204 research outputs found
Accurate theoretical prediction on positron lifetime of bulk materials
Based on the first-principles calculations, we perform an initiatory
statistical assessment on the reliability level of theoretical positron
lifetime of bulk material. We found the original generalized gradient
approximation (GGA) form of the enhancement factor and correlation potentials
overestimates the effect of the gradient factor. Furthermore, an excellent
agreement between model and data with the difference being the noise level of
the data is found in this work. In addition, we suggest a new GGA form of the
correlation scheme which gives the best performance. This work demonstrates
that a brand-new reliability level is achieved for the theoretical prediction
on positron lifetime of bulk material and the accuracy of the best theoretical
scheme can be independent on the type of materials.Comment: 9 pages, 2 figure, 3 table
Weak-value amplification forWeyl-point separation in momentum space
The existence of Weyl nodes in the momentum space is a hallmark of a Weyl
semimetal (WSM). A WSM can be confirmed by observing its Fermi arcs with
separated Weyl nodes. In this paper, we study the spin- orbit interaction of
light on the surface of WSM in the limit that the thickness is ultra-thin and
the incident surface does not support Fermi arc. Our results show that the
spin-dependent splitting induced by the spin-orbit interaction is related to
the separation of Weyl nodes. By proposing an amplification technique called
weak measurements, the distance of the nodes can be precisely determined. This
system may have application in characterizing other parameters of WSM.Comment: 8 pages, 8 figure
Giant quantized Goos-H\"anchen effect on the surface of graphene in quantum Hall regime
We theoretically predict a giant quantized Goos-H\"{a}nchen (GH) effect on
the surface of graphene in quantum Hall regime. The giant quantized GH effect
manifests itself as an angular shift whose quantized step reaches the order of
mrad for light beams impinging on a graphene-on-substrate system. The quantized
GH effect can be attributed to quantized Hall conductivity, which corresponds
to the discrete Landau levels in quantum Hall regime. We find that the
quantized step can be greatly enhanced for incident angles near the Brewster
angle. Moreover, the Brewster angle is sensitive to the Hall conductivity, and
therefore the quantized GH effect can be modulated by the Fermi energy and the
external magnetic field. The giant quantized GH effect offers a convenient way
to determine the quantized Hall conductivity and the discrete Landau levels by
a direct optical measurement.Comment: 6 pages, 6 figure
Partial regularity of harmonic maps from Alexandrov spaces
In this paper, we prove the Lipschitz regularity of continuous harmonic maps
from an finite dimensional Alexandrov space to a compact smooth Riemannian
manifold. This solves a conjecture of F. H. Lin in \cite{lin97}. The proof
extends the argument of Huang-Wang \cite {hua-w10}
GO-FEAP: Global Optimal UAV Planner Using Frontier-Omission-Aware Exploration and Altitude-Stratified Planning
Autonomous exploration is a fundamental problem for various applications of
unmanned aerial vehicles(UAVs). Existing methods, however, are demonstrated to
static local optima and two-dimensional exploration. To address these
challenges, this paper introduces GO-FEAP (Global Optimal UAV Planner Using
Frontier-Omission-Aware Exploration and Altitude-Stratified Planning), aiming
to achieve efficient and complete three-dimensional exploration.
Frontier-Omission-Aware Exploration module presented in this work takes into
account multiple pivotal factors, encompassing frontier distance, nearby
frontier count, frontier duration, and frontier categorization, for a
comprehensive assessment of frontier importance. Furthermore, to tackle
scenarios with substantial vertical variations, we introduce the
Altitude-Stratified Planning strategy, which stratifies the three-dimensional
space based on altitude, conducting global-local planning for each stratum. The
objective of global planning is to identify the most optimal frontier for
exploration, followed by viewpoint selection and local path optimization based
on frontier type, ultimately generating dynamically feasible three-dimensional
spatial exploration trajectories. We present extensive benchmark and real-world
tests, in which our method completes the exploration tasks with unprecedented
completeness compared to state-of-the-art approaches.Comment: 7 pages,29 figure
Large Magnetoresistance and Weak Antilocalization in V1-delta Sb2 Single Crystal
The binary pnictide semimetals have attracted considerable attention due to
their fantastic physical properties that include topological effects, negative
magnetoresistance, Weyl fermions and large non-saturation magnetoresistance. In
this paper, we have successfully grown the high-quality V1-deltaSb2 single
crystals by Sb flux method and investigated their electronic transport
properties. A large positive magnetoresistance that reaches 477% under a
magnetic field of 12 T at T = 1.8 K was observed. Notably, the
magnetoresistance showed a cusp-like feature at the low magnetic fields and
such feature weakened gradually as the temperature increased, which indicated
the presence of weak antilocalization effect (WAL). The angle-dependent
magnetoconductance and the ultra-large prefactor alpha extracted from the
Hikami-Larkin-Nagaoka equation revealed that the WAL effect is a 3D bulk effect
originated from the three-dimensional bulk spin-orbital coupling.Comment: 18 pages,5 figures, 1 tabl
Probing the Chiral Anomaly by Planar Hall Effect in Three-dimensional Dirac Semimetal Cd3As2 Nanoplates
Searching for exotic transport properties in new topological state of matters
is an active topic. One of the most fascinating achievements is the chiral
anomaly in recently discovered Weyl semimetals (WSMs), which is manifested as a
negative longitudinal magnetoresistance (LMR) in the presence of a magnetic
field B parallel to an electric field E. Another predicted key effect closely
related to the chiral anomaly is the planar Hall effect (PHE), which has not
been identified in WSMs so far. Here we carried out the planar Hall
measurements on Cd3As2 nanoplates, and found that, accompanied by the large
negative LMR, a PHE with non-zero transverse voltage can be developed while
tilting the in-plane magnetic field B away from the electric field E. Further
experiments reveal that both the PHE and the negative LMR can be suppressed
synchronously by increasing the temperature, but still visible at room
temperature, indicating the same origin of these two effects. The observation
of PHE in Cd3As2 nanoplates gives another transport evidence for the chiral
anomaly and provides a deep insight into the chiral charge pumping in Weyl
Fermions system.Comment: 17 pages, 4 figure
de Haas-van Alphen study on three-dimensional topological semimetal pyrite PtBi2
We present the systematic de Haas-van Alphen (dHvA) quantum oscillations
studies on the recently discovered topological Dirac semimetal pyrite PtBi2
single crystals. Remarkable dHvA oscillations were observed at field as low as
1.5 T. From the analyses of dHvA oscillations, we have extracted high quantum
mobility, light effective mass and phase shift factor for Dirac fermions in
pyrite PtBi2. From the angular dependence of dHvA oscillations, we have mapped
out the topology of the Fermi surface and identified additional oscillation
frequencies which were not probed by SdH oscillations.Comment: 11pages, 4 figure
Giant photonic spin Hall effect near the Dirac points
The origin of spin-orbit interaction of light at a conventional optical
interface lies in the transverse nature of the photon polarization: The
polarizations associated with the plane-wave components experience slightly
different rotations in order to satisfy the transversality after reflection or
refraction. Recent advances in topological photonic materials provide crucial
opportunities to reexamine the spin-orbit interaction of light at the unique
optical interface. Here, we establish a general model to describe the
spin-orbit interaction of light in the photonic Dirac metacrystal. We find a
giant photonic spin Hall effect near the Dirac points when a Gaussian beam
impinges at the interface of the photonic Dirac metacrystal. The giant photonic
spin Hall effect is attribute to the strong spin-orbit interaction of light,
which manifests itself as the large polarization rotations of different
plane-wave components. We believe that these results may provide insight into
the fundamental properties of the spin-orbit interaction of light in the
topological photonic systems.Comment: 7 pages, 5 figure
Graphene-analogues boron nitride nanosheets confining ionic liquids: a high-performance quasi-liquid solid electrolyte
Solid electrolytes are one of the most promising electrolyte systems for safe lithium batteries, but the low ionic conductivity of these electrolytes seriously hinders the development of efficient lithium batteries. Here, a novel class of graphene-analogues boron nitride (g-BN) nanosheets confining an ultrahigh concentration of ionic liquids (ILs) in an interlayer and out-of-layer chamber to give rise to a quasi-liquid solid electrolyte (QLSE) is reported. The electron-insulated g-BN nanosheet host with a large specific surface area can confine ILs as much as 10 times of the host's weight to afford high ionic conductivity (3.85 × 10−3 S cm−1 at 25 °C, even 2.32 × 10−4 S cm−1 at −20 °C), which is close to that of the corresponding bulk IL electrolytes. The high ionic conductivity of QLSE is attributed to the enormous absorption for ILs and the confining effect of g-BN to form the ordered lithium ion transport channels in an interlayer and out-of-layer of g-BN. Furthermore, the electrolyte displays outstanding electrochemical properties and battery performance. In principle, this work enables a wider tunability, further opening up a new field for the fabrication of the next-generation QLSE based on layered nanomaterials in energy conversion devices
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