arXiv subjects

Xuan Luo

Publications and source records attributed to Xuan Luo.

At least 109 records · Page 6Linked to original sources

arXiv2022

Reconcile the Bulk Metallic and Surface Insulating state in 1T-TaSe$_2$

The transition metal dichalcogenides 1T-TaS$_2$ and 1T-TaSe$_2$ have been extensively studied for the complicated correlated electronic properties. The origin of different surface electronic states remains controversial. We apply scanning tunneling microscopy and spectroscopy to restudy the surface electronic state of bulk 1T-TaSe$_2$. Both insulating and metallic states are identified in different areas of the same sample. The insulating state is similar to that in 1T-TaS$_2$, concerning both the dI/dV spectrum and the orbital texture. With further investigations in single-step areas, the discrepancy of electronic states is found to be associated with different stacking orders. The insulating state is most possibly a single-layer property, modulated to a metallic state in some particular stacking orders. Both the metallic and large-gap insulating spectra, together with their corresponding stacking orders, are dominant in 1T-TaSe$_2$. The connected metallic areas lead to the metallic transport behavior. We then reconcile the bulk metallic and surface insulating state in 1T-TaSe$_2$. The rich phenomena in 1T-TaSe$_2$ deepen our understanding of the correlated electronic state in bulk 1T-TaSe$_2$ and 1T-TaS$_2$.

cond-mat.str-el↗

arXiv2022

Consistent Style Transfer

Recently, attentional arbitrary style transfer methods have been proposed to achieve fine-grained results, which manipulates the point-wise similarity between content and style features for stylization. However, the attention mechanism based on feature points ignores the feature multi-manifold distribution, where each feature manifold corresponds to a semantic region in the image. Consequently, a uniform content semantic region is rendered by highly different patterns from various style semantic regions, producing inconsistent stylization results with visual artifacts. We proposed the progressive attentional manifold alignment (PAMA) to alleviate this problem, which repeatedly applies attention operations and space-aware interpolations. The attention operation rearranges style features dynamically according to the spatial distribution of content features. This makes the content and style manifolds correspond on the feature map. Then the space-aware interpolation adaptively interpolates between the corresponding content and style manifolds to increase their similarity. By gradually aligning the content manifolds to style manifolds, the proposed PAMA achieves state-of-the-art performance while avoiding the inconsistency of semantic regions. Codes are available at https://github.com/computer-vision2022/PAMA.

cs.CV↗

arXiv2022

First Principles Investigation of Transition Metal Doped WSe$_{2}$ Monolayer for Photocatalytic Water Splitting

Photocatalytic water splitting is a promising renewable energy source as an alternative for limited fossil fuels. The effectiveness of the conversion from solar energy to hydrogen fuel relies primarily on the material. Previously, researchers studied different TMDs such as WS$_{2}$, and PdSe$_{2}$. These materials perform well in certain aspects such as strong adsorption stability and promising abilities for HER, however, their band gaps are still not ideal. In this paper, we studied a new TMD material WSe$_{2}$, which is currently used in heterostructure photocatalysts. To our knowledge, this is the first assessment of using transition metal doped WSe$_{2}$ as potential photocatalysts for photocatalytic water splitting. Using first principles calculations, we evaluated the band gaps and other photocatalytic abilities of pristine WSe2 as well as Cr, Mo, Ta, and Re doped WSe$_{2}$. Compared to previously studied TMD materials, three of our newly studied materials (pristine, Mo doped, and Ta doped WSe$_{2}$)demonstrated more desirable band gaps, which are closer to being ideal (1.23eV); The band edge positions of our materials are also closer to the ideal reduction potential of H$^{+}$/H$_{2}$ and the oxidation potential of O$_{2}$/H$_{2}$O. Furthermore, Mo and Ta doped WSe$_{2}$ monolayers undergo an exothermic process, indicating stable monolayers. Of the three selected materials, pristine WSe$_{2}$ exhibits the strongest water adsorption abilities. Our results substantiates pristine, Mo doped, and Cr doped WSe$_{2}$ as potential photocatalysts for water splitting.

cond-mat.mtrl-sci↗

arXiv2021

Observation and manipulation of a phase separated state in a charge density wave material

The 1T polytype of TaS$_\textrm{2}$ has been studied extensively as a strongly correlated system. As 1T-TaS$_\textrm{2}$ is thinned towards the 2D limit, its phase diagram shows significant deviations from that of the bulk material. Optoelectronic maps of ultrathin 1T-TaS$_\textrm{2}$ have indicated the presence of non-equilibrium charge density wave phases within the hysteresis region of the nearly commensurate (NC) to commensurate (C) transition. We perform scanning tunneling microscopy on exfoliated ultrathin flakes of 1T-TaS$_\textrm{2}$ within the NC-C hysteresis window, finding evidence that the observed non-equilibrium phases consist of intertwined, irregularly shaped NC-like and C-like domains. After applying lateral electrical signals to the sample we image changes in the geometric arrangement of the different regions. We use a phase separation model to explore the relationship between electronic inhomogeneity present in ultrathin 1T-TaS$_\textrm{2}$ and its bulk resistivity. These results demonstrate the role of phase competition morphologies in determining the properties of 2D materials.

cond-mat.mes-hall↗

arXiv2021

Time-Travel Rephotography

Many historical people were only ever captured by old, faded, black and white photos, that are distorted due to the limitations of early cameras and the passage of time. This paper simulates traveling back in time with a modern camera to rephotograph famous subjects. Unlike conventional image restoration filters which apply independent operations like denoising, colorization, and superresolution, we leverage the StyleGAN2 framework to project old photos into the space of modern high-resolution photos, achieving all of these effects in a unified framework. A unique challenge with this approach is retaining the identity and pose of the subject in the original photo, while discarding the many artifacts frequently seen in low-quality antique photos. Our comparisons to current state-of-the-art restoration filters show significant improvements and compelling results for a variety of important historical people.

cs.CV↗

arXiv2021

Li-doped Beryllonitrene for Enhanced Carbon Dioxide Capture

In recent years, the scientific community has given more and more attention to the issue of climate change and global warming, which is largely attributed to the massive quantity of carbon dioxide emissions. Thus, the demand for a carbon dioxide capture material is massive and continuously increasing. In this study, we perform first-principle calculations based on density functional theory to investigate the carbon dioxide capture ability of pristine and doped beryllonitrene. Our results show that carbon dioxide had an adsorption energy of -0.046 eV on pristine beryllonitrene, so it appears that beryllonitrene has extremely weak carbon dioxide adsorption ability. Pristine beryllonitrene could be effectively doped with Lithium atoms, and the resulting Li-doped beryllonitrene had much stronger interactions with carbon dioxide than pristine beryllonitrene. The adsorption energy for carbon dioxide on Li-doped beryllonitrene was -0.408 eV. The adsorption of carbon dioxide on Li-doped beryllonitrene greatly changed the charge density, projected density of states, and band structure of the material, demonstrating that it was strongly adsorbed. This suggests that Li-doping is a viable way to enhance the carbon dioxide capture ability of beryllonitrene and makes it a possible candidate for an effective CO$_2$ capture material.

cond-mat.mtrl-sci↗

arXiv2021

Tuning the Magnetic and Electronic Properties of Monolayer VI3 by 3d Transition Metal Doping: A First-Principles Study

Two-dimensional (2D) materials with robust magnetism have drawn immense attention for their promising applications in spintronics. Recently, intrinsic ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To enhance its spintronic property, we modified VI3 by interstitial doping with 3d transition metals (TM) and used first-principles calculations to investigate the geometric structure, formation energy, electronic property, and magnetism of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal (Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 materials, four of them (Ti-, V-, Mn-, and Ni-doped VI3) show robust magnetism with full spin polarization near the Fermi energy. Our research demonstrates that Ti-doped VI3 results in half-metallic semiconductor properties (HMS), while V-doped VI3 and Ni-doped VI3 result in half-semiconductor properties (HSC). Surprisingly, Mn-doped VI3 exhibits an unusual bipolar magnetic semiconductor property (BMS). This unique combination of strong ferromagnetism and 100% spin polarization with a half-metallic, half-semiconductor, or bipolar semiconductor property renders 3d TM-doped VI3 as potential candidates for next generation semiconductor spintronic applications. These spin-polarized materials will be extremely useful for spin-current generation and other spintronic applications.

cond-mat.mtrl-sci↗

arXiv2021

Triangle mechanism in the decay process $J/ψ\to K^- K^+ a_1(1260)$

The role of triangle mechanism in the decay process $J/ψ\to K^- K^+ a_1(1260)$ is probed. In this mechanism, a close-up resonance with mass $1823$ MeV and width $122$ MeV decays into $K^* ϕ, K^* \to K π$ and then $K^* \bar{K}$ fuses into the $a_1(1260)$ resonance. We find that this mechanism leads to a triangle singularity around $M_{\rm inv}(K^- a_1(1260))\approx 1920$ MeV, where the axial-vector meson $a_1(1260)$ is considered as a dynamically generated resonance. With the help of the triangle mechanism we find sizable branching ratios $\text{Br}(J/ψ\to K^- K^+ a_1(1260),a_1 \to πρ)=1.210 \times 10^{-5}$ and $\text{Br}(J/ψ\to K^- K^+ a_1(1260))=3.501 \times 10^{-5}$. Such a effect from triangle mechanism of the decay process could be investigated by such as BESIII, LHCb and Belle-II experiments. This potential investigation can help us obtain the information of the axial-vector meson $a_1(1260)$.

hep-ph↗

arXiv2021

Data Pricing in Machine Learning Pipelines

Machine learning is disruptive. At the same time, machine learning can only succeed by collaboration among many parties in multiple steps naturally as pipelines in an eco-system, such as collecting data for possible machine learning applications, collaboratively training models by multiple parties and delivering machine learning services to end users. Data is critical and penetrating in the whole machine learning pipelines. As machine learning pipelines involve many parties and, in order to be successful, have to form a constructive and dynamic eco-system, marketplaces and data pricing are fundamental in connecting and facilitating those many parties. In this article, we survey the principles and the latest research development of data pricing in machine learning pipelines. We start with a brief review of data marketplaces and pricing desiderata. Then, we focus on pricing in three important steps in machine learning pipelines. To understand pricing in the step of training data collection, we review pricing raw data sets and data labels. We also investigate pricing in the step of collaborative training of machine learning models, and overview pricing machine learning models for end users in the step of machine learning deployment. We also discuss a series of possible future directions.

cs.LG↗

arXiv2021

Phonon-related monochromatic THz radiation and its magneto-modulation in 2D ferromagnetic Cr2Ge2Te6

Searching multiple types of terahertz (THz) irradiation source is crucial for the THz technology. Here, by utilizing a two-dimensional (2D) ferromagnetic Cr2Ge2Te6 crystal, we firstly demonstrate a magneto-tunable monochromatic THz irradiation source. With a low-photonic-energy broadband THz pump, a strong THz irradiation with frequency ~0.9 THz and bandwidth ~0.25 THz can be generated and its conversion efficiency could even reach 2.1% at 160 K. Moreover, it is intriguing to find that such monochromatic THz irradiation can be efficiently modulated by the magnetic field below 160 K. According to both experimental and theoretical analyses, the emergent THz irradiation is identified as the emission from the phonon-polariton and its temperature and magnetic field dependent behaviors confirmed the large spin-lattice coupling in this 2D ferromagnetic crystal. These observations provide a new route for the creation of tunable monochromatic THz source which may have great practical interests in future applications in photonic and spintronic devices.

physics.optics↗

arXiv2021

Theoretical study in the $\bar{B}^0 \to J/ψ\bar{K}^{*0} K^0$ and $\bar{B}^0 \to J/ψf_1(1285)$ decays

We study the decay processes of $\bar{B}^0 \to J/ψ\bar{K}^{*0} K^0$ and $\bar{B}^0 \to J/ψf_1(1285)$ to analyse the $f_1(1285)$ resonance. By the calculation within chiral unitary approach where $f_1(1285)$ resonance is dynamically generated from the $K^*\bar{K}-c.c.$ interaction, we find that the $\bar{K}^{*0} K^0$ invariant mass distribution has a clear broad peak. Such broad peak has been understood as the signal of the $f_1(1285)$. Finally, we obtain a theoretical result $R_t=Γ_{\bar{B}^0 \to J/ψ\bar{K}^{*0} K^0}/Γ_{\bar{B}^0 \to J/ψf_1(1285)}$ which is expected to be compared with the experimental data.

hep-ph↗

arXiv2021

Giant $c$-axis nonlinear anomalous Hall effect in T$_d$-MoTe$_2$ and WTe$_2$

While the anomalous Hall effect can manifest even without an external magnetic field, time reversal symmetry is nonetheless still broken by the internal magnetization of the sample. Recently, it has been shown that certain materials without an inversion center allow for a nonlinear type of anomalous Hall effect whilst retaining time reversal symmetry. The effect may arise from either Berry curvature or through various asymmetric scattering mechanisms. Here, we report the observation of an extremely large $c$-axis nonlinear anomalous Hall effect in the non-centrosymmetric T$_d$ phase of MoTe$_2$ and WTe$_2$ without intrinsic magnetic order. We find that the effect is dominated by skew-scattering at higher temperatures combined with another scattering process active at low temperatures. Application of higher bias yields an extremely large Hall ratio of $E_\perp /E_\parallel$=2.47 and corresponding anomalous Hall conductivity of order 8x10$^7$S/m.

cond-mat.mes-hall↗

arXiv2021

RL-CSDia: Representation Learning of Computer Science Diagrams

Recent studies on computer vision mainly focus on natural images that express real-world scenes. They achieve outstanding performance on diverse tasks such as visual question answering. Diagram is a special form of visual expression that frequently appears in the education field and is of great significance for learners to understand multimodal knowledge. Current research on diagrams preliminarily focuses on natural disciplines such as Biology and Geography, whose expressions are still similar to natural images. Another type of diagrams such as from Computer Science is composed of graphics containing complex topologies and relations, and research on this type of diagrams is still blank. The main challenges of graphic diagrams understanding are the rarity of data and the confusion of semantics, which are mainly reflected in the diversity of expressions. In this paper, we construct a novel dataset of graphic diagrams named Computer Science Diagrams (CSDia). It contains more than 1,200 diagrams and exhaustive annotations of objects and relations. Considering the visual noises caused by the various expressions in diagrams, we introduce the topology of diagrams to parse topological structure. After that, we propose Diagram Parsing Net (DPN) to represent the diagram from three branches: topology, visual feature, and text, and apply the model to the diagram classification task to evaluate the ability of diagrams understanding. The results show the effectiveness of the proposed DPN on diagrams understanding.

cs.CV↗

arXiv2021

Kotzinian-Mulders effect in semi-inclusive DIS within TMD factorization

In this paper we study the Kotzinian-Mulders effect of a single hadron production in semi-inclusive deep inelastic scattering (SIDIS) within the framework of transverse momentum dependent (TMD) factorization. The asymmetry is contributed by the convolution of the Kotzinian-Mulders function $g_{1T}$ and the unpolarized fragmentation function $D_1$. As a TMD distribution, the Kotzinian-Mulders function in the coordinate space in the perturbative region can be represented as the convolution of the $C$-coefficients and the corresponding collinear correlation function. The Wandzura-Wilczek approximation is used to obtain this correlation function. We perform a detailed phenomenological numerical analysis of the Kotzinian-Mulders effect in the SIDIS process within TMD factorization at the kinematics of the HERMES and COMPASS measurements. It is found that the obtained $x_B$-, $z_h$- and $P_{h\perp}$-dependent Kotzinian-Mulders effect are basically consistent with the HERMES and COMPASS measurements.

hep-ph↗

arXiv2020

Photocurrent Imaging of Multi-Memristive Charge Density Wave Switching in Two-Dimensional 1T-TaS2

Transport studies of atomically thin 1T-TaS2 have demonstrated the presence of intermediate resistance states across the nearly commensurate (NC) to commensurate (C) charge density wave (CDW) transition, which can be further switched electrically. While this presents exciting opportunities for the material in memristor applications, the switching mechanism has remained elusive and could be potentially attributed to the formation of inhomogeneous C and NC domains across the 1T-TaS2 flake. Here, we present simultaneous electrical driving and scanning photocurrent imaging of CDWs in ultrathin 1T-TaS2 using a vertical heterostructure geometry. While micron-sized CDW domains form upon changing temperature, electrically driven transitions result in largely uniform changes, indicating that states of intermediate resistance for the latter likely correspond to true metastable CDW states in between the NC and C phases, which we then explain by a free energy analysis. Additionally, we are able to perform repeatable and bidirectional switching across the multiple CDW states without changing sample temperature, demonstrating that atomically thin 1T-TaS2 can be further used as a robust and reversible multi-memristor material.

cond-mat.mtrl-sci↗

arXiv2020

Consistent Video Depth Estimation

We present an algorithm for reconstructing dense, geometrically consistent depth for all pixels in a monocular video. We leverage a conventional structure-from-motion reconstruction to establish geometric constraints on pixels in the video. Unlike the ad-hoc priors in classical reconstruction, we use a learning-based prior, i.e., a convolutional neural network trained for single-image depth estimation. At test time, we fine-tune this network to satisfy the geometric constraints of a particular input video, while retaining its ability to synthesize plausible depth details in parts of the video that are less constrained. We show through quantitative validation that our method achieves higher accuracy and a higher degree of geometric consistency than previous monocular reconstruction methods. Visually, our results appear more stable. Our algorithm is able to handle challenging hand-held captured input videos with a moderate degree of dynamic motion. The improved quality of the reconstruction enables several applications, such as scene reconstruction and advanced video-based visual effects.

cs.CV↗

arXiv2020

Possible strain induced Mott gap collapse in 1T-TaS$_2$

Tuning the electronic properties of a matter is of fundamental interest in scientific research as well as in applications. Recently, the Mott insulator-metal transition has been reported in a pristine layered transition metal dichalcogenides 1T-TaS$_2$, with the transition triggered by an optical excitation, a gate controlled intercalation, or a voltage pulse. However, the sudden insulator-metal transition hinders an exploration of how the transition evolves. Here, we report the strain as a possible new tuning parameter to induce Mott gap collapse in 1T-TaS$_2$. In a strain-rich area, we find a mosaic state with distinct electronic density of states within different domains. In a corrugated surface, we further observe and analyze a smooth evolution from a Mott gap state to a metallic state. Our results shed new lights on the understanding of the insulator-metal transition and promote a controllable strain engineering on the design of switching devices in the future.

cond-mat.str-el↗

arXiv2020

T-odd generalized and quasi transverse momentum dependent parton distribution in a scalar spectator model

Generalized transverse momentum dependent parton distributions (GTMDs), as mother funtions of transverse momentum dependent parton distributions (TMDs) and generalized parton distributions (GPDs), encode the most general parton structure of hadrons. We calculate four twist-two time reversal odd GTMDs of pion in a scalar spectator model. We study the dependence of GTMDs on the longitudinal momentum fraction $x$ carried by the active quark and the transverse momentum $|\vec k_T|$ for different values of skewness $ξ$ defined as the longitudinal momentum transferred to the proton as well as the total momentum $|\vecΔ_T|$ transferred to the proton. In addition, the quasi-TMDs and quasi-GPDs of pion have also been investigated in this paper.

hep-ph↗