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Researcher profile

Xuan Luo

Xuan Luo contributes to research discovery and scholarly infrastructure.

ResearcherAffiliation not importedOpen to collaborate
cond-mat.mtrl-scihep-phComputer Visioncond-mat.str-elcond-mat.mes-hallphysics.opticsArtificial IntelligenceComputation and LanguageDatabasesGraphicshep-exHuman-Computer InteractionMachine Learningnucl-thphysics.app-ph

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Published work

28 published item(s)

preprint2026arXiv

AEQ-Bench: Measuring Empathy of Omni-Modal Large Models

While the automatic evaluation of omni-modal large models (OLMs) is essential, assessing empathy remains a significant challenge due to its inherent affectivity. To investigate this challenge, we introduce AEQ-Bench (Audio Empathy Quotient Benchmark), a novel benchmark to systematically assess two core empathetic capabilities of OLMs: (i) generating empathetic responses by comprehending affective cues from multi-modal inputs (audio + text), and (ii) judging the empathy of audio responses without relying on text transcription. Compared to existing benchmarks, AEQ-Bench incorporates two novel settings that vary in context specificity and speech tone. Comprehensive assessment across linguistic and paralinguistic metrics reveals that (1) OLMs trained with audio output capabilities generally outperformed models with text-only outputs, and (2) while OLMs align with human judgments for coarse-grained quality assessment, they remain unreliable for evaluating fine-grained paralinguistic expressiveness.

0 citations0 reviewsNo code linkedOpen access
preprint2026arXiv

WorldReasonBench: Human-Aligned Stress Testing of Video Generators as Future World-State Predictors

Commercial video generation systems such as Seedance2.0 and Veo3.1 have rapidly improved, strengthening the view that video generators may be evolving into "world simulators." Yet the community still lacks a benchmark that directly tests whether a model can reason about how an observed world should evolve over time. We introduce WorldReasonBench, which reframes video generation evaluation as world-state prediction: given an initial state and an action, can a model generate a future video whose state evolution remains physically, socially, logically, and informationally consistent? WorldReasonBench contains 436 curated test cases with structured ground-truth QA annotations spanning four reasoning dimensions and 22 subcategories. We evaluate generated videos with a human-aligned two-part methodology: Process-aware Reasoning Verification uses structured QA and reasoning-phase diagnostics to detect temporal and causal failures, while Multi-dimensional Quality Assessment scores reasoning quality, temporal consistency, and visual aesthetics for ranking and reward modeling. We further introduce WorldRewardBench, a preference benchmark with approximately 6K expert-annotated pairs over 1.4K videos, supporting pair-wise and point-wise reward-model evaluation. Across modern video generators, our results expose a persistent gap between visual plausibility and world reasoning: videos can look convincing while failing dynamics, causality, or information preservation. We will release our benchmarks and evaluation toolkit to support community research on genuinely world-aware video generation at https://github.com/UniX-AI-Lab/WorldReasonBench/.

0 citations0 reviewsNo code linkedOpen access
preprint2024arXiv

Theoretical study of the $B^+\to D^-D_s^{+}π^+$ reaction

Prompted by the recent discoveries of $T_{c\bar{s}0}(2900)^{++}$ in the $D_s^+π^+$ invariant mass distribution of $B^+\to D^-D_s^+π^+$ process, we present a model that hopes to help us investigate the nature of $T_{c\bar{s}0}(2900)^{++}$ by reproducing the mass distribution of $D^-π^+, D_s^+π^+$ and $D^-D_s^+$ in $B^+ \to D^-D_s^+π^+$ decays. The structure of the triangular singularity peak generated from the $χ_{c1}D^{*+}K^{*+}$ loop near the $D^{*+}K^{*+}$ threshold is considered in our model may be the experimentally discovered resonance-like state structure $T_{c\bar{s}0}(2900)^{++}$. In addition, we employ a coupled-channel approach to describe the dominant contribution of the $Dπ$ $S\text{-wave}$ amplitude, and also consider other excitations. Our model provides a well fit to the invariant mass distributions of $D^-π^+, D_s^+π^+$ and $D^-D_s^+$ simultaneously.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

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.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Doubly-charmed baryon production in $Z$ boson decay

In this paper, we carry out a detailed study of doubly-charmed baryon production in $Z$ boson decay, on the basis of the nonrelativistic QCD factorization. With the inclusion of the di-quark states $(cc)[^3S_1]_{\bar{\textbf{3}}}$ and $(cc)[^1S_0]_{\textbf{6}}$, the branching ratio of $\mathcal{B}_{Z \to Ξ_{cc}+X}$ is predicted to be of the $10^{-5}$ order, indicating its experimental measurability. By comparing to the $Λ^{+}_{c}$ yield in $Z$ decay, we predict $\mathcal{R}_{Ξ_{cc}^{+}}(=\frac{Γ(Z \to Ξ^{+}_{cc}) \times \mathcal{B}(Ξ^{+}_{cc} \to Λ_c^{+}K^{-}π^{+})}{Γ(Z \to Λ_c^{+})})=(0.85^{+0.10}_{-0.07}) \times 10^{-4}$ and $\mathcal{R}_{Ξ_{cc}^{++}}(=\frac{Γ(Z \to Ξ^{++}_{cc}) \times \mathcal{B}(Ξ^{++}_{cc} \to Λ_c^{+}K^{-}π^{+}π^{+})}{Γ(Z \to Λ_c^{+})})=(1.70^{+0.20}_{-0.14}) \times 10^{-4}$, which are at clear variance with the SELEX measurements but comparable with the values given by the LHCb and Belle collaborations.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Effect of Stacking Order on the Electronic State of 1T-TaS$_2$

New theoretical proposals and experimental findings on transition metal dichalcogenide 1T-TaS$_2$ have revived interests in its possible Mott insulating state. We perform a comprehensive scanning tunneling microscopy and spectroscopy experiment on different single-step areas in pristine 1T-TaS$_2$. After accurately determining the relative displacement of Star-of-David super-lattices in two layers, we find different stacking orders can correspond to the similar large-gap spectrum on the upper terrace. When the measurement is performed away from the step edge, the large gap spectrum can always be maintained. The stacking order seems rarely disturb the large-gap spectrum in the ideal bulk material. We conclude that the large insulating gap is from the single-layer property, which is a correlation-induced Mott gap based on the single-band Hubbard model. Specific stacking orders can perturb the state and induce a small-gap or metallic spectrum for a limited area around the step edge, which we attribute to a surface and edge phenomenon. Our work provides more evidence about the surface electronic state and deepens our understanding of the Mott insulating state in 1T-TaS$_2$.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

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.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

High-Performance Mid-IR to Deep-UV van der Waals Photodetectors Capable of Local Spectroscopy at Room Temperature

The ability to perform broadband optical spectroscopy with sub-diffraction-limit resolution is highly sought-after for a wide range of critical applications. However, sophisticated tip-enhanced techniques are currently required to achieve this goal. We bypass this challenge by demonstrating an extremely broadband photodetector based on a two-dimensional (2D) van der Waals heterostructure that is sensitive to light across over a decade in energy from the mid-infrared (MIR) to deep-ultraviolet (DUV) at room temperature. The devices feature high detectivity (> 10^9 cm Hz^1/2 W^-1) together with high bandwidth (2.1 MHz). The active area can be further miniaturized to submicron dimensions, far below the diffraction limit for the longest detectable wavelength of 4.1 um, enabling such devices for facile measurements of local optical properties on atomic-layer-thickness samples placed in close proximity. This work can lead to the development of low-cost and high-throughput photosensors for hyperspectral imaging at the nanoscale.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Impact of $Z \to η_{c,b}+g+g$ on the inclusive $η_{c,b}$ meson yield in $Z$-boson decay

In this paper, we carry out the next-to-leading-order QCD corrections to $Z \to η_Q+g+g~(Q=c,b)$ (labeled as $gg$) through the color-singlet (CS) state of $Q\bar{Q}[^1S_0^{[1]}]$, with the aim of assessing the impact of this process on $Z$ bosons decaying into inclusive $η_Q$. We find that the QCD corrections to the $gg$ process can notably enhance its leading-order results, especially for the $η_c$ case, which would then greatly increase the existing predictions of $Γ_{Z \to η_Q+X}$ given by the CS-dominant process $Z \to η_{Q}[^1S_0^{[1]}]+Q+\bar{Q}$. Moreover, with these significant QCD corrections, the $gg$ process would exert crucial influence on the CS-predicted $η_Q$ energy distributions. In conclusion, in the CS studies of $Z \to η_Q+X$, besides $Z \to η_{Q}[^1S_0^{[1]}]+Q+\bar{Q}$, $Z \to η_Q[^1S_0^{[1]}]+g+g$ can provide phenomenologically indispensable contributions as well.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Inducing and tuning Kondo screening in a narrow-electronic-band system

Although the single-impurity Kondo physics has already been well understood, the understanding of the Kondo lattice problem where a dense array of local moments couples to the conduction electrons is still far from complete. The ability of creating and tuning the Kondo lattice in non-f-electron systems will be great helpful for further understanding the Kondo lattice behavior. Here we show that the Pb intercalation in the charge-density-wave-driven narrow-electronic-band system 1T-TaS2 induces a transition from the insulating gap to a sharp Kondo resonance in the scanning tunneling microscopy measurements. It results from the Kondo screening of the localized moment in the 13-site Star-of-David clusters of 1T-TaS2, and thus confirms the cluster Mott localization of the unpaired electrons and local moment formation in the 1T-TaS2 layer. As increasing the Pb concentration, the narrow electronic band derived from the localized electrons shifts away from the Fermi level and the Kondo resonance peak is gradually suppressed. Our results pave a way for creating and tuning many-body electronic states in layered narrow-electronic-band materials.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

On Shapley Value in Data Assemblage Under Independent Utility

In many applications, an organization may want to acquire data from many data owners. Data marketplaces allow data owners to produce data assemblage needed by data buyers through coalition. To encourage coalitions to produce data, it is critical to allocate revenue to data owners in a fair manner according to their contributions. Although in literature Shapley fairness and alternatives have been well explored to facilitate revenue allocation in data assemblage, computing exact Shapley value for many data owners and large assembled data sets through coalition remains challenging due to the combinatoric nature of Shapley value. In this paper, we explore the decomposability of utility in data assemblage by formulating the independent utility assumption. We argue that independent utility enjoys many applications. Moreover, we identify interesting properties of independent utility and develop fast computation techniques for exact Shapley value under independent utility. Our experimental results on a series of benchmark data sets show that our new approach not only guarantees the exactness of Shapley value, but also achieves faster computation by orders of magnitudes.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Persistent photogenerated state attained by femtosecond laser irradiation of thin $T_d$-MoTe$_2$

Laser excitation has emerged as a means to expose hidden states of matter and promote phase transitions on demand. Such laser induced transformations are often rendered possible owing to the delivery of spatially and/or temporally manipulated light, carrying energy quanta well above the thermal background. Here, we report time-resolved broadband femtosecond (fs) transient absorption measurements on thin flakes of Weyl semimetal candidate $T_d$-MoTe$_2$ subjected to various levels and schemes of fs-photoexcitation. Our results reveal that impulsive fs-laser irradiation alters the interlayer behavior of the low temperature $T_d$ phase as evidenced by the persistent disappearance of its characteristic coherent $^1$A$_1$ $=$ 13 cm$^{-1}$ shear phonon mode. We found that this structural transformation withstands thermal annealing up to 500 K, although it can be reverted to the 1$T$\' phase by fs-laser treatment at room temperature. Our work opens the door to reversible optical control of topological properties.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Photoinduced Interlayer Dynamics in T$_d$-MoTe$_2$: A Broadband Pump-Probe Study

We report on time-resolved broadband transient reflectivity (tr-bb-TR) measurements performed on a bulk single crystal of T$_d$-MoTe$_2$ as a function of the incident pump fluence (F). Tr-bb-TR data unveil photoinduced electronic changes progressing on the sub-picosecond timescale as well as the dynamics of the coherent low-frequency $^1A_1$ interlayer shear phonon. Our results indicate a gradual evolution of both the TR and the $^1A_1$ Fourier intensity spectra as a function of F, ruling out the threshold-like change that has been associated with the ultrafast photoinduced $T_d \to 1T'$ phase transition. We also observe a large redshift of the $^1A_1$ Fourier spectral features, which suggests that large renormalization effects are taking place on interband transitions that are dielectrically susceptible to the $^1A_1$ interlayer phonon displacement.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

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$_2$.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

StyleSDF: High-Resolution 3D-Consistent Image and Geometry Generation

We introduce a high resolution, 3D-consistent image and shape generation technique which we call StyleSDF. Our method is trained on single-view RGB data only, and stands on the shoulders of StyleGAN2 for image generation, while solving two main challenges in 3D-aware GANs: 1) high-resolution, view-consistent generation of the RGB images, and 2) detailed 3D shape. We achieve this by merging a SDF-based 3D representation with a style-based 2D generator. Our 3D implicit network renders low-resolution feature maps, from which the style-based network generates view-consistent, 1024x1024 images. Notably, our SDF-based 3D modeling defines detailed 3D surfaces, leading to consistent volume rendering. Our method shows higher quality results compared to state of the art in terms of visual and geometric quality.

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

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.

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

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.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

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.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Double spin asymmetry in dihadron production in SIDIS off the longitudinally polarized nucleon target

In this paper we study the double longitudinal spin asymmetry of dihadron production in semi-inclusive deep inelastic scattering (SIDIS). We calculate a unknown twist-3 dihadron fragmentation function $\widetilde{D}^\sphericalangle$ within a spectator model which has been used successfully in describing the dihadron production in both the unpolarized and the single polarized processes. The collinear picture, in which the transverse momentum of the final state hadron pair is integrated out, has been considered. The $\cosϕ_R$ azimuthal asymmetry arises from the coupling $e_L H_1^\sphericalangle$ and the coupling $g_1 \widetilde{D}^\sphericalangle$ is studied. We estimate the $\cosϕ_R$ asymmetry at the kinematics of COMPASS and compare with the data. The prediction at the future Electron Ion Collider (EIC) has also been presented.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Hard diffractive $\rm η_{c,b}$ hadroproduction at the LHC

In this paper, we investigate the inclusive diffractive hadroproduction for $\rm η_{c}$ and $\rm η_{b}$ at the LHC energies. Based on the NRQCD factorization formalism and the resolved-Pomeron model for the quarkonium production mechanism, we estimate the rapidity, momentum fraction loss dependence of the cross section. We give prediction ratios for single and central diffractive processes with respect to non diffractive process. These inclusive processes are sensitive to gluon content of Pomeron for small-$x$ and Reggeon for large-$x$, useful to study small and large-$x$ physics and good to test different mechanism for $\rm η_{c}$ and $\rm η_{b}$ production at the LHC. They also serve as the background to related exclusive processes thus should be predicted. Our results demonstrate that the Reggeon contribution of diffractive processes can be sizable, even sometimes dominant over Pomeron, and that its study can be useful to better constrain the Reggeon parton content. The experimental study of Reggeon can be carried out in certain kinematic windows.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Inclusive diffractive $\rm η_{c}$ production in pp, pA and AA modes at the LHC

In this paper, the inclusive Pomeron-Pomeron, Reggeon-Reggeon, Pomeron-Reggeon as well as gluon-Pomeron(-Reggeon) and photon-Pomeron(-Reggeon) interactions for the $\rm η_{c}$ at the LHC energies have been examined in proton-proton, proton-nucleus and nucleus-nucleus collision modes. The cross section has been computed based on the NRQCD factorization and Regge theory formalism. The cross exchange of Pomeron-Reggeon contribution is important in $\rm pp$ and $\rm pA$ modes. The Pomeron-Pomeron contribution is significant in $\rm AA$ mode. The Pomeron contribution is considerable for $\rm AA$ and $\rm pA$ modes in single diffractive process where $\rm A$ undergoes the diffractive process. Reggeon contribution is sizable in $\rm pp$ and $\rm pA$ modes where $\rm p$ only undergoes the diffractive process. The Pomeron and Reggeon contributions in photon-Pomeron and-Reggeon process remain smaller than that of gluon-Pomeron and-Reggeon processes. Our results show that the experimental study of Reggeon, Pomeron and their cross exchange can be carried out in certain kinematic windows with the specific choice of the mode at the LHC. The investigation can be useful to better constrain the Reggeon and Pomeron parton content. The inclusive process serves as the background to related exclusive processes which should be predicted.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

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.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Single spin asymmetry $A_{UL}^{\sin(2ϕ_h-2ϕ_R)}$ in dihadron semi-inclusive DIS

The single longitudinal spin asymmetry $A_{UL}^{\sin(2ϕ_h-2ϕ_R)}$ of dihadron production in semi-inclusive deep inelastic scattering (SIDIS) is examined through helicity-dependent dihadron fragmentation function (DiFF) $G_1^\perp$. The correlation of the longitudinal polarization of a fragmenting quark with the transverse momenta of the produced hadron pair is illustrated by this DiFF. The experimental investigation for this azimuthal asymmetry in dihadron SIDIS by the COMPASS Collaboration has lately yielded a very small signal. Here, the unknown T-odd dihadron fragmentation function $G_1^\perp$ utilizing a spectator model is computed. The model has been successfully used to describe the dihadron production in both the unpolarized and the single polarized processes to access the asymmetry and clarify why the signal is very small. The transverse momentum dependent factorization method, in which the transverse momentum of the final state hadron pair is left unintegrated, has been considered. The $\sin(2ϕ_h-2ϕ_R)$ asymmetry at the COMPASS kinematics is estimated and we compare it with the data. Besides, the predictions on the same asymmetry are also made at the HERMES and Electron Ion Collider.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Single spin asymmetry $A_{UL}^{\sin(ϕ_h-ϕ_R)}$ in dihadron semi-inclusive DIS

In this paper we study the single longitudinal spin asymmetry $A_{UL}^{\sin(ϕ_h-ϕ_R)}$ of dihadron production in semi-inclusive deep inelastic scattering (SIDIS) via helicity-dependent dihadron fragmentation function (DiFF), which describes the correlation of the longitudinal polarization of a fragmenting quark with the transverse momenta of the produced hadron pair. Recently experimental searching for this azimuthal asymmetry in dihadron SIDIS by the COMPASS Collaboration yielded a very small signal. Here we calculate this unknown T-odd DiFF $G_1^\perp$ using a spectator model to access the asymmetry and clarify why the signal is very small. The transverse momentum dependent (TMD) factorization method, in which the transverse momentum of the final state hadron pair leaves unintegrated, has been applied. We estimate the $\sin(ϕ_h-ϕ_R)$ asymmetry at the kinematics of COMPASS experiments and compare with the data. What's more, the predictions on the same asymmetry are also made at the Electron Ion Collider (EIC).

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Transverse single spin asymmetry $A_{UT}^{\sin(ϕ_h-ϕ_S)}$ for single hadron production in SIDIS

In this paper we study the single spin asymmetry $A_{UT}^{\sin(ϕ_h-ϕ_S)}$ of a single hadron production in semi-inclusive deep inelastic scattering (SIDIS) within the framework of transverse momentum dependent (TMD) factorization up to next-to-leading logarithmic (NLL) order of QCD. The asymmetry is contributed by the convolution of the Sivers function and the unpolarized fragmentation function. Specifically, the Sivers function in the coordinate space and perturbative region can be represented as the convolution of the $C$-coefficients and the corresponding collinear correlation functions, among which the Qiu-Sterman function is the most relevant one. We perform a detailed phenomenological analysis of the Sivers asymmetry at the kinematics of the HERMES and the COMPASS measurements. It is found that the obtained $x_B$-, $z_h$- and $P_{h\perp}$-dependent asymmetries are basically consistent with the HERMES and the COMPASS measurements.

0 citations0 reviewsNo code linkedOpen access
preprint2019arXiv

First-principles investigation of low-dimension MSe$_2$ (M = Ti, Hf, Zr) configurations as promising thermoelectric materials

Interest in the application of thermoelectric devices for renewable energy has risen over the past decade. In this paper, we calculate the transport properties of various configurations of the transition metal dichalcogenide (TMD) MSe$_2$ (M = Hf, Zr, Ti) in search of promising thermoelectric materials at low/high temperatures. We explore the properties of the pure monolayer at discrete levels of biaxial tensile strain (epsilon = 0%, 2%, 4%, 8%), as well as those of the van der Waals heterobilayers MSe$_2$/MSe$_2$ using first-principles calculations combined with semi-classical Boltzmann transport theory. It is found that all studied monolayers exhibit high thermoelectric performance at high temperatures, while the application of strain enhances Seebeck and thermopower non-linearly at low temperatures. The results also reveal the bilayer ZrSe$_2$/TiSe$_2$ to have remarkable thermopower at low temperatures. These findings offer insight into creating applications with enhanced performance at both low and high temperatures in future thermoelectric devices.

0 citations0 reviewsNo code linkedOpen access
preprint2019arXiv

Generation and detection of coherent longitudinal acoustic waves in ultrathin 1T'-MoTe2

Layered transition metal dichalcogenides have attracted substantial attention owing to their versatile functionalities and compatibility with current nanofabrication technologies. Thus, noninvasive means to determine the mechanical properties of nanometer (nm) thick specimens are of increasing importance. Here, we report on the detection of coherent longitudinal acoustic phonon modes generated by impulsive femtosecond (fs) optical excitation. Broadband fs-transient absorption experiments in 1T'-MoTe2 flakes as a function of thickness (7 nm - 30 nm) yield a longitudinal sound speed of 2990 m/s. In addition, temperature dependent measurements unveil a linear decrease of the normalized Young's modulus with a slope of -0.002 per K and no noticeable change caused by the Td - 1T' structural phase transition or variations in film thickness.

0 citations0 reviewsNo code linkedOpen access
preprint2019arXiv

Tuning the Catalytic Properties of Monolayer MoS2 through doping and sulfur vacancies

Fuel cells in vehicles are the leading cause of carbon monoxide emissions. CO is one of the most dangerous gases in the atmosphere, as it binds to the hemoglobin in blood cells 200 times easier than O2. As the amount of CO in the blood stream increases, the level of oxygen decreases, which can lead to many neurological problems. To reduce the amount of CO in the atmosphere, scientists have focused on the adsorption of oxygen. The best substrates used today are platinum and palladium monolayers, which are very expensive. Because of this, researchers have searched for cheap materials, such as MoS2, that are able to adsorb oxygen. However, sulfur is a chemically inert site for the oxygen, which greatly decreases the catalytic potential of monolayer MoS2 sheets. Therefore, we carried out first-principles calculations to study the effect of substitutional doping and creating sulfur vacancies on the catalytic properties of MoS2. We calculated the adsorption energy of O on doped MoS2 sheets with vacancies, and compared it to the adsorption energy of O on a Pd monolayer. We found that doping MoS2 with Ir, Rh, Co and Fe significantly decreased the adsorption energy, to below -4 eV, indicating that doped MoS2 is a more effective catalyst than Pd. Incorporating sulfur vacancies into the doped MoS2 sheet was extremely effective, and decreased the adsorption energy below -6 eV. Our results show that iridium is the best catalyst as it has the lowest adsorption energy before and after sulfur vacancies were induced. We concluded that a combination of doping and creating vacancies in monolayer MoS2 sheets can greatly impact the catalytic behavior and make it a more effective, less expensive catalyst than Pt and Pd.

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