7,115 research outputs found
Two-Dimensional Transition Metal Dichalcogenides with a Hexagonal Lattice: Room Temperature Quantum Spin Hall Insulators
So far, several transition metal dichalcogenides (TMDCs) based
two-dimensional (2D) topological insulators (TIs) have been discovered, all of
them based on a tetragonal lattice. However, in 2D crystals, the hexagonal
rather than the tetragonal symmetry is the most common motif. Here, based on
first-principles calculations, we propose a new class of stable 2D TMDCs of
composition MX2 (M=Mo, W, X=S, Se, Te) with a hexagonal lattice. They are all
in the same stability range as other 2D TMDC allotropes that have been
demonstrated experimentally, and they are identified to be practical 2D TIs
with large band gaps ranging from 41 to 198 meV, making them suitable for
applications at room-temperature. Besides, in contrast to tetragonal 2D TMDs,
their hexagonal lattice will greatly facilitate the integration of theses novel
TI states van-der-Waals crystals with other hexagonal or honeycomb materials,
and thus provide a route for 2D-material-based devices for wider nanoelectronic
and spintronic applications. The nontrivial band gaps of both WSe2 and WTe2 2D
crystals are 198 meV, which are larger than that in any previously reported
TMDC-based TIs. These large band gaps entirely stem from the strong spin-orbit
coupling strength within the d orbitals of Mo/W atoms near the Fermi level. Our
findings will significantly broaden the scientific and technological impact of
both 2D TIs and TMDCs
Topological superfluid in a fermionic bilayer optical lattice
In this paper, a topological superfluid phase with Chern number C=1
possessing gapless edge states and non-Abelian anyons is designed in a C=1
topological insulator proximity to an s-wave superfluid on an optical lattice
with the effective gauge field and layer-dependent Zeeman field coupled to
ultracold fermionic atoms pseudo spin. We also study its topological properties
and calculate the phase stiffness by using the random-phase-approximation
approach. Finally we derive the temperature of the Kosterlitz-Thouless
transition by means of renormalized group theory. Owning to the existence of
non-Abelian anyons, this C=1 topological superfluid may be a possible candidate
for topological quantum computation.Comment: 15 pages, 8 figure
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