zero mirror Chern number. We have synthesized Bi1Te1 by molecular beam epitaxy and found evidence for its topological crystalline and weak topological character by spin- and angle-resolved photoemission spectroscopy. The dual topology opens the possibility to gap the differently protected metallic surface states on different surfaces independently by breaking the respective symmetries, for example, by magnetic field on one surface and by strain on another surface.
The search for strongly inversion asymmetric topological insulators is an active research field because these materials possess distinct properties compared with the inversion symmetric ones. In particular, it is desirable to realize a large Rashba spin-splitting (RSS) in such materials, which combined with the topological surface states (TSS) could lead to useful spintronics applications. In this report, based on first principles calculations, we predict that the heterostructure of BiTeI/Bi 2 Te 3 is a strong topological insulator with a giant RSS. The coexistence of TSS and RSS in the current system is native and stable. More importantly, we find that both the Z 2 invariants and the Rashba energy can be controlled by engineering the layer geometries of the heterostructure, and the Rashba energy can be made even larger than that of bulk BiTeI. Our work opens a new route for designing topological spintronics devices based on inversion asymmetric heterostructures. OPEN SUBJECT AREAS: TOPOLOGICAL INSULATORS ELECTRONIC PROPERTIES AND MATERIALS SPINTRONICS SEMICONDUCTORS
Coexisting surface states in the weak and crystalline topological insulator Bi_2TeI
arXiv: Mesoscale and Nanoscale Physics, 2017
The established diversity of electronic topology classes lends the opportunity to pair them into dual topological complexes. Bulk-surface correspondence then ensures the coexistence of a combination of boundary states that cannot be realized but only at the various surfaces of such a dual topological material. We show that the layered compound Bi_2TeI realizes a dual topological insulator. It exhibits band inversions at two time reversal symmetry points of the bulk band which classify it as a weak topological insulator with metallic states on its (010) 'side' surfaces. Additional mirror symmetry of the crystal structure concurrently classifies it as a topological crystalline insulator. Bi2TeI is therefore predicted to host a pair of Dirac cones protected by time reversal symmetry on its 'side' surfaces and three pairs of Dirac cones protected by mirror symmetry on its 'top' and 'bottom' (001) surfaces. We spectroscopically map the top cleaved surface ...
Journal of Physics: Condensed Matter
The goal of the present review is to cross-compare theoretical predictions with selected experimental results of spin-and angle-resolved photoelectron spectroscopy on bismuth thin films exhibiting topological properties and a strong Rashba effect. Despite the bulk Bi crystal is topologically trivial, a single free-standing Bi(1 1 1) bilayer has been predicted by calculations to be a topological insulator. This triggered a large series of studies of ultrathin Bi(1 1 1) films grown on various substrates. Using selected examples we review theoretical predictions of atomic and electronic structure of Bi thin films exhibiting topological properties due to interaction with a substrate. We survey as well experimental signatures of topological surface states, as obtained namely by angle-resolved photoelectron spectroscopy.
Ab initio study of 2DEG at the surface of topological insulator Bi2Te3
JETP Letters, 2012
Over the past few years three dimensional topolog ical insulators (TIs) have attracted extensive interest due to their spin momentum locked metallic surface states (SSs) . These kinds of materials are narrow gap semiconductors characterized by an inverted energy gap caused by spin-orbit coupling (SOC). Unlike SSs in ordinary materials, these SSs show lin ear dispersion, forming a Dirac cone with a crossing (Dirac) point at/near the Fermi level (E F ) . This topological SS carries only a single electron per momentum with a spin that changes its direction con sistently with a change of momentum. The topological origin of the SS protects the Dirac cone from surface perturbations [1]. The unique electronic properties of the surface of the topological insulators make these materials important for many interesting applications, particularly in spintronics and quantum computing.
Nature Communications, 2013
Topological insulators represent a new class of quantum phase defined by invariant symmetries and spin-orbit coupling that guarantees metallic Dirac excitations at its surface. The discoveries of these states have sparked the hope of realizing non-trivial excitations and novel effects such as a magnetoelectric effect and topological Majorana excitations. Here we develop a theoretical formalism to show that a three-dimensional topological insulator can be designed artificially via stacking bilayers of two-dimensional Fermi gases with opposite Rashba-type spin-orbit coupling on adjacent layers, and with interlayer quantum tunneling. We demonstrate that in the stack of bilayers grown along a (001)-direction, a non-trivial topological phase transition occurs above a critical number of Rashba bilayers. In the topological phase, we find the formation of a single spin-polarized Dirac cone at the G-point. This approach offers an accessible way to design artificial topological insulators in a set up that takes full advantage of the atomic layer deposition approach. This design principle is tunable and also allows us to bypass limitations imposed by bulk crystal geometry.
Interfacing 2D and 3D Topological Insulators: Bi(111) Bilayer on Bi_{2}Te_{3}
Physical Review Letters, 2011
We report the formation of a bilayer Bi(111) ultrathin film, which is theoretically predicted to be in a two-dimensional quantum spin Hall state, on a Bi 2 Te 3 substrate. From angle-resolved photoemission spectroscopy measurements and ab initio calculations, the electronic structure of the system can be understood as an overlap of the band dispersions of bilayer Bi and Bi 2 Te 3. Our results show that the Dirac cone is actually robust against nonmagnetic perturbations and imply a unique situation where the topologically protected one-and two-dimensional edge states are coexisting at the surface.
Strong and Weak Three‐Dimensional Topological Insulators Probed by Surface Science Methods
physica status solidi (b)
We review the contributions of surface science methods to discover and improve 3D topological insulator materials, while illustrating with examples from our own work. In particular, we demonstrate that spin-polarized angularresolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy towards the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, we introduce procedures to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators.
Large insulating gap in topological insulators induced by negative spin-orbit splitting
Physical Review B, 2012
In a cubic topological insulator (TI), there is a band inversion whereby the s-like 6c conduction band is below the p-like 7v + 8v valence bands by the "inversion energy" i < 0. In TIs based on the zinc-blende structure such as HgTe, the Fermi energy intersects the degenerate 8v state so the insulating gap E g between occupied and unoccupied bands vanishes. To achieve an insulating gap E g > 0 critical for TI applications, one often needs to resort to structural manipulations such as structural symmetry lowering (e.g., Bi 2 Se 3 ), strain, or quantum confinement. However, these methods have thus far opened an insulating gap of only <0.1 eV. Here we point out that there is an electronic rather than structural way to affect an insulating gap in a TI: if one can invert the spin-orbit levels and place 8v below 7v ("negative spin-orbit splitting"), one can realize band inversion ( i < 0) with a large insulating gap (E g up to 0.5 eV). We outline design principles to create negative spin-orbit splitting: hybridization of d orbitals into p-like states. This general principle is illustrated in the "filled tetrahedral structures" (FTS) demonstrating via GW and density functional theory (DFT) calculations E g > 0 with i < 0, albeit in a metastable form of FTS.