High-quality Sb₂Te₃ films are obtained by molecular beam epitaxy on a graphene substrate and investigated by in situ scanning tunneling microscopy and spectroscopy. Intrinsic defects responsible for the natural p-type conductivity of Sb₂Te₃ are identified to be the Sb vacancies and Sb_Te antisites in...

[Phys. Rev. Lett. 108, 066809] Published Fri Feb 10, 2012

We study the Dirac quasiparticles in d-dimensional lattice systems of electrons in the presence of domain walls (d=1), vortices (d=2), or hedgehogs (d=3) of superconducting and/or insulating, order parameters, which appear as mass terms in the Dirac equation. Such topological defects have been known...

[Phys. Rev. B 85, 085304] Published Fri Feb 10, 2012

The surface of W(110) exhibits a Dirac-cone-like state with d character within a spin-orbit-induced symmetry gap. As a function of the wave vector parallel to the surface, it shows a nearly massless energy dispersion and a pronounced spin polarization, which is antisymmetric with respect to the Bril...

[Phys. Rev. Lett. 108, 066808] Published Fri Feb 10, 2012

We study a generic two-dimensional hopping model on a honeycomb lattice with strong spin-orbit coupling, without the requirement that the half-filled lattice be a topological insulator. For quarter-(or three-quarter) filling, we show that a state with a quantized Hall conductance generically arises ...

[Phys. Rev. B 85, 073103] Published Thu Feb 09, 2012

We study the properties of topological phases by calculating the ground-state degeneracy (GSD) of the two-dimensional Levin-Wen (LW) model. Here it is explicitly shown that the GSD depends only on the spatial topology of the system. Then we show that the ground state on a sphere is always nondegener...

[Phys. Rev. B 85, 075107] Published Tue Feb 07, 2012

Defects that appear in heterostructure junctions involving topological insulators are sources of gapless modes governing the low-energy properties of the systems, as recently elucidated by Teo and Kane [ Phys. Rev. B 82 115120 (2010)]. A standard approach for the calculation of topological invarian...

[Phys. Rev. B 85, 085409] Published Mon Feb 06, 2012

We report a high-pressure single crystal study of the topological superconductor Cu_xBi₂Se₃. Resistivity measurements under pressure show superconductivity is depressed smoothly. At the same time the metallic behavior is gradually lost. The upper-critical field data B_c2(T) under pressure collapse ont...

[Phys. Rev. Lett. 108, 057001] Published Tue Jan 31, 2012

We examine how the properties of the Kondo insulators change when the symmetry of the underlying crystal field multiplets is taken into account. We employ the Anderson lattice model and consider its low-energy physics. We show that in a large class of crystal field configurations, Kondo insulators c...

[Phys. Rev. B 85, 045130] Published Mon Jan 30, 2012

We study the possibility of realizing quantum anomalous Hall (QAH) effect with tunable Chern number through doping magnetic elements in a multilayer topological insulator film. We find that high Chern number QAH phases exist in ideal neutral samples and can make transition to another QAH phase direc...

[Phys. Rev. B 85, 045445] Published Mon Jan 30, 2012

We propose an experimental scheme to simulate and detect the properties of time-reversal invariant topological insulators, using cold atoms trapped in one-dimensional bichromatic optical lattices. This system is described by a one-dimensional Aubry-Andre model with an additional SU(2) gauge structur...

[Phys. Rev. A 85, 013638] Published Fri Jan 27, 2012

We present a theoretical study of electron-phonon scattering effects in thin films made of a strong topological insulator. The phonons are modeled by isotropic elastic continuum theory with stress-free boundary conditions, and the interaction with the helical surface Dirac fermions is mediated by th...

[Phys. Rev. B 85, 035441] Published Wed Jan 25, 2012

We construct a simple model for electrons in a three-dimensional crystal where a combination of short-range hopping and spin-orbit coupling results in nearly flat bands characterized by a nontrivial Z₂ topological index. The flat band is separated from other bands by a band gap Δ that is much larger...

[Phys. Rev. B 85, 041104] Published Wed Jan 25, 2012

We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi₂Se₃. We observed circular dichroism (CD) as large as 30% in the ARPES data ...

[Phys. Rev. Lett. 108, 046805] Published Wed Jan 25, 2012

We provide a self-consistent mean-field framework to study the effect of strong interactions in a quantum spin Hall insulator on the honeycomb lattice. We identify an exotic phase for large spin-orbit coupling and intermediate Hubbard interaction. This phase is gapped and does not break any symmetry...

[Phys. Rev. Lett. 108, 046401] Published Wed Jan 25, 2012

Noncollinear magnetic order is typically characterized by a tetrad ground state manifold (GSM) of three perpendicular vectors or nematic directors. We study three types of tetrad orders in two spatial dimensions, whose GSMs are SO(3)=S³/Z₂, S³/Z₄, and S³/Q₈, respectively. Q₈ denotes the non-Abelian ...

[Phys. Rev. Lett. 108, 047202] Published Wed Jan 25, 2012

We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum,...

[Phys. Rev. Lett. 108, 036803] Published Thu Jan 19, 2012

We report transport studies on magnetically doped Bi₂Se₃ topological insulator ultrathin films grown by molecular beam epitaxy. The magnetotransport behavior exhibits a systematic crossover between weak antilocalization and weak localization with the change of magnetic impurity concentration, temper...

[Phys. Rev. Lett. 108, 036805] Published Thu Jan 19, 2012

We investigate transport properties of the surface states of three-dimensional topological insulator thin films in the presence of an electrostatic potential γ and a spin-splitting Zeeman field g. It is shown that there exist a quantum pseudospin Hall phase, a quantum anomalous Hall phase, and a com...

[Phys. Rev. B 85, 045118] Published Wed Jan 18, 2012

It has been proposed that disorder may lead to a new type of topological insulator, called the topological Anderson insulator (TAI). Here we examine the physical origin of this phenomenon. We calculate the topological invariants and density of states of the disordered model in a supercell of a two-d...

[Phys. Rev. B 85, 035107] Published Thu Jan 12, 2012

We consider the superconducting proximity effect in a helical Luttinger liquid at the edge of a two-dimensional (2D) topological insulator, and derive the low-energy Hamiltonian for an edge state tunnel-coupled to an s-wave superconductor. In addition to correlations between the left- and right-movi...

[Phys. Rev. B 85, 035310] Published Thu Jan 12, 2012

We study nontrivial responses of topological superconductors and superfluids to the temperature gradient and rotation of the system. In two-dimensional gapped systems, the Strěda formula for the electric Hall conductivity is generalized to the thermal Hall conductivity. Applying this formula to the ...

[Phys. Rev. Lett. 108, 026802] Published Thu Jan 12, 2012

The effective 6×6 matrix Hamiltonian for two-dimensional states in HgTe/CdTe quantum wells is derived. The use of the extended basis (in contrast to the previously studied 4×4 matrix Hamiltonian) allows us to describe quantum wells with arbitrary orientation of interfaces and investigate the influen...

[Phys. Rev. B 85, 045310] Published Wed Jan 11, 2012

Nodal noncentrosymmetric superconductors have topologically nontrivial properties manifested by protected zero-energy surface states. Specifically, it was recently found that zero-energy surface flat bands of topological origin appear at their surface. We show that the presence of certain inversion-...

[Phys. Rev. B 85, 024522] Published Wed Jan 11, 2012

Topological insulators are insulating in the bulk but possess metallic surface states protected by time-reversal symmetry. Here, we report on a detailed electronic transport study in high-quality Bi₂Se₃ topological insulator thin films contacted by superconducting (In, Al, and W) electrodes. The res...

[Phys. Rev. B 85, 045415] Published Tue Jan 10, 2012

Graphene and three-dimensional topological insulators are well-known Dirac materials whose bulk and surface states are governed by Dirac equations. They not only show good transport properties but also carry various quanta related to the geometrical phase such as charge, spin, and valley Hall conduc...

[Phys. Rev. B 85, 045307] Published Mon Jan 09, 2012

We propose a realization of the Weyl semimetal phase that is invariant under time reversal and occurs due to broken inversion symmetry. We consider both a simple superlattice model and a more realistic tight-binding model describing an experimentally reasonable HgTe/CdTe multilayer structure. The tw...

[Phys. Rev. B 85, 035103] Published Mon Jan 09, 2012

One of the defining properties of the conventional three-dimensional (“Z₂” or “spin-orbit”) topological insulator is its characteristic magnetoelectric effect, as described by axion electrodynamics. In this paper, we discuss an analog of such a magnetoelectric effect in the thermal (or gravitational...

[Phys. Rev. B 85, 045104] Published Thu Jan 05, 2012

Within the semiclassical approach, we calculate contributions of the Berry phase and of the Zeeman coupling of an electron moment with the magnetic field to the phase of the Shubnikov–de Haas oscillations for the surface electrons in the Bi₂X₃ family of three-dimensional topological insulators (X st...

[Phys. Rev. B 85, 033301] Published Wed Jan 04, 2012

We report the experimental observation of Landau quantization of molecular beam epitaxy grown Sb₂Te₃ thin films by a low-temperature scanning tunneling microscope. Different from all the reported systems, the Landau quantization in a Sb₂Te₃ topological insulator is not sensitive to the intrinsic sub...

[Phys. Rev. Lett. 108, 016401] Published Tue Jan 03, 2012

Point contact conductance measurements on topological Bi₂Te₂Se and Bi₂Se₃ films reveal a signature of superconductivity below 2–3 K. In particular, critical current dips and a robust zero-bias conductance peak are observed. The latter suggests the presence of zero-energy bound states that could be a...

[Phys. Rev. B 84, 224521] Published Thu Dec 29, 2011