771 research outputs found
Bulk-Fermi-Arc Transition Induced Large Photogalvanic Effect in Weyl Semimetals
The surface Fermi arc, as a hallmark of Weyl semimetals (WSMs), has been well
known in current research, but it remains a challenge to unveil novel phenomena
associated with the Fermi arc. Here, we predict a heretofore unrecognized
process in WSMs, namely, the photoinduced transition between the bulk states
and the Fermi arc. We find this process is significant and can lead to a large
effective three-dimensional shift current on the boundaries with the Fermi arc
in wide terahertz range. Moreover, due to the low symmetry of the boundaries,
the surface photogalvanic effect predicted here can appear in a large class of
WSMs that do not have bulk shift current. Hence, our work not only unveils a
hidden photogalvanic effect in WSMs but also suggests that all the WSMs are
promising material candidates for developing efficient terahertz
photodetectors.Comment: 6 pages, 5 figure
Planar Hall effect in topological Weyl and nodal line semimetals
Using symmetry analysis and semiclassical Boltzmann equation, we
theoretically explore the planar Hall effect (PHE) in three-dimensional
materials. We demonstrate that PHE is a general phenomenon that can occur in
various systems regardless of band topology. Both the Lorentz force and Berry
curvature effects can induce significant PHE, and the leading contributions of
both effects linearly depend on the electric and magnetic fields. The Lorentz
force and Berry curvature PHE coefficient possess only antisymmetric and
symmetric parts, respectively. Both contributions respect the same crystalline
symmetry constraints but differ under time-reversal symmetry. Remarkably, for
topological Weyl semimetal, the Berry curvature PHE coefficient is a constant
that does not depends on the Fermi energy, while the Lorentz force contribution
linearly increases with the Fermi energy, resulting from the linear dispersion
of the Weyl point. Furthermore, we find that the PHE in topological nodal line
semimetals is mainly induced by the Lorentz force, as the Berry curvature in
these systems vanishes near the nodal line. Our study not only highlights the
significance of the Lorentz force in PHE, but also reveals its unique
characteristics, which will be beneficial for determining the Lorentz force
contribution experimentally.Comment: 9 pages, 5 figure
Deep Learning the Effects of Photon Sensors on the Event Reconstruction Performance in an Antineutrino Detector
We provide a fast approach incorporating the usage of deep learning for
evaluating the effects of photon sensors in an antineutrino detector on the
event reconstruction performance therein. This work is an attempt to harness
the power of deep learning for detector designing and upgrade planning. Using
the Daya Bay detector as a benchmark case and the vertex reconstruction
performance as the objective for the deep neural network, we find that the
photomultiplier tubes (PMTs) have different relative importance to the vertex
reconstruction. More importantly, the vertex position resolutions for the Daya
Bay detector follow approximately a multi-exponential relationship with respect
to the number of PMTs and hence, the coverage. This could also assist in
deciding on the merits of installing additional PMTs for future detector plans.
The approach could easily be used with other objectives in place of vertex
reconstruction
Optical loss compensation in a bulk left-handed metamaterial by the gain in quantum dots
A bulk left-handed metamaterial with fishnet structure is investigated to
show the optical loss compensation via surface plasmon amplification, with the
assistance of a Gaussian gain in PbS quantum dots. The optical resonance
enhancement around 200 THz is confirmed by the retrieval method. By exploring
the dependence of propagation loss on the gain coefficient and metamaterial
thickness, we verify numerically that the left-handed response can endure a
large propagation thickness with ultralow and stable loss under a certain gain
coefficient.Comment: 6 pages with 4 figure
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