194 research outputs found
Building topological device through emerging robust helical surface states
We propose a nonlocal manipulation method to build topological devices
through emerging robust helical surface states in Z_2=0 topological systems.
Specifically, in a ribbon of Z_2=0 Bernevig- Hughes-Zhang (BHZ) model with
finite-size effect, if magnetic impurities are doped on the top (bottom) edge,
the edge states on the bottom (top) edge can be altered according to the
strengths and directions of these magnetic impurities. Consequently, the
backscattering between the emerging robust helical edge states and gapped
normal edge states due to finite-size confinement is also changed, which makes
the system alternate between a perfect one-channel conductor and a perfect
insulator. This effect allows us to fabricate topological devices with high
on-off ratio. Moreover, it can also be generalized to 3D model and more
realistic Cd3As2 type Dirac semimetals.Comment: 7 pages, 6 figure
Source Delay in Mobile Ad Hoc Networks
Source delay, the time a packet experiences in its source node, serves as a
fundamental quantity for delay performance analysis in networks. However, the
source delay performance in highly dynamic mobile ad hoc networks (MANETs) is
still largely unknown by now. This paper studies the source delay in MANETs
based on a general packet dispatching scheme with dispatch limit (PD-
for short), where a same packet will be dispatched out up to times by its
source node such that packet dispatching process can be flexibly controlled
through a proper setting of . We first apply the Quasi-Birth-and-Death (QBD)
theory to develop a theoretical framework to capture the complex packet
dispatching process in PD- MANETs. With the help of the theoretical
framework, we then derive the cumulative distribution function as well as mean
and variance of the source delay in such networks. Finally, extensive
simulation and theoretical results are provided to validate our source delay
analysis and illustrate how source delay in MANETs are related to network
parameters.Comment: 11page
One-dimensional quantum channel in a graphene line defect
Using a tight-binding model, we study a line defect in graphene where a bulk
energy gap is opened by sublattice symmetry breaking. It is found that
sublattice symmetry breaking may induce many configurations that correspond to
different band spectra. In particular, a gapless state is observed for a
configuration which hold a mirror symmetry with respect to the line defect. We
find that this gapless state originates from the line defect and is independent
of the width of the graphene ribbon, the location of the line defect, and the
potentials in the edges of the ribbon. In particular, the gapless state can be
controlled by the gate voltage embedded below the line defect. Finally, this
result is supported with conductance calculations. This study shows how a
quantum channel could be constructed using a line defect, and how the quantum
channel can be controlled by tuning the gate voltage embedded below the line
defect.Comment: 8 pages, 10 figure
The First IEEE UV2022 Mathematical Modelling Competition: Backgrounds and Problems
Economic growth, people's health, and urban development face challenges in
the post-epidemic era. How to promote high-quality and sustainable urban
development, improve citizens' sense of happiness, and solve problems in city
management have become a heated and crucial topic. Mathematical modeling is a
research method that uses mathematical symbols to express practical problems,
establish mathematical models, and then propose solutions. The 1 IEEE
UV2022 Mathematical Modelling Competition is a satellite activity of the
6 IEEE International Conference on Universal Village, which expects
participants to use mathematical modeling methods for practical problems and
provide guidelines for sustainable social progress. This short paper introduces
the background of the competition and publishes the problems to be solved
Disorder and metal-insulator transitions in Weyl semimetals
The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has
Weyl nodes in bulk excitations and Fermi arcs surface states. We study the
effects of disorder and localization in WSMs and find three exotic phase
transitions. (I) Two Weyl nodes near the Brillouin zone boundary can be
annihilated pairwise by disorder scattering, resulting in the opening of a
topologically nontrivial gap and a transition from a WSM to a three-dimensional
(3D) quantum anomalous Hall state. (II) When the two Weyl nodes are well
separated in momentum space, the emergent bulk extended states can give rise to
a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (III)
Two Weyl nodes can emerge near the zone center when an insulating gap closes
with increasing disorder, enabling a direct transition from a normal band
insulator to a WSM. We determine the phase diagram by numerically computing the
localization length and the Hall conductivity, and propose that the exotic
phase transitions can be realized on a photonic lattice.Comment: 7 pages with appendix, 6 figure
Decoding flat bands from compact localized states
The flat band system is an ideal quantum platform to investigate the
kaleidoscope created by the electron-electron correlation effects. The central
ingredient of realizing a flat band is to find its compact localized states. In
this work, we develop a systematic way to generate the compact localized states
by designing destructive interference pattern from 1-dimensional chains. A
variety of 2-dimensional new flat band systems are constructed with this
method. Furthermore, we show that the method can be extended to generate the
compact localized states in multi-orbital systems by carefully designing the
block hopping scheme, as well as in quasicrystal and disorder systems
Disorder induced field effect transistor in bilayer and trilayer graphene
We propose use of disorder to produce a field effect transistor (FET) in
biased bilayer and trilayer graphene. Modulation of the bias voltage can
produce large variations in the conductance when the disorder's effects are
confined to only one of the graphene layers. This effect is based on the bias
voltage's ability to select which of the graphene layers carries current, and
is not tied to the presence of a gap in the density of states. In particular,
we demonstrate this effect in models of gapless ABA-stacked trilayer graphene,
gapped ABC-stacked trilayer graphene, and gapped bilayer graphene.Comment: 21 pages, 7 figure
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