1,318 research outputs found
Linear magnetoconductivity in an intrinsic topological Weyl semimetal
Searching for the signature of the violation of chiral charge conservation in
solids has inspired a growing passion on the magneto-transport in topological
semimetals. One of the open questions is how the conductivity depends on
magnetic fields in a semimetal phase when the Fermi energy crosses the Weyl
nodes. Here, we study both the longitudinal and transverse magnetoconductivity
of a topological Weyl semimetal near the Weyl nodes with the help of a two-node
model that includes all the topological semimetal properties. In the semimetal
phase, the Fermi energy crosses only the 0th Landau bands in magnetic fields.
For a finite potential range of impurities, it is found that both the
longitudinal and transverse magnetoconductivity are positive and linear at the
Weyl nodes, leading to an anisotropic and negative magnetoresistivity. The
longitudinal magnetoconductivity depends on the potential range of impurities.
The longitudinal conductivity remains finite at zero field, even though the
density of states vanishes at the Weyl nodes. This work establishes a relation
between the linear magnetoconductivity and the intrinsic topological Weyl
semimetal phase.Comment: An extended version accepted by New. J. Phys. with 15 pages and 3
figure
Edge states and integer quantum Hall effect in topological insulator thin films
The integer quantum Hall effect is a topological state of quantum matter in
two dimensions, and has recently been observed in three-dimensional topological
insulator thin films. Here we study the Landau levels and edge states of
surface Dirac fermions in topological insulators under strong magnetic field.
We examine the formation of the quantum plateaux of the Hall conductance and
find two different patterns, in one pattern the filling number covers all
integers while only odd integers in the other. We focus on the quantum plateau
closest to zero energy and demonstrate the breakdown of the quantum spin Hall
effect resulting from structure inversion asymmetry. The phase diagrams of the
quantum Hall states are presented as functions of magnetic field, gate voltage
and chemical potential. This work establishes an intuitive picture of the edge
states to understand the integer quantum Hall effect for Dirac electrons in
topological insulator thin films.Comment: 10 pages, 5 figure
High-field magnetoconductivity of topological semimetals with short-range potential
Weyl semimetals are three-dimensional topological states of matter, in a
sense that they host paired monopoles and antimonopoles of Berry curvature in
momentum space, leading to the chiral anomaly. The chiral anomaly has long been
believed to give a positive magnetoconductivity or negative magnetoresistivity
in strong and parallel fields. However, several recent experiments on both Weyl
and Dirac topological semimetals show a negative magnetoconductivity in high
fields. Here, we study the magnetoconductivity of Weyl and Dirac semimetals in
the presence of short-range scattering potentials. In a strong magnetic field
applied along the direction that connects two Weyl nodes, we find that the
conductivity along the field direction is determined by the Fermi velocity,
instead of by the Landau degeneracy. We identify three scenarios in which the
high-field magnetoconductivity is negative. Our findings show that the
high-field positive magnetoconductivity may not be a compelling signature of
the chiral anomaly and will be helpful for interpreting the inconsistency in
the recent experiments and earlier theories.Comment: An extended version accepted by Phys. Rev. B, with 11 pages and 4
figure
Quality-Aware Network for Face Parsing
This is a very short technical report, which introduces the solution of the
Team BUPT-CASIA for Short-video Face Parsing Track of The 3rd Person in Context
(PIC) Workshop and Challenge at CVPR 2021.
Face parsing has recently attracted increasing interest due to its numerous
application potentials. Generally speaking, it has a lot in common with human
parsing, such as task setting, data characteristics, number of categories and
so on. Therefore, this work applies state-of-the-art human parsing method to
face parsing task to explore the similarities and differences between them. Our
submission achieves 86.84% score and wins the 2nd place in the challenge.Comment: 2nd place in Short-video Face Parsing Track of The 3rd Person in
Context (PIC) Workshop and Challenge at CVPR 202
Fine-mapping using the weighted average method for a case-control study
We present a new method for fine-mapping a disease susceptibility locus using a case-control design. The new method, termed the weighted average (WA) statistic, averages the Cochran-Armitage (CA) trend test statistic and the difference between the Hardy-Weinberg disequilibrium test statistic for cases and controls (the HWD trend). The main characteristics of the WA statistic are that it improves on the weaknesses, and maintains the strengths, of both the CA trend test and the HWD trend test. Data from three different populations in the Genetic Analysis Workshop 14 (GAW14) simulated dataset (Aipotu, Karangar, and Danacaa) were first subjected to model-free linkage analysis to find regions exhibiting linkage. Then, for fine-scale mapping, 140 SNPs within the significant linkage regions were analyzed with the WA test statistic on replicates of the three populations, both separately and combined. The regions that were significant in the multipoint linkage analysis were also significant in this fine-scale mapping. The most significant regions that were obtained using the WA statistic were regions in chromosome 3 (B03T3056–B03T3058, p-value < 1 × 10(-10 )) and chromosome 9 (B09T8332–B09T8334, p-value 1 × 10(-6 )). Based on the results of the simulated GAW14 data, the WA test statistic showed good performance and could narrow down the region containing the susceptibility locus. However, the strength of the signal depends on both the strength of the linkage disequilibrium and the heterozygosity of the linked marker
- …