The IrTe2 transition metal dichalcogenide undergoes a series of structural and electronic phase transitions when doped with Pt. The nature of each phase and the mechanism of the phase transitions have attracted much attention. In this paper, we repor
t scanning tunneling microscopy and spectroscopy studies of Pt doped IrTe2 with varied Pt contents. In pure IrTe2, we find that the ground state has a 1/6 superstructure, and the electronic structure is inconsistent with Fermi surface nesting induced charge density wave order. Upon Pt doping, the crystal structure changes to a 1/5 superstructure and then to a quasi-periodic hexagonal phase. First principles calculations show that the superstructures and electronic structures are determined by the global chemical strain and local impurity states that can be tuned systematically by Pt doping.
The interaction between magnetic impurities and the gapless surface state is of critical importance for realizing novel quantum phenomena and new functionalities in topological insulators. By combining angle-resolved photoemission spectroscopic exper
iments with density functional theory calculations, we show that surface deposition of Cr atoms on Bi$_2$Se$_3$ does not lead to gap opening of the surface state at the Dirac point, indicating the absence of long-range out-of-plane ferromagnetism down to our measurement temperature of 15 K. This is in sharp contrast to bulk Cr doping, and the origin is attributed to different Cr occupation sites. These results highlight the importance of nanoscale configuration of doped magnetic impurities in determining the electronic and magnetic properties of topological insulators.
We predict from first-principles calculations a novel structure of stanene with dumbbell units (DB), and show that it is a two-dimensional topological insulator with inverted band gap which can be tuned by compressive strain. Furthermore, we propose
that the boron nitride sheet and reconstructed ($2times2$) InSb(111) surfaces are ideal substrates for the experimental realization of DB stanene, maintaining its non-trivial topology. Combined with standard semiconductor technologies, such as magnetic doping and electrical gating, the quantum anomalous Hall effect, Chern half metallicity and topological superconductivity can be realized in DB stanene on those substrates. These properties make the two-dimensional supported stanene a good platform for the study of new quantum spin Hall insulator as well as other exotic quantum states of matter.
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.
The electronic structure of the recently synthesised (3x3) reconstructed silicene on (4x4) Ag(111) is investigated by first-principles calculations. New states emerge due to the strong hybridization between silicene and Ag. Analyzing the nature and c
omposition of these hybridized states, we show that i) it is possible to clearly distinguish them from states coming from the Dirac cone of free-standing silicene or from the sp-bands of bulk Ag and ii) assign their contribution to the description of the linearly dispersing band observed in photoemission. Furthermore, we show that silicene atoms contribute to the Fermi level, which leads to similar STM patterns as observed below or above the Fermi level. Our findings are crucial for the proper interpretation of experimental observations.
