arXiv subjects

Luyang Wang

Publications and source records attributed to Luyang Wang.

At least 19 recordsLinked to original sources

arXiv2026

NTIRE 2026 Low-light Enhancement: Twilight Cowboy Challenge

This paper presents a review of the NTIRE 2026 Low-light Enhancement: Twilight Cowboy Challenge. The objective of the competition was to merge a set of misaligned smartphone images in the raw domain, captured in low-light conditions, into a single, clean image. Introduced setup simultaneously addresses two problems of low-light photography: visual degradations such as high noise and mixed scene illuminants, and the geometric inconsistencies caused by hand movement during multi-frame capture. To advance research in low-light and nighttime computational photography, a challenging dataset was collected comprising 585 real-world scenes, spanning indoor low-light and outdoor nighttime conditions, for training and benchmarking participant solutions. The competition employed a three-stage evaluation protocol: automatic validation via the CodaBench platform in stages one and two, followed by blind assessment on a private test set for the final ranking. Ten teams surpassed the established baseline, achieving improvements of up to +6.49 dB in PSNR and +0.0101 in SSIM, thereby establishing new state-of-the-art performance for burst-based low-light image enhancement. These results demonstrate significant progress in handling real-world noise, motion, and illumination variability in the low-light setting. Comprehensive results, leaderboards, and additional information are publicly available at https://nightimaging.org.

cs.CV↗

arXiv2025

Three-Family Supersymmetric Pati-Salam Flux Models from Rigid D-Branes

Intersecting D-brane model building often suffer from the unstabilized open-string moduli, leading to the unwanted massless adjoint scalars. In our previous work arXiv:2505.03664, this issue was resolved by employing the rigid D6-branes on the $\mathbb{T}^6/(\mathbb{Z}_2 \times \mathbb{Z}_2^\prime)$ orientifold with discrete torsion, where fractional cycles eliminate all adjoint scalars. In this paper, we construct new three-family flux models in the Type IIB setup on $\mathbb{T}^6/(\mathbb{Z}_2 \times \mathbb{Z}_2)$, T-dual to the Type IIA rigid D6-brane construction with discrete torsion, by introducing the quantized background $G_3$ flux that stabilizes the closed-string complex structure moduli and axio-dilaton. The resulting Pati-Salam gauge symmetry can be spontaneously broken down to the Standard Model via a supersymmetry-preserving Higgs mechanism. All the consistency conditions, including $\mathcal{N}=1$ supersymmetry, RR tadpole cancellation, and K-theory constraints, are satisfied. We present the complete particle spectra for these models and discuss how exotic states dynamically decouple through strong dynamics in the hidden sector.

hep-th↗

arXiv2025

Quasiparticles and optical conductivity in the mixed state of Weyl superconductors with unconventional pairing

Previous investigations have revealed that the Weyl superconductor (WeylSC), realized in a superconductor-topological insulator heterostructure, can exhibit the Landau levels (LLs) of Bogoliubov quasiparticles in the presence of a vortex lattice. Here, we investigate the low-energy quasiparticle (QP) excitations in the mixed state of heterostructure WeylSCs with unconventional pairing. We find that the spin-singlet $d$-wave pairing induces flat Dirac-LLs of Bogoliubov QPs, whereas the excitation spectra for the spin-triplet chiral $p$-wave pairing show noticeable dispersion, except for the chiral symmetry-protected, dispersionless, zeroth Landau level (ZLL). Distinct QP excitations in the vortex lattice of WeylSCs result in different optical responses, which are manifested as characteristic magneto-optical conductivity curves. We also show that, compared to the topologically protected, charge-neutral, localized Majorana zero mode (MZM), the chiral symmetry-protected ZLL is non-charge-neutral and delocalized. Both of these zero modes may be observed in the mixed state of a heterostructure topological superconductor.

cond-mat.supr-con↗

arXiv2025

Three-family supersymmetric Pati-Salam models from intersecting D6-branes on rigid cycles

Intersecting D6-brane models without discrete torsion typically suffer from unstabilized open string moduli, arising from D-brane positions and Wilson lines. These moduli generate additional massless adjoint fields, obstructing the realization of negative beta functions necessary for asymptotic freedom unless they are decoupled around string scale. A viable solution involves utilizing rigid cycles, which eliminate these unwanted adjoint fields. In this work, we for the first time present a class of consistent three-family supersymmetric Pati-Salam models from rigid intersecting D6-branes on the factorizable $\mathbb{T}^6/(\mathbb{Z}_2 \times \mathbb{Z}_2^\prime)$ orientifold with discrete torsion. These models satisfy all the known consistency conditions, including $\mathcal{N}=1$ supersymmetry, K-theory constraints, tadpole cancellation, and recent swampland bounds on the maximal gauge group rank. We provide detailed particle spectra, analyze their phenomenological implications, and discuss the decoupling of exotic states through strong dynamics in the hidden sector.

hep-th↗

arXiv2025

Three family supersymmetric Pati-Salam model from rigid intersecting D6-branes

We construct, for the first time, a three-family $\mathcal{N}=1$ supersymmetric Pati-Salam model from rigid intersecting D6-branes on a factorizable $\mathbb{T}^6/(\mathbb{Z}_2\times \mathbb{Z}_2')$ orientifold with discrete torsion. The factorizable geometry allows for explicit control over rigid cycles and moduli stabilization. We can break the Pati-Salam gauge symmetry down to the Standard Model (SM) gauge symmetry via the supersymmetry preserving Higgs mechanism, generate the SM fermion masses and mixings, and break the supersymmetry via gaugino condensations in the hidden sector.

hep-th↗

arXiv2025

Efficient Multi-Task Learning via Generalist Recommender

Multi-task learning (MTL) is a common machine learning technique that allows the model to share information across different tasks and improve the accuracy of recommendations for all of them. Many existing MTL implementations suffer from scalability issues as the training and inference performance can degrade with the increasing number of tasks, which can limit production use case scenarios for MTL-based recommender systems. Inspired by the recent advances of large language models, we developed an end-to-end efficient and scalable Generalist Recommender (GRec). GRec takes comprehensive data signals by utilizing NLP heads, parallel Transformers, as well as a wide and deep structure to process multi-modal inputs. These inputs are then combined and fed through a newly proposed task-sentence level routing mechanism to scale the model capabilities on multiple tasks without compromising performance. Offline evaluations and online experiments show that GRec significantly outperforms our previous recommender solutions. GRec has been successfully deployed on one of the largest telecom websites and apps, effectively managing high volumes of online traffic every day.

cs.IR↗

arXiv2025

Landau levels in the mixed state of two-dimensional nodal superconductors: models, featured magneto-optical response and quantized thermal Hall effect

Landau quantization of low-energy quasiparticles (QPs) in the mixed state of gapless superconductors is a celebrated problem. So far, the only superconducting system that has been shown to host Landau levels (LLs) of Bogoliubov QPs is the Weyl superconductor. Here, we first investigate the QPs in the mixed state of two Weyl superconductors, an intrinsic one and a heterostructure one, and reveal that the QP states in the former do not form LLs, in contrast to those in the latter where LLs of QPs are shown to exist. The key is whether the low-energy Hamiltonian respects a generalized chiral symmetry. Following the analysis, we show that a twodimensional superconducting system -- a topological insulator-superconductor heterostructure respecting the generalized chiral symmetry -- exhibits LLs with Chern number $\pm 1$ in the mixed state. We also show featured responses resulting from the LLs, including peaked magneto-optical conductivity and quantized thermal Hall conductivity, which could be used as experimental probes to detect LLs in superconductors.

cond-mat.supr-con↗

arXiv2024

Landau levels and optical conductivity in the mixed state of a generic Weyl superconductor

The low-energy quasiparticle states in the mixed state of most superconductors remain Bloch waves due to the presence of supercurrent around vortex cores. In contrast, the Weyl superconductor (WSC) may display Dirac-Landau levels in the presence of a vortex lattice. Here, we investigate the Landau level (LL) structure and optical conductivity in the mixed state of a generic WSC using a heterostructure model, where the tilt of the Bogoliubov-Weyl (BW) cones can be tuned, yielding either type-I (undertilted) or type-II (overtilted) cones. We find that, in a magnetic field, the tilted type-I BW cone in the mixed state may exhibit squeezed LLs with reduced spacings. On the other hand, the spectrum of type-II cones shows a dependence on the angle between the magnetic field and the tilt direction; LL quantization is only possible if the angle is below a critical value. For zero tilt, the optical conductivity in the mixed state of the WSC shows peaks only at photon frequencies $ω_n \propto \sqrt{n}+\sqrt{n+1}$, with a linear background. However, the tilt of BW cones results in the emergence of optical transitions beyond the usual dipolar ones. For type-II BW cones, unique intraband transition conductivity peaks emerge at low frequency, which can serve as an indicator to distinguish between type-I and type-II BW cones in WSCs.

cond-mat.supr-con↗

arXiv2024

MIPI 2024 Challenge on Nighttime Flare Removal: Methods and Results

The increasing demand for computational photography and imaging on mobile platforms has led to the widespread development and integration of advanced image sensors with novel algorithms in camera systems. However, the scarcity of high-quality data for research and the rare opportunity for in-depth exchange of views from industry and academia constrain the development of mobile intelligent photography and imaging (MIPI). Building on the achievements of the previous MIPI Workshops held at ECCV 2022 and CVPR 2023, we introduce our third MIPI challenge including three tracks focusing on novel image sensors and imaging algorithms. In this paper, we summarize and review the Nighttime Flare Removal track on MIPI 2024. In total, 170 participants were successfully registered, and 14 teams submitted results in the final testing phase. The developed solutions in this challenge achieved state-of-the-art performance on Nighttime Flare Removal. More details of this challenge and the link to the dataset can be found at https://mipi-challenge.org/MIPI2024/.

cs.CV↗

arXiv2024

Superconducting Klein and anti-Klein tunneling in Weyl junctions

Klein tunneling is an old topic in relativistic quantum physics, and has been observed recently in graphene where massless particles reside. Here, we propose a new heterostructure platform for Klein tunneling to occur, which consists of a Weyl-semimetal-based normal state/superconductor (NS) junction. By developing a Blonder-Tinkham-Klapwijk-like theory, we find that Klein tunneling occurs at normal incidence, which can lead to differential conductance doubling. If the (single) Weyl semimeltals are replaced by double Weyl semimetals, anti-Klein tunneling will take place of Klein tunneling. Our work provides a theoretical guide for the detection of (anti-)Klein tunneling in three-dimensional chiral NS junctions.

cond-mat.mes-hall↗

arXiv2023

Classification of spin Hall effect in two-dimensional systems

Physical properties such as the conductivity are usually classified according to the symmetry of the underlying system using Neumann's principle, which gives an upper bound for the number of independent components of the corresponding property tensor. However, for a given Hamiltonian, this global approach usually can not give a definite answer on whether a physical effect such as spin Hall effect (SHE) exists or not. It is found that the parity and types of spin-orbit interactions (SOIs) are good indicators that can further reduce the number of independent components of the spin Hall conductivity for a specific system. In terms of the parity as well as various Rashba-like and Dresselhaus-like SOIs, we propose a local approach to classify SHE in two-dimensional (2D) two-band models, where sufficient conditions for identifying the existence or absence of SHE in all 2D magnetic point groups are presented.

cond-mat.mes-hall↗

arXiv2023

Unconventional transport properties in systems with triply degenerate quadratic band crossings

A quadratic band crossing (QBC) is a crossing of two bands with quadratic dispersion, which has been intensively investigated due to its appearance in Bernal-stacked bilayer graphene. Here, we study an extension of QBCs, the triply degenerate quadratic band crossing (TQBC), which is a three-band crossing node containing two quadratic dispersing bands and a flat band. We focus on two types of TQBCs. The first type contains a symmetry-protected QBC and a free-electron band, the prototype of which is the AA-stacked bilayer squareoctagon lattice. In a magnetic field, such a TQBC exhibits an anomalous Landau level structure, leading to a distinctive quantum Hall effect which displays an infinite ladder of Hall plateaus when the chemical potential approaches zero. The other type of TQBC can be viewed as a pseudospin-1 extension of the bilayer-graphene QBC. Under perturbations, this type of TQBCs may split into linear pseudospin-1 Dirac-Weyl fermions. When tunneling through a potential barrier, the transmission probability of the first type decays exponentially with the barrier width for any incident angle, similar to the free-electron case, while the second type hosts an all-angle perfect reflection when the energy of the incident particles is equal to half the barrier height.

cond-mat.mes-hall↗

arXiv2023

Third-order intrinsic anomalous Hall effect with generalized semiclassical theory

The linear intrinsic anomalous Hall effect (IAHE) and second-order IAHE have been intensively investigated in time-reversal broken systems. However, as one of the important members of the nonlinear Hall family, the investigation of third-order IAHE remains absent due to the lack of an appropriate theoretical approach, although the third-order extrinsic AHE has been studied within the framework of first- and second-order semiclassical theory. Herein, we generalize the semiclassical theory for Bloch electrons under the uniform electric field up to the third-order using wavepacket method and based on which we predict that the third-order IAHE can also occur in time-reversal broken systems. Same as the second-order IAHE, we find the band geometric quantity, the second-order field-dependent Berry curvature arising from the second-order field-induced positional shift, plays a pivotal role to observe this effect. Moreover, with symmetry analysis, we find that the third-order IAHE, as the leading contribution, is supported by 15 time-reversal broken 3D magnetic point groups (MPGs), corresponding to a wide class of antiferromagnetic (AFM) materials. Guided by the symmetry arguments, a two-band model is chosen to demonstrate the generalized theory. Furthermore, the generalized third-order semiclassical theory depends only on the properties of Bloch bands, implying that it can also be employed to explore the IAHE in realistic AFM materials, by combining with first-principles calculations.

cond-mat.mes-hall↗

arXiv2023

Quantum Fluctuation of the Quantum Geometric Tensor and its Manifestation as Intrinsic Hall Signatures in Time-Reversal Invariant Systems

In time-reversal invariant systems, all charge Hall effects predicted so far are extrinsic effects due to the dependence on the relaxation time. We explore intrinsic Hall signatures by studying quantum noise spectrum of the Hall current in time-reversal invariant systems, and discover intrinsic thermal Hall noises in both linear and nonlinear regimes. As the band geometric characteristics, quantum geometric tensor and Berry curvature play critical roles in various Hall effects, so are their quantum fluctuations. It is found that the thermal Hall noise in linear order of the electric field is purely intrinsic, and the second-order thermal Hall noise has both intrinsic and extrinsic contributions. In particular, the intrinsic part of the second-order thermal Hall noise is a manifestation of the quantum fluctuation of quantum geometric tensor, which widely exists as long as Berry curvature is nonzero. These intrinsic thermal Hall noises provide direct measurable means to band geometric information, including Berry curvature related quantities and quantum fluctuation of quantum geometric tensor.

cond-mat.mes-hall↗

arXiv2022

A semiclassical approach to surface Fermi arcs in Weyl semimetals

We present a semiclassical explanation for the morphology of the surface Fermi arcs of Weyl semimetals. Viewing the surface states as a two-dimensional Fermi gas subject to band bending and Berry curvatures, we show that it is the non-parallelism between the velocity and the momentum that gives rise to the spiral structure of Fermi arcs. We map out the Fermi arcs from the velocity field for a single Weyl point and a lattice with two Weyl points. We also investigate the surface magnetoplasma of Dirac semimetals in a magnetic field, and find that the drift motion, the chiral magnetic effect and the Imbert-Fedorov shift are all involved in the formation of surface Fermi arcs. Our work not only provides an insightful perspective on the surface Fermi arcs and a practical way to find the surface dispersion, but also paves the way for the study of other physical properties of the surface states of topological semimetals, such as transport properties and orbital magnetization, using semiclassical methods.

cond-mat.mes-hall↗

arXiv2022

Quantum third-order nonlinear Hall effect of a four-terminal device with time-reversal symmetry

The third-order nonlinear Hall effect induced by Berry-connection polarizability tensor has been observed in Weyl semimetals T$_d$-MoTe$_2$ as well as T$_d$-TaIrTe$_4$. The experiments were performed on bulk samples, and the results were interpreted with the semiclassical Boltzmann approach. Beyond the bulk limit, we develop a quantum nonlinear transport theory to investigate the third-order Hall response of a four-terminal setup with time-reversal symmetry in quantum regime. The quantum nonlinear theory is verified on a model system of monolayer MoTe$_2$, and numerical results on the angle-resolved Hall currents are qualitatively consistent with the experiment. More importantly, quantum signatures of the third-order Hall effect are revealed, which are independent of the system symmetry. The first quantum signature is quantum enhancement of the third-order Hall current, which is characterized by sharp current peaks whose magnitudes are three orders larger than the first-order Hall current. Such quantum enhancement originates from quantum interference in coherent transport, and it can be easily destroyed by dephasing effect. The second quantum signature is disorder-induced enhancement of the third-order Hall current for weak disorders. Our findings reveal quantum characteristics of the third-order Hall effect, and we propose feasible ways to enhance it in nanoscale systems. The quantum third-order theory developed in this work provides a general formalism for describing nonlinear coherent transport properties in multi-terminal devices, regardless of the system symmetry.

cond-mat.mes-hall↗

arXiv2021

Triply degenerate nodal lines in topological and non-topological metals

Topological nodal-line semimetals exhibit double or fourfold degenerate nodal lines, which are protected by symmetries. Here, we investigate the possibility of the existence of triply degenerate nodal lines in metals. We present two types of triply degenerate nodal lines, one topologically trivial and the other nontrivial. The first type is stacked by two-dimensional pseudospin-1 fermions, which can be viewed as an critical case of a tunable band-crossing line structure that contains a symmetry-protected quadratic band-crossing line and a non-degenerate band, and can split into four Weyl nodal lines under perturbations. We find that surface states of the nodal line structure are dependent on the geometry of the lattice and the surface termination. Such a metal has a nesting of Fermi surface in a range of filling, resulting in a density-wave state when interaction is included. The second type is a vortex ring of pseudospin-1 fermions. In this system, the pseudospins form Skyrmion textures, and the surface states are fully extended topological Fermi arcs so that the model exhibits 3D quantum anomalous Hall effect with a maximal Hall conductivity. The vortex ring can evolve into a pair of vortex lines that are not closed in the first Brillouin zone. A vortex line cannot singly exist in the lattice model if it is the only nodal feature of the system.

cond-mat.mtrl-sci↗

arXiv2020

Context-Aware Drive-thru Recommendation Service at Fast Food Restaurants

Drive-thru is a popular sales channel in the fast food industry where consumers can make food purchases without leaving their cars. Drive-thru recommendation systems allow restaurants to display food recommendations on the digital menu board as guests are making their orders. Popular recommendation models in eCommerce scenarios rely on user attributes (such as user profiles or purchase history) to generate recommendations, while such information is hard to obtain in the drive-thru use case. Thus, in this paper, we propose a new recommendation model Transformer Cross Transformer (TxT), which exploits the guest order behavior and contextual features (such as location, time, and weather) using Transformer encoders for drive-thru recommendations. Empirical results show that our TxT model achieves superior results in Burger King's drive-thru production environment compared with existing recommendation solutions. In addition, we implement a unified system to run end-to-end big data analytics and deep learning workloads on the same cluster. We find that in practice, maintaining a single big data cluster for the entire pipeline is more efficient and cost-saving. Our recommendation system is not only beneficial for drive-thru scenarios, and it can also be generalized to other customer interaction channels.

cs.IR↗