Peizhe Tang

Topology-Driven Magnetic Quantum Phase Transition in Topological Insulators

Simultaneous topological and magnetic quantum phase transitions are observed in thin films of Bi2(SexTe1-x)3 doped with chromium Topological insulators owe their exotic properties to the peculiarities of their band structure, and one can induce a transition between a topologically trivial and nontrivial material by chemical doping. Now, J. Zhang et al. (p. 1582) have gone a step further—simultaneously observing that a magnetic quantum transition as the ratio of Se and Te is varied in Bi2(SexTe1-x)3 thin films grown by molecular beam epitaxy and doped with magnetic Cr. Photoemission and transport experiments, as well as density functional calculations, imply that the topological transition induces magnetism The breaking of time reversal symmetry in topological insulators may create previously unknown quantum effects. We observed a magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 topological insulator films grown by means of molecular beam epitaxy. Across the critical point, a topological quantum phase transition is revealed through both angle-resolved photoemission measurements and density functional theory calculations. We present strong evidence that the bulk band topology is the fundamental driving force for the magnetic quantum phase transition. The tunable topological and magnetic properties in this system are well suited for realizing the exotic topological quantum phenomena in magnetic topological insulators.

Electronic structure of silicene on Ag(111): Strong hybridization effects

We acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG–Proposal No. 267374), Spanish Grants (FIS2010-21282-C02-01 and PIB2010US-00652), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT-578-13), and European Commission project CRONOS (280879-2 CRONOS CP-FP7). Computational time was granted by i2basque and BSC Red Espanola de Supercomputacion. M.A. thanks CONACYT for the Ph.D. fellowship and the financial support of project REA-FP7-IRSES TEMM1P (GA 295172).

Large-gap quantum spin Hall states in decorated stanene grown on a substrate

Two-dimensional stanene is a promising candidate material for realizing room-temperature quantum spin Hall (QSH) effect. Monolayer stanene has recently been fabricated by molecular beam epitaxy, but shows metallic features on Bi

Dirac fermions in an antiferromagnetic semimetal

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Weak topological insulators induced by the interlayer coupling: A first-principles study of stacked Bi2TeI

Te

Design of strain-engineered quantum tunneling devices for topological surface states

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Robust gapless surface state and Rashba-splitting bands upon surface deposition of magnetic Cr on Bi2Se3.

(111) substrate, which motivates us to study the important influence of substrate. Based on first-principles calculations, we find that varying substrate conditions considerably tunes electronic properties of stanene. The supported stanene gives either trivial or QSH states, with significant Rashba splitting induced by inversion asymmetry. More importantly, large-gap (up to 0.3 eV) QSH states are realizable when growing stanene on various substrates, like the anion-terminated (111) surfaces of SrTe, PbTe, BaSe and BaTe. These findings provide significant guidance for future research of stanene and large-gap QSH states.

Sulfur immobilization and lithium storage on defective graphene: A first-principles study

The prediction of an antiferromagnetic semimetal that breaks both time-reversal and inversion symmetry but respects their combination could provide a platform for studying the interplay between Dirac fermions and magnetism. Analogues of the elementary particles have been extensively searched for in condensed-matter systems for both scientific interest and technological applications1,2,3. Recently, massless Dirac fermions were found to emerge as low-energy excitations in materials now known as Dirac semimetals4,5,6. All of the currently known Dirac semimetals are non-magnetic with both time-reversal symmetry and inversion symmetry 7,8,9. Here we show that Dirac fermions can exist in one type of antiferromagnetic system, where both and are broken but their combination is respected. We propose orthorhombic antiferromagnet CuMnAs as a candidate, analyse the robustness of the Dirac points under symmetry protections and demonstrate its distinctive bulk dispersions, as well as the corresponding surface states, by ab initio calculations. Our results provide a possible platform to study the interplay of Dirac fermion physics and magnetism.

Electronic and magnetic properties of boron nitride nanoribbons with topological line defects

Based on first-principles calculations, we predict Bi2TeI, a stoichiometric compound synthesized, to be a weak topological insulator (TI) in layered subvalent bismuth telluroiodides. Within a bulk energy gap of 80 meV, two Dirac-cone-like topological surface states exist on the side surface perpendicular to BiTeI layer plane. These Dirac cones are relatively isotropic due to the strong inter-layer coupling, distinguished from those of previously reported weak TI candidates. Moreover, with chemically stable cladding layers, the BiTeI-Bi2-BiTeI sandwiched structure is a robust quantum spin Hall system, which can be obtained by simply cleaving the bulk Bi2TeI.

Band Engineering of Dirac Surface States in Topological-Insulator-Based van der Waals Heterostructures.

Strain-dependent charge and spin transport on a topological insulator (TI) surface are investigated by combining first-principles calculations with quantum tunneling theory. It is shown that the Dirac point of helical surface states can be significantly shifted by applying compressive uniaxial strain. As an example of strain engineering applications based on this effect, a strain-induced quantum tunneling nanostructure is designed, where the tunneling conductance and the spin texture of surface states can be sensitively modulated by strain. Our work suggests that various local strain patterns can be integrated to manipulate surface states in all-TI-based spintronic nanodevices.