35,218 research outputs found
3D quantum Hall effect of Fermi arcs in topological semimetals
The quantum Hall effect is usually observed in 2D systems. We show that the
Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological
semimetals. Because of the topological constraint, the Fermi arc at a single
surface has an open Fermi surface, which cannot host the quantum Hall effect.
Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at
opposite surfaces can form a complete Fermi loop and support the quantum Hall
effect. The edge states of the Fermi arcs show a unique 3D distribution, giving
an example of (d-2)-dimensional boundary states. This is distinctly different
from the surface-state quantum Hall effect from a single surface of topological
insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall
conductivity evolves from the 1/B dependence to quantized plateaus at the Weyl
nodes. This behavior can be realized by tuning gate voltages in a slab of
topological semimetal, such as the TaAs family, CdAs, or NaBi. This
work will be instructive not only for searching transport signatures of the
Fermi arcs but also for exploring novel electron gases in other topological
phases of matter.Comment: 5 pages, 3 figure
Automatic Bootstrapping and Tracking of Object Contours
This work introduces a new fully automatic object tracking and segmentation framework. The framework consists of a motion based bootstrapping algorithm concurrent to a shape based active contour. The shape based active contour uses a finite shape memory that is automatically and continuously built from both the bootstrap process and the active contour object tracker. A scheme is proposed to ensure the finite shape memory is continuously updated but forgets unnecessary information. Two new ways of automatically extracting shape information from image data given a region of interest are also proposed. Results demonstrate that the bootstrapping stage provides important motion and shape information to the object tracker
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