25,888 research outputs found
Topological semimetals with Riemann surface states
Riemann surfaces are geometric constructions in complex analysis that may
represent multi-valued holomorphic functions using multiple sheets of the
complex plane. We show that the energy dispersion of surface states in
topological semimetals can be represented by Riemann surfaces generated by
holomorphic functions in the two-dimensional momentum space, whose constant
height contours correspond to Fermi arcs. This correspondence is demonstrated
in the recently discovered Weyl semimetals and leads us to predict new types of
topological semimetals, whose surface states are represented by double- and
quad-helicoid Riemann surfaces. The intersection of multiple helicoids, or the
branch cut of the generating function, appears on high-symmetry lines in the
surface Brillouin zone, where surface states are guaranteed to be doubly
degenerate by a glide reflection symmetry. We predict the heterostructure
superlattice [(SrIrO)(CaIrO)] to be a topological semimetal
with double-helicoid Riemann surface states.Comment: Four pages, four figures and two pages of appendice
Controllable Goos-H\"{a}nchen shifts and spin beam splitter for ballistic electrons in a parabolic quantum well under a uniform magnetic field
The quantum Goos-H\"{a}nchen shift for ballistic electrons is investigated in
a parabolic potential well under a uniform vertical magnetic field. It is found
that the Goos-H\"{a}nchen shift can be negative as well as positive, and
becomes zero at transmission resonances. The beam shift depends not only on the
incident energy and incidence angle, but also on the magnetic field and Landau
quantum number. Based on these phenomena, we propose an alternative way to
realize the spin beam splitter in the proposed spintronic device, which can
completely separate spin-up and spin-down electron beams by negative and
positive Goos-H\"{a}nchen shifts.Comment: 6 pages, 6 figure
Topological magnetoplasmon
Classical wave fields are real-valued, ensuring the wave states at opposite
frequencies and momenta to be inherently identical. Such a particle-hole
symmetry can open up new possibilities for topological phenomena in classical
systems. Here we show that the historically studied two-dimensional (2D)
magnetoplasmon, which bears gapped bulk states and gapless one-way edge states
near zero frequency, is topologically analogous to the 2D topological p+\Ii p
superconductor with chiral Majorana edge states and zero modes. We further
predict a new type of one-way edge magnetoplasmon at the interface of opposite
magnetic domains, and demonstrate the existence of zero-frequency modes bounded
at the peripheries of a hollow disk. These findings can be readily verified in
experiment, and can greatly enrich the topological phases in bosonic and
classical systems.Comment: 12 pages, 6 figures, 1 supporting materia
Renewable Composite Quantile Method and Algorithm for Nonparametric Models with Streaming Data
We are interested in renewable estimations and algorithms for nonparametric
models with streaming data. In our method, the nonparametric function of
interest is expressed through a functional depending on a weight function and a
conditional distribution function (CDF). The CDF is estimated by renewable
kernel estimations combined with function interpolations, based on which we
propose the method of renewable weighted composite quantile regression (WCQR).
Then we fully use the model structure and obtain new selectors for the weight
function, such that the WCQR can achieve asymptotic unbiasness when estimating
specific functions in the model. We also propose practical bandwidth selectors
for streaming data and find the optimal weight function minimizing the
asymptotic variance. The asymptotical results show that our estimator is almost
equivalent to the oracle estimator obtained from the entire data together.
Besides, our method also enjoys adaptiveness to error distributions, robustness
to outliers, and efficiency in both estimation and computation. Simulation
studies and real data analyses further confirm our theoretical findings.Comment: 24 pages, 0 figure
Diversified Texture Synthesis with Feed-forward Networks
Recent progresses on deep discriminative and generative modeling have shown
promising results on texture synthesis. However, existing feed-forward based
methods trade off generality for efficiency, which suffer from many issues,
such as shortage of generality (i.e., build one network per texture), lack of
diversity (i.e., always produce visually identical output) and suboptimality
(i.e., generate less satisfying visual effects). In this work, we focus on
solving these issues for improved texture synthesis. We propose a deep
generative feed-forward network which enables efficient synthesis of multiple
textures within one single network and meaningful interpolation between them.
Meanwhile, a suite of important techniques are introduced to achieve better
convergence and diversity. With extensive experiments, we demonstrate the
effectiveness of the proposed model and techniques for synthesizing a large
number of textures and show its applications with the stylization.Comment: accepted by CVPR201
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