66 research outputs found
Probing the order parameter symmetry of two-dimensional superconductors by twisted Josephson interferometry
Probing the superconducting order parameter symmetry is a crucial step
towards understanding the pairing mechanism in unconventional superconductors.
Inspired by the recent discoveries of superconductivity in various van der
Waals materials, and the availability of the relative twist angle as a
continuous tuning knob in these systems, we propose a general setup for probing
the order parameter symmetry of two-dimensional superconductors in twisted
Josephson junctions. The junction is composed of an anisotropic s-wave
superconductor as a probe and another superconductor with an unknown order
parameter symmetry. Assuming momentum-resolved tunneling, we investigate
signatures of different order parameter symmetries in the twist angle
dependence of the critical current, the current-phase relations, and magnetic
field dependence. As a concrete example, we study a twisted Josephson junction
between NbSe2 and magic angle twisted bilayer graphene.Comment: 15 pages, 5 figure
Chirality driven topological electronic structure of DNA-like materials
Topological aspects of the geometry of DNA and similar chiral molecules have
received a lot of attention, while the topology of their electronic structure
is less explored. Previous experiments have revealed that DNA can efficiently
filter spin-polarized electrons between metal contacts, a process called
chiral-induced spin-selectivity (CISS). However, the underlying correlation
between chiral structure and electronic spin remains elusive. In this work, we
reveal an orbital texture in the band structure, a topological characteristic
induced by the chirality. We find that this orbital texture enables the chiral
molecule to polarize the quantum orbital. This orbital polarization effect
(OPE) induces spin polarization assisted by the spin-orbit interaction from a
metal contact and leads to magnetorestistance and chiral separation. The
orbital angular momentum of photoelectrons also plays an essential role in
related photoemission experiments. Beyond CISS, we predict that OPE can induce
spin-selective phenomena even in achiral but inversion-breaking materials.Comment: 24 pages, 4 figures, and Supplementary Material
Low-complexity Resource Allocation for User Paired RSMA in Future 6G Wireless Networks
Rate-splitting multiple access (RSMA) uplink requires optimization of
decoding order and power allocation, while decoding order is a discrete
variable, and it is very complex to find the optimal decoding order if the
number of users is large enough. This letter proposes a low-complexity user
pairing-based resource allocation algorithm with the objective of minimizing
the maximum latency, which significantly reduces the computational complexity
and also achieves similar performance to unpaired uplink RSMA. A closed-form
expression for power and bandwidth allocation is first derived, and then a
bisection method is used to determine the optimal resource allocation. Finally,
the proposed algorithm is compared with unpaired RSMA, paired NOMA and unpaired
NOMA. The results demonstrate the effectiveness of the proposed algorithm
Joint Perceptual Learning for Enhancement and Object Detection in Underwater Scenarios
Underwater degraded images greatly challenge existing algorithms to detect
objects of interest. Recently, researchers attempt to adopt attention
mechanisms or composite connections for improving the feature representation of
detectors. However, this solution does \textit{not} eliminate the impact of
degradation on image content such as color and texture, achieving minimal
improvements. Another feasible solution for underwater object detection is to
develop sophisticated deep architectures in order to enhance image quality or
features. Nevertheless, the visually appealing output of these enhancement
modules do \textit{not} necessarily generate high accuracy for deep detectors.
More recently, some multi-task learning methods jointly learn underwater
detection and image enhancement, accessing promising improvements. Typically,
these methods invoke huge architecture and expensive computations, rendering
inefficient inference. Definitely, underwater object detection and image
enhancement are two interrelated tasks. Leveraging information coming from the
two tasks can benefit each task. Based on these factual opinions, we propose a
bilevel optimization formulation for jointly learning underwater object
detection and image enhancement, and then unroll to a dual perception network
(DPNet) for the two tasks. DPNet with one shared module and two task subnets
learns from the two different tasks, seeking a shared representation. The
shared representation provides more structural details for image enhancement
and rich content information for object detection. Finally, we derive a
cooperative training strategy to optimize parameters for DPNet. Extensive
experiments on real-world and synthetic underwater datasets demonstrate that
our method outputs visually favoring images and higher detection accuracy
Learning Heavily-Degraded Prior for Underwater Object Detection
Underwater object detection suffers from low detection performance because
the distance and wavelength dependent imaging process yield evident image
quality degradations such as haze-like effects, low visibility, and color
distortions. Therefore, we commit to resolving the issue of underwater object
detection with compounded environmental degradations. Typical approaches
attempt to develop sophisticated deep architecture to generate high-quality
images or features. However, these methods are only work for limited ranges
because imaging factors are either unstable, too sensitive, or compounded.
Unlike these approaches catering for high-quality images or features, this
paper seeks transferable prior knowledge from detector-friendly images. The
prior guides detectors removing degradations that interfere with detection. It
is based on statistical observations that, the heavily degraded regions of
detector-friendly (DFUI) and underwater images have evident feature
distribution gaps while the lightly degraded regions of them overlap each
other. Therefore, we propose a residual feature transference module (RFTM) to
learn a mapping between deep representations of the heavily degraded patches of
DFUI- and underwater- images, and make the mapping as a heavily degraded prior
(HDP) for underwater detection. Since the statistical properties are
independent to image content, HDP can be learned without the supervision of
semantic labels and plugged into popular CNNbased feature extraction networks
to improve their performance on underwater object detection. Without bells and
whistles, evaluations on URPC2020 and UODD show that our methods outperform
CNN-based detectors by a large margin. Our method with higher speeds and less
parameters still performs better than transformer-based detectors. Our code and
DFUI dataset can be found in
https://github.com/xiaoDetection/Learning-Heavily-Degraed-Prior
Monopole-like orbital-momentum locking and the induced orbital transport in topological chiral semimetals
The interplay between chirality and topology nurtures many exotic electronic
properties. For instance, topological chiral semimetals display multifold
chiral fermions that manifest nontrivial topological charge and spin texture.
They are an ideal playground for exploring chirality-driven exotic physical
phenomena. In this work, we reveal a monopole-like orbital-momentum locking
texture on the three-dimensional Fermi surfaces of topological chiral
semimetals with B20 structures (e.g., RhSi and PdGa). This orbital texture
enables a large orbital Hall effect (OHE) and a giant orbital magnetoelectric
(OME) effect in the presence of current flow. Different enantiomers exhibit the
same OHE which can be converted to the spin Hall effect by spin-orbit coupling
in materials. In contrast, the OME effect is chirality-dependent and much
larger than its spin counterpart. Our work reveals the crucial role of orbital
texture for understanding OHE and OME effects in topological chiral semimetals
and paves the path for applications in orbitronics, spintronics, and enantiomer
recognition.Comment: 23 pages, 5 figure
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