Density of Surface States in 3D Topological Insulators in the Presence of Magnetic Field with Hexagonal Warping Effect (original) (raw)
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Physical Review B, 2015
The response of thin films of Bi2Se3 to a strong perpendicular magnetic field is investigated by performing magnetic bandstructure calculations for a realistic multi-band tight-binding model. Several crucial features of Landau quantization in a realistic three-dimensional topological insulator are revealed. The n = 0 Landau level is absent in ultra-thin films, in agreement with experiment. In films with a crossover thickness of five quintuple layers, there is a signature of the n = 0 level, whose overall trend as a function of magnetic field matches the established low-energy effectivemodel result. Importantly, we find a field-dependent splitting and a strong spin-polarization of the n = 0 level which can be measured experimentally at reasonable field strengths. Our calculations show mixing between the surface and bulk Landau levels which causes the character of levels to evolve with magnetic field.
Scientific reports, 2014
A hexagonal warping term has been proposed recently to explain the experimentally observed 2D equal energy contours of the surface states of the topological insulator Bi2Te3. Differing from the Dirac fermion Hamiltonian, the hexagonal warping term leads to the opening up of a band gap by an in-plane magnetization. We study the transmission between two Bi2Te3 segments subjected to different in-plane magnetizations and potentials. The opening up of a bandgap, and the accompanying displacement and distortion of the constant energy surfaces from their usual circular shapes by the in-plane magnetizations, modify the transverse momentum overlap between the two Bi2Te3 segments, and strongly modulate the transmission profile. The strong dependence of the TI surface state transport of Bi2Te3 on the magnetization orientation of an adjacent ferromagnetic layer may potentially be utilized in, e.g., a memory readout application.
On the origin of two-dimensional electron gas states at the surface of topological insulators
Jetp Letters, 2011
The study of three dimensional topological insula tors is a rapidly developing field of physics. The surface of this type of materials has a metallic character, whereas the bulk is an insulator. The conducting prop erties of the surface originate from the strong spinorbit coupling, which leads to the formation of spin split topological surface states that have Dirac type dispersion. These states are protected from scattering on defects by the time reversal symmetry, which gives a potential possibility of using them in new spintronic devices.
Spin dynamics of 3d and 4d impurities embedded in prototypical topological insulators
Physical Review Materials
Topological insulators are insulating bulk materials hosting conducting surface states. Their magnetic doping breaks time-reversal symmetry and generates numerous interesting effects such as dissipationless transport. Nonetheless, their dynamical properties are still poorly understood. Here, we perform a systematic investigation of transverse spin excitations of 3d and 4d single impurities embedded in two prototypical topological insulators (Bi 2 Te 3 and Bi 2 Se 3). The impurityinduced states within the bulk gap of the topological insulators are found to have a drastic impact on the spin excitation spectra, resulting in very high lifetimes reaching up to microseconds. An intuitive picture of the spin dynamics is obtained by mapping onto a generalized Landau-Lifshitz-Gilbert phenomenological model. The first quantity extracted from this mapping procedure is the magnetic anisotropy energy, which is then compared to the one provided by the magnetic force theorem. This uncovers some difficulties encountered with the latter, which can provide erroneous results for impurities with a high density of states at the Fermi energy. Moreover, the Gilbert damping and nutation tensors are obtained. The nutation effects can lead to a non-negligible shift in the spin excitation resonance in the high-frequency regime. Finally, we study the impact of the surface state on the spin dynamics, which may be severely altered due to the repositioning of the impurity-induced state in comparison to the bulk case. Our systematic investigation of this series of magnetic impurities sheds light on their spin dynamics within topological insulators, with implications for available and future experimental studies as, for instance, on the viability of using such impurities for solid-state qubits.
Physical Review B, 2013
The magnetic proximity effect is a fundamental feature of heterostructures composed of layers of topological insulators and magnetic materials since it underlies many potential applications in devices with novel quantum functionality. Within density functional theory we study magnetic proximity effect at the 3D topological insulator/magnetic insulator (TI/MI) interface in Bi 2 Se 3 /MnSe(111) system as an example. We demonstrate that a gapped ordinary bound state which spectrum depends on the interface potential arises in the immediate region of the interface. The gapped topological Dirac state also arises in the system owing to relocation to deeper atomic layers of topological insulator. The gap in the Dirac cone is originated from an overlapping of the topological and ordinary interfacial states. This result being also corroborated by the analytic model, is a key aspect of the magnetic proximity effect mechanism in the TI/MI structures.
2011
We study the effect of electron-electron interaction on the surface resistivity of three-dimensional (3D) topological insulators. In the absence of umklapp scattering, the existence of the Fermi-liquid (T 2) term in resistivity of a two-dimensional (2D) metal depends on the Fermi surface geometry, in particular, on whether it is convex or concave. On doping, the Fermi surface of 2D metallic surface states in 3D topological insulators of the Bi2Te3 family changes its shape from convex to concave due to hexagonal warping, while still being too small to allow for umklapp scattering. We show that the T 2 term in the resistivity is present only in the concave regime and demonstrate that the resistivity obeys a universal scaling form valid for an arbitrary 2D Fermi surface near a convex/concave transition.
Topological Surface States in Three-Dimensional Magnetic Insulators
Physical Review Letters, 2008
An electron moving in a magnetically ordered background feels an effective magnetic field that can be both stronger and more rapidly varying than typical externally applied fields. One consequence is that insulating magnetic materials in three dimensions can have topologically nontrivial properties of the effective band structure. For the simplest case of two bands, these "Hopf insulators" are characterized by a topological invariant as in quantum Hall states and Z2 topological insulators, but instead of a Chern number or parity, the underlying invariant is the Hopf invariant that classifies maps from the 3-sphere to the 2-sphere. This paper gives an efficient algorithm to compute whether a given magnetic band structure has nontrivial Hopf invariant, a double-exchange-like tight-binding model that realizes the nontrivial case, and a numerical study of the surface states of this model. PACS numbers: 73.20.At, 03.65.Vf Recent theoretical and experimental work has shown that there exist nonmagnetic band insulators in which spin-orbit coupling plays a role similar to that of the magnetic field in the integer quantum Hall effect (IQHE). In two dimensions [1], these "topological insulators" have robust edge states, observed in HgTe/(Hg,Cd)Te heterostructures , and are predicted to show a spin quantum Hall effect. The existence of a genuinely threedimensional topological insulator phase [3, 4, 5] with protected surface states, recently observed in Bi 0.9 Sb 0.1 [6], is rather surprising because the IQHE does not have a fully three-dimensional version, but only layered versions of the 2D case. Both 2D and 3D topological insulators are nonmagnetic, and in fact unbroken time-reversal invariance is required for the edge state to remain gapless. The edge or surface states of topological insulators and IQHE states exist because there are topological invariants that distinguish these insulating states from ordinary insulators, and across a boundary between one of these states and an ordinary insulator, the energy gap must close.
Physical Review B, 2011
We report a transport study of ultrathin Bi 2 Se 3 topological insulators with thickness from one quintuple layer to six quintuple layers grown by molecular beam epitaxy. At low temperatures, the film resistance increases logarithmically with decreasing temperature, revealing an insulating ground state. The sharp increase of resistance with magnetic field, however, indicates the existence of weak antilocalization, which should reduce the resistance as temperature decreases. We show that these apparently contradictory behaviors can be understood by considering the electron interaction effect, which plays a crucial role in determining the electronic ground state of topological insulators in the two dimensional limit.
Three-Dimensional Topological Insulators
2010
Topological insulators in three dimensions are nonmagnetic insulators that possess metallic surface states as a consequence of the nontrivial topology of electronic wavefunctions in the bulk of the material. They are the first known examples of topological order in bulk solids.
Effect of Dilute Magnetism in a Topological Insulator
Frontiers in Materials
Three-dimensional (3D) topological insulator (TI) has emerged as a unique state of quantum matter and generated enormous interests in condensed matter physics. The surfaces of a 3D TI consist of a massless Dirac cone, which is characterized by the Z2 topological invariant. Introduction of magnetism on the surface of a TI is essential to realize the quantum anomalous Hall effect and other novel magneto-electric phenomena. Here, by using a combination of first-principles calculations, magneto-transport and angle-resolved photoemission spectroscopy (ARPES), we study the electronic properties of gadolinium (Gd)-doped Sb2Te3. Our study shows that Gd doped Sb2Te3 is a spin-orbit-induced bulk band-gap material, whose surface is characterized by a single topological surface state. Our results provide a new platform to investigate the interactions between dilute magnetism and topology in magnetic doped topological materials.