33,130 research outputs found
Discovering new two-dimensional topological insulators from computational screening
We have performed a computational screening of topological two-dimensional
(2D) materials from the Computational 2D Materials Database (C2DB) employing
density functional theory. A full \textit{ab initio} scheme for calculating
hybrid Wannier functions directly from the Kohn-Sham orbitals has been
implemented and the method was used to extract indices, Chern
numbers and Mirror Chern numbers of 3331 2D systems including both
experimentally known and hypothetical 2D materials. We have found a total of 46
quantum spin Hall insulators, 7 quantum anomalous Hall insulators and 9
crystalline topological insulators that are all predicted to be dynamically
stable. Roughly one third of these were known prior to the screening. The most
interesting of the novel topological insulators are investigated in more
detail. We show that the calculated topological indices of the quantum
anomalous Hall insulators are highly sensitive to the approximation used for
the exchange-correlation functional and reliable predictions of the topological
properties of these materials thus require methods beyond density functional
theory. We also performed calculations, which yield a gap of 0.65 eV for
the quantum spin Hall insulator PdSe in the MoS crystal structure. This
is significantly higher than any known 2D topological insulator and three times
larger than the Kohn-Sham gap.Comment: 12 page
Topological Insulator in an Atomic Liquid
We demonstrate theoretically an atomic liquid phase that supports
topologically nontrivial electronic structure. A minimum two-orbital model of
liquid topological insulator in two dimensions is constructed within the
framework of tight-binding molecular dynamics. As temperature approaches zero,
our simulations show that the atoms crystallize into a triangular lattice with
nontrivial band topology at high densities. Thermal fluctuations at finite
temperatures melt the lattice, giving rise to a liquid state which inherits the
nontrivial topology from the crystalline phase. The electronic structure of the
resultant atomic liquid is characterized by a nonzero Bott index. Our work
broadens the notion of topological materials, and points to a new systematic
approach for searching topological phases in amorphous and liquid systems.Comment: 5 pages, 4 figure
Weaving quantum optical frequency combs into continuous-variable hypercubic cluster states
Cluster states with higher-dimensional lattices that cannot be physically
embedded in three-dimensional space have important theoretical interest in
quantum computation and quantum simulation of topologically ordered
condensed-matter systems. We present a simple, scalable, top-down method of
entangling the quantum optical frequency comb into hypercubic-lattice
continuous-variable cluster states of a size of about 10^4 quantum field modes,
using existing technology. A hypercubic lattice of dimension D (linear, square,
cubic, hypercubic, etc.) requires but D optical parametric oscillators with
bichromatic pumps whose frequency splittings alone determine the lattice
dimensionality and the number of copies of the state.Comment: 8 pages, 5 figures, submitted for publicatio
Random volumes from matrices
We propose a class of models which generate three-dimensional random volumes,
where each configuration consists of triangles glued together along multiple
hinges. The models have matrices as the dynamical variables and are
characterized by semisimple associative algebras A. Although most of the
diagrams represent configurations which are not manifolds, we show that the set
of possible diagrams can be drastically reduced such that only (and all of the)
three-dimensional manifolds with tetrahedral decompositions appear, by
introducing a color structure and taking an appropriate large N limit. We
examine the analytic properties when A is a matrix ring or a group ring, and
show that the models with matrix ring have a novel strong-weak duality which
interchanges the roles of triangles and hinges. We also give a brief comment on
the relationship of our models with the colored tensor models.Comment: 33 pages, 31 figures. Typos correcte
Entanglement branching operator
We introduce an entanglement branching operator to split a composite
entanglement flow in a tensor network which is a promising theoretical tool for
many-body systems. We can optimize an entanglement branching operator by
solving a minimization problem based on squeezing operators. The entanglement
branching is a new useful operation to manipulate a tensor network. For
example, finding a particular entanglement structure by an entanglement
branching operator, we can improve a higher-order tensor renormalization group
method to catch a proper renormalization flow in a tensor network space. This
new method yields a new type of tensor network states. The second example is a
many-body decomposition of a tensor by using an entanglement branching
operator. We can use it for a perfect disentangling among tensors. Applying a
many-body decomposition recursively, we conceptually derive projected entangled
pair states from quantum states that satisfy the area law of entanglement
entropy.Comment: 11 pages, 13 figure
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