42 research outputs found
On the electronic structure of silicene on Ag substrate: strong hybridization effects
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 composition 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.Comment: 8 pages, 3 figures including supplementary materia
Weak topological insulators induced by the inter-layer coupling: A first-principles study of stacked Bi2TeI
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.Comment: 4.5 pages, 4 figure
Topological Phase Transitions Induced by Disorder in Magnetically Doped (Bi, Sb)Te Thin Films
We study disorder induced topological phase transitions in magnetically doped
(Bi, Sb)Te thin films, by using large scale transport simulations of
the conductance through a disordered region coupled to reservoirs in the
quantum spin Hall regime. Besides the disorder strength, the rich phase diagram
also strongly depends on the magnetic exchange field, the Fermi level, and the
initial topological state in the undoped and clean limit of the films. In an
initially trivial system at non-zero exchange field, varying the disorder
strength can induce a sequence of transitions from a normal insulating, to a
quantum anomalous Hall, then a spin-Chern insulating, and finally an Anderson
insulating state. While for a system with topology initially, a similar
sequence, but only starting from the quantum anomalous Hall state, can be
induced. Varying the Fermi level we find a similarly rich phase diagram,
including transitions from the quantum anomalous Hall to the spin-Chern
insulating state via a state that behaves as a mixture of a quantum anomalous
Hall and a metallic state, akin to recent experimental reports
Large-gap quantum spin Hall insulators in tin films
The search of large-gap quantum spin Hall (QSH) insulators and effective
approaches to tune QSH states is important for both fundamental and practical
interests. Based on first-principles calculations we find two-dimensional tin
films are QSH insulators with sizable bulk gaps of 0.3 eV, sufficiently large
for practical applications at room temperature. These QSH states can be
effectively tuned by chemical functionalization and by external strain. The
mechanism for the QSH effect in this system is band inversion at the \Gamma
point, similar to the case of HgTe quantum well. With surface doping of
magnetic elements, the quantum anomalous Hall effect could also be realized
Visualizing topological edge states of single and double bilayer Bi supported on multibilayer Bi(111) films
Freestanding single-bilayer Bi(111) is a two-dimensional topological
insulator with edge states propagating along its perimeter. Given the
interlayer coupling experimentally, the topological nature of Bi(111) thin
films and the impact of the supporting substrate on the topmost Bi bilayer are
still under debate. Here, combined with scanning tunneling microscopy and
first-principles calculations, we systematically study the electronic
properties of Bi(111) thin films grown on a NbSe2 substrate. Two types of
non-magnetic edge structures, i.e., a conventional zigzag edge and a 2x1
reconstructed edge, coexist alternately at the boundaries of single bilayer
islands, the topological edge states of which exhibit remarkably different
energy and spatial distributions. Prominent edge states are persistently
visualized at the edges of both single and double bilayer Bi islands,
regardless of the underlying thickness of Bi(111) thin films. We provide an
explanation for the topological origin of the observed edge states that is
verified with first-principles calculations. Our paper clarifies the
long-standing controversy regarding the topology of Bi(111) thin films and
reveals the tunability of topological edge states via edge modifications.Comment: 36 pages, 10 figure