Interfacing 2D and 3D Topological Insulators: Bi(111) Bilayer on Bi_{2}Te_{3} (original) (raw)
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Experimental Realization of a Three-Dimensional Topological Insulator, Bi2Te3
Science, 2009
We report the first observation of a topological surface state on the (111) surface of the ternary chalcogenide TlBiSe 2 by angle-resolved photoemission spectroscopy. By tuning the synchrotron radiation energy we reveal that it features an almost ideal Dirac cone with the Dirac point well isolated from bulk continuum states. This suggests that TlBiSe 2 is a promising material for realizing quantum topological transport.
Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface
Nature Physics, 2009
Topological insulators are new states of quantum matter in which surface states residing in the bulk insulating gap of such systems are protected by time-reversal symmetry. The study of such states was originally inspired by the robustness to scattering of conducting edge states in quantum Hall systems. Recently, such analogies have resulted in the discovery of topologically protected states in two-dimensional and three-dimensional band insulators with large spin-orbit coupling. So far, the only known three-dimensional topological insulator is Bi x Sb 1−x , which is an alloy with complex surface states. Here, we present the results of first-principles electronic structure calculations of the layered, stoichiometric crystals Sb 2 Te 3 , Sb 2 Se 3 , Bi 2 Te 3 and Bi 2 Se 3 . Our calculations predict that Sb 2 Te 3 , Bi 2 Te 3 and Bi 2 Se 3 are topological insulators, whereas Sb 2 Se 3 is not. These topological insulators have robust and simple surface states consisting of a single Dirac cone at the point. In addition, we predict that Bi 2 Se 3 has a topologically non-trivial energy gap of 0.3 eV, which is larger than the energy scale of room temperature. We further present a simple and unified continuum model that captures the salient topological features of this class of materials.
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.
2009
Three dimensional (3D) topological insulators are quantum materials with a spin-orbit induced bulk insulating gap that exhibit quantum-Hall-like phenomena in the absence of applied magnetic fields. They feature surface states that are topologically protected against scattering by time reversal symmetry. The proposed applications of topological insulators in device geometries rely on the ability to tune the chemical potential on their surfaces in the vicinity of the Dirac node.
Physical Review Letters, 2012
Helical spin textures with marked spin polarizations of topological surface states have been unveiled for the first time by state-of-the-art spin-and angle-resolved photoemission spectroscopy for two promising topological insulators, Bi 2 Te 2 Se and Bi 2 Se 2 Te. Their highly spin-polarized natures are found to be persistent across the Dirac point in both compounds. This novel finding paves a pathway to extending the utilization of topological surface states of these compounds for future spintronic applications.
Robustness of Topologically Protected Surface States in Layering of Bi_{2}Te_{3} Thin Films
Physical Review Letters, 2010
Bulk Bi2Te3 is known to be a topological insulator. We investigate surface states of Bi2Te3(111) thin films using density-functional theory including spin-orbit coupling. We construct a method to unambiguously identify surface states of thin film topological insulators. Applying this method for one to six quintuple layers of Bi2Te3, we find that the topological nature of the surface states remains robust with the film thickness and that the films of three or more quintuple layers have topologically non-trivial or protected surface states, in agreement with recent experiments.
Physical Review Letters, 2009
We show that the strongly spin-orbit coupled materials Bi 2 Te 3 and Sb 2 Te 3 and their derivatives belong to the Z 2 topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi 2 Te 3 is a large spin-orbit-induced indirect bulk band gap ( $ 150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb 2 Te 3 exhibits similar Z 2 topological properties. We demonstrate that the dynamics of spin-Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for topological device applications.
The emergence of topologically protected surface states in epitaxial Bi(111) thin films
arXiv (Cornell University), 2014
Quantum transport measurements including the Altshuler-Aronov-Spivak (AAS) and Aharonov-Bohm (AB) effects, universal conductance fluctuations (UCF), and weak anti-localization (WAL) have been carried out on epitaxial Bi thin films (10 − 70 bilayers) on Si(111). The results show that while the film interior is insulating all six surfaces of the Bi thin films are robustly metallic. We propose that these properties are the manifestation of a novel phenomenon, namely, a topologically trivial bulk system can become topologically non-trivial when it is made into a thin film. We stress that what's observed here is entirely different from the predicted 2D topological insulating state in a single bilayer Bi where only the four side surfaces should possess topologically protected gapless states.
New Journal of Physics, 2015
Proximity-induced magnetic effects on the surface Dirac spectra of topological insulators are investigated by scanning tunneling spectroscopic (STS) studies of bilayer structures consisting of undoped Bi2Se3 thin films on top of Cr-doped Bi2Se3 layers. For thickness of the top Bi2Se3 layer equal to or smaller than 3 quintuple layers (QL), a spatially inhomogeneous surface spectral gap opens up below a characteristic temperature Tc 2D , which is much higher than the bulk Curie temperature Tc 3D determined from the anomalous Hall resistance. The mean value and spatial homogeneity of the gap generally increase with increasing c-axis magnetic field (H) and increasing Cr doping level (x), suggesting that the physical origin of this surface gap is associated with proximity-induced c-axis ferromagnetism. On the other hand, the temperature (T) dependence of is non-monotonic, showing initial increase below Tc 2D , which is followed by a "dip" and then rises again, reaching maximum at T << Tc 3D. These phenomena may be attributed to proximity magnetism induced by two types of contributions with different temperature dependences: a three-dimensional contribution from the bulk magnetism that dominates at low T, and a two-dimensional contribution associated with the RKKY interactions mediated by surface Dirac fermions, which dominates at Tc 3D << T < Tc 2D. In addition to the observed proximity magnetism, spatially localized sharp resonant spectra are found along the boundaries of gapped and gapless regions. These spectral resonances are long-lived at H = 0, with their occurrences being most prominent near Tc 2D and becoming suppressed under strong c-axis magnetic fields. We attribute these phenomena to magnetic impurity-induced topological defects in the spin texture of surface Dirac fermions, with the magnetic impurities being isolated Cr impurities distributed near the interface of the bilayer system. The long-term stability of these topologically protected two-level states may find potential applications to quantum information technology.