2,018 research outputs found
Observation of Landau level-like quantizations at 77 K along a strained-induced graphene ridge
Recent studies show that the electronic structures of graphene can be
modified by strain and it was predicted that strain in graphene can induce
peaks in the local density of states (LDOS) mimicking Landau levels (LLs)
generated in the presence of a large magnetic field. Here we report scanning
tunnelling spectroscopy (STS) observation of nine strain-induced peaks in LDOS
at 77 K along a graphene ridge created when the graphene layer was cleaved from
a sample of highly oriented pyrolytic graphite (HOPG). The energies of these
peaks follow the progression of LLs of massless 'Dirac fermions' (DFs) in a
magnetic field of 230 T. The results presented here suggest a possible route to
realize zero-field quantum Hall-like effects at 77 K
Analysis of Quality Influencing Factors and Coping Strategies in Site Construction Stage of Prefabricated Building
Limited to the current industry, the personnel, knowledge, and technology reserves of prefabricated buildings are not sufficient, which directly affects the engineering quality of prefabricated buildings. In particular, the quality control of the prefabricated building site construction stage is the most critical. In view of the on-site construction stage of prefabricated buildings, this paper sorts out the influencing factors of project quality from three aspects of personnel, technology and management, and from the three aspects of personnel quality, construction technology and whole process management, the coping strategies of engineering quality problems are put forward. It can effectively improve the detailed management and control of quality problems in the construction stage of the prefabricated building, and help the rapid development of the prefabricated building industry
Spherical Transformer: Adapting Spherical Signal to CNNs
Convolutional neural networks (CNNs) have been widely used in various vision
tasks, e.g. image classification, semantic segmentation, etc. Unfortunately,
standard 2D CNNs are not well suited for spherical signals such as panorama
images or spherical projections, as the sphere is an unstructured grid. In this
paper, we present Spherical Transformer which can transform spherical signals
into vectors that can be directly processed by standard CNNs such that many
well-designed CNNs architectures can be reused across tasks and datasets by
pretraining. To this end, the proposed method first uses locally structured
sampling methods such as HEALPix to construct a transformer grid by using the
information of spherical points and its adjacent points, and then transforms
the spherical signals to the vectors through the grid. By building the
Spherical Transformer module, we can use multiple CNN architectures directly.
We evaluate our approach on the tasks of spherical MNIST recognition, 3D object
classification and omnidirectional image semantic segmentation. For 3D object
classification, we further propose a rendering-based projection method to
improve the performance and a rotational-equivariant model to improve the
anti-rotation ability. Experimental results on three tasks show that our
approach achieves superior performance over state-of-the-art methods
Quantum Transports in Two-Dimensions with Long Range Hopping: Shielding, Localization and the Extended Isolated State
We investigate the effects of disorder and shielding on quantum transports in
a two dimensional system with all-to-all long range hopping. In the weak
disorder, cooperative shielding manifests itself as perfect conducting channels
identical to those of the short range model, as if the long range hopping does
not exist. With increasing disorder, the average and fluctuation of conductance
are larger than those in the short range model, since the shielding is
effectively broken and therefore long range hopping starts to take effect. Over
several orders of disorder strength (until times of nearest
hopping), although the wavefunctions are not fully extended, they are also
robustly prevented from being completely localized into a single site. Each
wavefunction has several localization centers around the whole sample, thus
leading to a fractal dimension remarkably smaller than 2 and also remarkably
larger than 0, exhibiting a hybrid feature of localization and delocalization.
The size scaling shows that for sufficiently large size and disorder strength,
the conductance tends to saturate to a fixed value with the scaling function
, which is also a marginal phase between the typical metal
() and insulating phase (). The all-to-all coupling expels
one isolated but extended state far out of the band, whose transport is
extremely robust against disorder due to absence of backscattering. The bond
current picture of this isolated state shows a quantum version of short circuit
through long hopping.Comment: 15 pages, 8 figure
Electronic Structures of Graphene Layers on Metal Foil: Effect of Point Defects
Here we report a facile method to generate a high density of point defects in
graphene on metal foil and show how the point defects affect the electronic
structures of graphene layers. Our scanning tunneling microscopy (STM)
measurements, complemented by first principle calculations, reveal that the
point defects result in both the intervalley and intravalley scattering of
graphene. The Fermi velocity is reduced in the vicinity area of the defect due
to the enhanced scattering. Additionally, our analysis further points out that
periodic point defects can tailor the electronic properties of graphene by
introducing a significant bandgap, which opens an avenue towards all-graphene
electronics.Comment: 4 figure
Strain Induced One-Dimensional Landau-Level Quantization in Corrugated Graphene
Theoretical research has predicted that ripples of graphene generates
effective gauge field on its low energy electronic structure and could lead to
zero-energy flat bands, which are the analog of Landau levels in real magnetic
fields. Here we demonstrate, using a combination of scanning tunneling
microscopy and tight-binding approximation, that the zero-energy Landau levels
with vanishing Fermi velocities will form when the effective pseudomagnetic
flux per ripple is larger than the flux quantum. Our analysis indicates that
the effective gauge field of the ripples results in zero-energy flat bands in
one direction but not in another. The Fermi velocities in the perpendicular
direction of the ripples are not renormalized at all. The condition to generate
the ripples is also discussed according to classical thin-film elasticity
theory.Comment: 4 figures, Phys. Rev.
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