6,626 research outputs found
Photon-assisted electron transmission resonance through a quantum well with spin-orbit coupling
Using the effective-mass approximation and Floquet theory, we study the
electron transmission over a quantum well in semiconductor heterostructures
with Dresselhaus spin-orbit coupling and an applied oscillation field. It is
demonstrated by the numerical evaluations that Dresselhaus spin-orbit coupling
eliminates the spin degeneracy and leads to the splitting of asymmetric
Fano-type resonance peaks in the conductivity. In turn, the splitting of
Fano-type resonance induces the spin- polarization-dependent electron-current.
The location and line shape of Fano-type resonance can be controlled by
adjusting the oscillation frequency and the amplitude of external field as
well. These interesting features may be a very useful basis for devising
tunable spin filters.Comment: 10pages,4figure
Sequential Optimization for Efficient High-Quality Object Proposal Generation
We are motivated by the need for a generic object proposal generation
algorithm which achieves good balance between object detection recall, proposal
localization quality and computational efficiency. We propose a novel object
proposal algorithm, BING++, which inherits the virtue of good computational
efficiency of BING but significantly improves its proposal localization
quality. At high level we formulate the problem of object proposal generation
from a novel probabilistic perspective, based on which our BING++ manages to
improve the localization quality by employing edges and segments to estimate
object boundaries and update the proposals sequentially. We propose learning
the parameters efficiently by searching for approximate solutions in a
quantized parameter space for complexity reduction. We demonstrate the
generalization of BING++ with the same fixed parameters across different object
classes and datasets. Empirically our BING++ can run at half speed of BING on
CPU, but significantly improve the localization quality by 18.5% and 16.7% on
both VOC2007 and Microhsoft COCO datasets, respectively. Compared with other
state-of-the-art approaches, BING++ can achieve comparable performance, but run
significantly faster.Comment: Accepted by TPAM
Model Hamiltonian for Topological Insulators
In this paper we give the full microscopic derivation of the model
Hamiltonian for the three dimensional topological insulators in the
family of materials (, and ). We first give a
physical picture to understand the electronic structure by analyzing atomic
orbitals and applying symmetry principles. Subsequently, we give the full
microscopic derivation of the model Hamiltonian introduced by Zhang {\it et al}
[\onlinecite{zhang2009}] based both on symmetry principles and the perturbation theory. Two different types of terms, which
break the in-plane full rotation symmetry down to three fold rotation symmetry,
are taken into account. Effective Hamiltonian is derived for the topological
surface states. Both the bulk and the surface models are investigated in the
presence of an external magnetic field, and the associated Landau level
structure is presented. For more quantitative fitting to the first principle
calculations, we also present a new model Hamiltonian including eight energy
bands.Comment: 18 pages, 9 figures, 5 table
Hierarchical Classification of Research Fields in the "Web of Science" Using Deep Learning
This paper presents a hierarchical classification system that automatically
categorizes a scholarly publication using its abstract into a three-tier
hierarchical label set (discipline, field, subfield) in a multi-class setting.
This system enables a holistic categorization of research activities in the
mentioned hierarchy in terms of knowledge production through articles and
impact through citations, permitting those activities to fall into multiple
categories. The classification system distinguishes 44 disciplines, 718 fields
and 1,485 subfields among 160 million abstract snippets in Microsoft Academic
Graph (version 2018-05-17). We used batch training in a modularized and
distributed fashion to address and allow for interdisciplinary and interfield
classifications in single-label and multi-label settings. In total, we have
conducted 3,140 experiments in all considered models (Convolutional Neural
Networks, Recurrent Neural Networks, Transformers). The classification accuracy
is > 90% in 77.13% and 78.19% of the single-label and multi-label
classifications, respectively. We examine the advantages of our classification
by its ability to better align research texts and output with disciplines, to
adequately classify them in an automated way, and to capture the degree of
interdisciplinarity. The proposed system (a set of pre-trained models) can
serve as a backbone to an interactive system for indexing scientific
publications in the future.Comment: Under review in QS
Quantum Anomalous Hall Effect in HgMnTe Quantum Wells
The quantum Hall effect is usually observed when the two-dimensional electron
gas is subjected to an external magnetic field, so that their quantum states
form Landau levels. In this work we predict that a new phenomenon, the quantum
anomalous Hall effect, can be realized in HgMnTe quantum wells,
without the external magnetic field and the associated Landau levels. This
effect arises purely from the spin polarization of the atoms, and the
quantized Hall conductance is predicted for a range of quantum well thickness
and the concentration of the atoms. This effect enables dissipationless
charge current in spintronics devices.Comment: 5 pages, 3 figures. For high resolution figures see final published
version when availabl
ELUCID - Exploring the Local Universe with reConstructed Initial Density field III: Constrained Simulation in the SDSS Volume
A method we developed recently for the reconstruction of the initial density
field in the nearby Universe is applied to the Sloan Digital Sky Survey Data
Release 7. A high-resolution N-body constrained simulation (CS) of the
reconstructed initial condition, with particles evolved in a 500 Mpc/h
box, is carried out and analyzed in terms of the statistical properties of the
final density field and its relation with the distribution of SDSS galaxies. We
find that the statistical properties of the cosmic web and the halo populations
are accurately reproduced in the CS. The galaxy density field is strongly
correlated with the CS density field, with a bias that depend on both galaxy
luminosity and color. Our further investigations show that the CS provides
robust quantities describing the environments within which the observed
galaxies and galaxy systems reside. Cosmic variance is greatly reduced in the
CS so that the statistical uncertainties can be controlled effectively even for
samples of small volumes.Comment: submitted to ApJ, 19 pages, 22 figures. Please download the
high-resolution version at http://staff.ustc.edu.cn/~whywang/paper
Electron interaction-driven insulating ground state in Bi2Se3 topological insulators in the two dimensional limit
We report a transport study of ultrathin Bi2Se3 topological insulators with
thickness from one quintuple layer to six quintuple layers grown by molecular
beam epitaxy. At low temperatures, the film resistance increases
logarithmically with decreasing temperature, revealing an insulating ground
state. The sharp increase of resistance with magnetic field, however, indicates
the existence of weak antilocalization, which should reduce the resistance as
temperature decreases. We show that these apparently contradictory behaviors
can be understood by considering the electron interaction effect, which plays a
crucial role in determining the electronic ground state of topological
insulators in the two dimensional limit.Comment: 4 figure
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