Helical edge and surface states in HgTe quantum wells and bulk insulators
191
Citation
22
Reference
10
Related Paper
Citation Trend
Abstract:
The quantum spin Hall (QSH) effect is the property of a new state of matter which preserves time-reversal, has an energy gap in the bulk, but has topologically robust gapless states at the edge. Recently, it has been shown that HgTe quantum wells realize this novel effect. In this work, we start from realistic tight-binding models and demonstrate the existence of the helical edge states in HgTe quantum wells and calculate their physical properties. We also show that 3d HgTe is a topological insulator under uniaxial strain, and show that the surface states are described by single-component massless relativistic Dirac fermions in 2+1 dimensions. Experimental predictions are made based on the quantitative results obtained from realistic calculations.Keywords:
Topological insulator
Gapless playback
Massless particle
Surface States
A workable model for describing dislocation lines introduced into a three-dimensional topological insulator is proposed. We show how fragile surface Dirac cones of a weak topological insulator evolve into protected gapless helical modes confined to the vicinity of a dislocation line. It is demonstrated that surface Dirac cones of a topological insulator (either strong or weak) acquire a finite-size energy gap when the surface is deformed into a cylinder penetrating the otherwise surfaceless system. We show that, when a dislocation with a nontrivial Burgers vector is introduced, the finite-size energy gap plays the role of stabilizing the one-dimensional gapless states.
Gapless playback
Topological insulator
Burgers vector
Surface States
Cite
Citations (57)
Topological insulator
Gapless playback
Surface States
Cite
Citations (5)
Bi2Te3 is a topological insulator with time reversal symmetry possessing a single Dirac cone at a given surface. The surface states of topological insulators play a critical role in exotic physical phenomena and their applications. We investigate the surface states of thin films of Bi2Te3(111) using density‐functional theory including spin‐orbit coupling. Considering one to six quintuple layers (QLs) of Bi2Te3 films, we identify the surface states from calculated band structures using the decay length of the surface states and electron density plots. We show that the films of 1 and 2 QLs are too thin to hold the surface states protected topologically, and that for thicker films bands identified as surface states at Γ̄ lose their surface‐state features away from Γ̄. This method can be applied to other topological insulators.
Topological insulator
Surface States
Density of states
Cite
Citations (0)
From a viewpoint of transport properties, topological insulators are the materials that are insulating in the bulk but are metallic at their edge. After briefly introducing the basic phenomena such as Dirac fermions and quantum spin Hall effect for topological insulators, we describe the details of the quantum oscillations originating from the surface state of a three-dimensional topological insulator Bi1-xSbx, which was observed for the first time by our group. Intriguingly, this material was found to exhibit a novel angular-dependent magnetoresistance oscillation phenomenon, whose origin is still unknown but probably reflects a new physics in the surface transport properties of the topological insulator.
Topological insulator
Surface States
Cite
Citations (0)
Quantitative analysis of the weak antilocalization (WAL) effect of topological surface states in topological insulators is of tremendous importance. The major obstacle to achieve accurate results is how to eliminate the contribution of the anisotropic magnetoconductance of bulk states when the Fermi level lies in bulk bands. Here, we demonstrate that we can analyze quantitatively and accurately the WAL effect of topological surface states in topological insulator, BiSbTeSe2 (BSTS), by measuring the anisotropic magnetoconductance. The anomalous conductance peaks induced by the WAL effect of topological surface states of BSTS together with the anisotropic magnetoconductance of bulk states have been observed. By subtracting the anisotropic magnetoconductance of bulk states, we are able to analyze the WAL effect of topological surface states using the Hikami–Larkin–Nagaoka expression. Our findings offer an alternative strategy for the quantitative exploration of the WAL effect of topological surface states in topological insulators.
Topological insulator
Surface States
Cite
Citations (31)
The quantum spin Hall (QSH) effect is the property of a new state of matter which preserves time-reversal, has an energy gap in the bulk, but has topologically robust gapless states at the edge. Recently, it has been shown that HgTe quantum wells realize this novel effect. In this work, we start from realistic tight-binding models and demonstrate the existence of the helical edge states in HgTe quantum wells and calculate their physical properties. We also show that 3d HgTe is a topological insulator under uniaxial strain, and show that the surface states are described by single-component massless relativistic Dirac fermions in 2+1 dimensions. Experimental predictions are made based on the quantitative results obtained from realistic calculations.
Topological insulator
Gapless playback
Massless particle
Surface States
Cite
Citations (191)
The Dirac cone on a surface of a topological insulator shows linear dispersion analogous to optics and its velocity depends on materials. We consider a junction of two topological insulators with different velocities, and calculate the reflectance and transmittance. We find that they reflect the backscattering-free nature of the helical surface states. When the two velocities have opposite signs, both transmission and reflection are prohibited for normal incidence, when a mirror symmetry normal to the junction is preserved. In this case we show that there necessarily exist gapless states at the interface between the two topological insulators. Their existence is protected by mirror symmetry, and they have characteristic dispersions depending on the symmetry of the system.
Topological insulator
Gapless playback
Surface States
Mirror symmetry
Reflection
Cite
Citations (111)
The ternary topological insulator Bi2Te2Se is exceptional as it has a larger bulk resistivity than previously studied topological insulators. Here we explored the possibility of modifying the topological surface states and achieving the insulating massive Dirac fermion state in Bi2Te2Se on the basis of density functional calculations. Substitution of O for the outmost-layer Te leads to tunable surface states with an ideal Dirac cone. The co-substitution of Cr and O, as well as that of Mn and F, for the surface Bi and Te places the Dirac point inside the bulk band gap and opens a band gap at the Dirac point, hence creating the insulating massive Dirac fermion state. The co-substitution of magnetic and non-magnetic elements is a promising way of tuning the properties of topological insulators.
Topological insulator
Surface States
Cite
Citations (6)
Topological insulators in the ${\text{Bi}}_{2}{\text{Se}}_{3}$ family have an energy gap in the bulk and a gapless surface state consisting of a single Dirac cone. Low-frequency optical absorption due to the surface state is universally determined by the fine-structure constant. When the thickness of these three-dimensional topological insulators is reduced, they become quasi-two-dimensional insulators with enhanced absorbance. The two-dimensional insulators can be topologically trivial or nontrivial depending on the thickness, and we predict that the optical absorption is larger for topological nontrivial case compared with the trivial case. Since the three-dimensional topological insulator surface state is intrinsically gapless, we propose its potential application in wide bandwidth, high-performance photodetection covering a broad spectrum ranging from terahertz to infrared. The performance of photodetection can be dramatically enhanced when the thickness is reduced to several quintuple layers with a widely tunable band gap depending on the thickness.
Topological insulator
Gapless playback
Photodetection
Surface States
Cite
Citations (0)
Topological insulators (quantum spin Hall systems) are insulating in the bulk but have gapless edge/surface states, which remain gapless even when nonmagnetic disorder or interaction is present. This robustness stems from the topological nature characterized by the Z2 topological number, and this offers us various kinds of new novel properties. We review prominent advances in theories and in experiments on topological insulators since their theoretical proposal in 2005.
Topological insulator
Gapless playback
Cite
Citations (13)