arXiv subjects

Junwen Li

Publications and source records attributed to Junwen Li.

16 recordsLinked to original sources

arXiv2026

Towards Autonomous Business Intelligence via Data-to-Insight Discovery Agent

Transforming fragmented enterprise data into actionable insights remains a significant challenge for LLMs, constrained by complex database schemas, limitations in dynamic SQL generation, and the need for deep multi-dimensional analysis.In this paper, we propose AIDA(Autonomous Insight Discovery Agent), the first end-to-end framework designed for autonomous exploration in complex business environments. We establish a highly flexible instant retail environment encompassing 200+ metrics and 100+ dimensions, and integrates a proprietary Domain-Specific Language (DSL) that bridges semantic reasoning with precise SQL execution. Our reinforcement learning system subsequently formulates business analysis as a Pareto Principle-guided cumulative reasoning process. Experimental results demonstrate that AIDA significantly outperforms workflow-based agents, and extensive evaluations further reveal that AIDA achieves superior environmental perception and more in-depth analysis from diverse perspectives. Our work ultimately establishes the transformative potential of autonomous intelligence for industrial-scale business intelligence systems.

cs.AI↗

arXiv2025

Strain-Tunable Opto-electronics in PdS$_2$ Monolayer: the Role of Band Nesting and Carrier-Phonon Scattering

Strain engineering is a powerful strategy for tuning the optoelectronic properties in two-dimensional materials, yet the underlying mechanisms governing their strain response are often not fully elucidated. In this work, our first-principle calculations show that the penta-orthorhombic PdS$_2$ monolayer exhibits two key strain-tunable properties: a continuous redshift of its main optical absorption peak from $\sim$2.0 to $\sim$1.6~eV and enhancement in carrier mobility, with a more than threefold increase for electron under 0--4\% biaxial tensile strain. Subsequent analysis reveals that the tunable optical response originates from a robust band nesting feature between the highest valence and lowest conduction bands, which is preserved across the Brillouin zone under biaxial strain. For the carrier transport, deformation potential theory predicts mobility increasing with strain, strongly correlating with the reduction of carrier effective mass. Our first-principles calculations show a strain-induced monotonic decrease in carrier linewidths near the band edges, indicating suppressed carrier-phonon scattering and longer carrier lifetime as the origin of the mobility enhancement. Our work establishes a pathway for engineering the optoelectronic response in 2D semiconductors where strong band nesting governs the optical properties and paves the way for the rational design of continuously tunable flexible optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

I2CR: Intra- and Inter-modal Collaborative Reflections for Multimodal Entity Linking

Multimodal entity linking plays a crucial role in a wide range of applications. Recent advances in large language model-based methods have become the dominant paradigm for this task, effectively leveraging both textual and visual modalities to enhance performance. Despite their success, these methods still face two challenges, including unnecessary incorporation of image data in certain scenarios and the reliance only on a one-time extraction of visual features, which can undermine their effectiveness and accuracy. To address these challenges, we propose a novel LLM-based framework for the multimodal entity linking task, called Intra- and Inter-modal Collaborative Reflections. This framework prioritizes leveraging text information to address the task. When text alone is insufficient to link the correct entity through intra- and inter-modality evaluations, it employs a multi-round iterative strategy that integrates key visual clues from various aspects of the image to support reasoning and enhance matching accuracy. Extensive experiments on three widely used public datasets demonstrate that our framework consistently outperforms current state-of-the-art methods in the task, achieving improvements of 3.2%, 5.1%, and 1.6%, respectively. Our code is available at https://github.com/ziyan-xiaoyu/I2CR/.

cs.CV↗

arXiv2024

Strain-Enabled Giant Second-Order Susceptibility in Monolayer WSe$_2$

Monolayer WSe$_2$ (ML WSe$_2$) exhibits a high second-harmonic generation (SHG) efficiency under single 1-photon (1-p) or 2-photon (2-p) resonant excitation conditions due to enhanced second-order susceptibility compared with off-resonance excitation states \cite{lin2021narrow,wang2015giant}. Here, we propose a novel strain engineering approach to dramatically boost the in-plane second-order nonlinear susceptibility ($\chi_{yyy}$ ) of ML WSe$_2$ by tuning the biaxial strain to shift two K-valley excitons (the A-exciton and a high-lying exciton (HX)) into double resonance. We first identify the A-exciton and HX from the 2D Mott-Wannier model for pristine ML WSe$_2$ and calculate the $\chi_{yyy}$ under either 1-p or 2-p resonance excitations, and observe a $\sim$ 39-fold $\chi_{yyy}$ enhancement arising from the 2-p HX resonance state compared with the A-exciton case. By applying a small uniform biaxial strain (0.16\%), we observe an exciton double resonance state ($E_{\rm{HX}}$ = 2$E_{\rm{A}}$, $E_{\rm{HX}}$ and $E_{\rm{A}}$ are the exciton absorption energies), which yields up to an additional 52-fold enhancement in $\chi_{yyy}$ compared to the 2-p HX resonance state, indicating an overall $\sim$ 2000-fold enhancement compared to the single 2-p A-exciton resonance state reported in Ref \cite{wang2015giant}. Further exploration of the strain-engineered exciton states (with biaxial strain around 0.16\%) reveals that double resonance also occurs at other wavevectors near the K valley, leading to other enhancement states in $\chi_{yyy}$, confirming that strain engineering is an effective approach for enhancing $\chi_{yyy}$. Our findings suggest new avenues for strain engineering the optical properties of 2D materials for novel nonlinear optoelectronic applications.

physics.optics↗

arXiv2020

Unconventional spin-orbit torque in transition metal dichalcogenide/ferromagnet bilayers from first-principles calculations

Motivated by recent observations of unconventional out-of-plane dampinglike torque in \ch{WTe2}/Permalloy bilayer systems, we calculate the spin-orbit torque generated in two-dimensional transition metal dichalcogenide (TMD)-ferromagnet heterostructures using first-principles methods and linear response theory. Our numerical calculation of spin-orbit torques in \ch{WTe2}/Co and \ch{MoTe2}/Co heterostructures shows both conventional and novel dampinglike torkances (torque per electric field) with comparable magnitude, around $100~\hbar/2e~(\rm Ω\cdot cm)^{-1}$, for an electric field applied perpendicular to the mirror plane of the TMD layer. To gain further insight into the source of dampinglike torque, we compute the spin current flux between the TMD and Co layers and find good agreement between the two quantities. This indicates that the conventional picture of dampinglike spin-orbit torque, whereby the torque results from the spin Hall effect plus spin transfer torque, largely applies to TMD/Co bilayer systems.

cond-mat.mes-hall↗

arXiv2019

Intrinsic spin currents in ferromagnets

First principles calculations show that electric fields applied to ferromagnets generate spin currents flowing perpendicularly to the electric field. Reduced symmetry in these ferromagnets enables a wide variety of such spin currents. However, the total spin current is approximately the sum of a magnetization-independent spin Hall current and an anisotropic spin anomalous Hall current. Intrinsic spin currents are not subject to dephasing, enabling their spin polarizations to be misaligned with the magnetization, which enables the magnetization-independent spin Hall effect. The spin Hall conductivity and spin anomalous Hall conductivities of transition metal ferromagnets are comparable to those found in heavy metals, opening new avenues for efficient spin current generation in spintronic devices.

cond-mat.mes-hall↗

arXiv2017

Optical spin transfer and spin-orbit torques in thin film ferromagnets

We study the optically induced torques in thin film ferromagnetic layers under excitation by circularly polarized light. We study cases both with and without Rashba spin-orbit coupling using a 4-band model. In the absence of Rashba spin-orbit coupling, we derive an analytic expression for the optical torques, revealing the conditions under which the torque is mostly derived from optical spin transfer torque (i.e. when the torque is along the direction of optical angular momentum), versus when the torque is derived from the inverse Faraday effect (i.e. when the torque is perpendicular to the optical angular momentum). We find the optical spin transfer torque dominates provided that the excitation energy is far away from band edge transitions, and the magnetic exchange splitting is much greater than the lifetime broadening. For the case with large Rashba spin-orbit coupling and out-of-plane magnetization, we find the torque is generally perpendicular to the photon angular momentum and is ascribed to an optical Edelstein effect.

cond-mat.mes-hall↗

arXiv2016

Circular Photogalvanic Effect in Organometal Halide Perovskite CH$_3$NH$_3$PbI$_3$

We study the circular photogalvanic effect in the organometal halide perovskite solar cell absorber CH$_3$NH$_3$PbI$_3$. For crystal structures which lack inversion symmetry, the calculated photocurrent density is about $10^{-9}$ A/W, comparable to the previously studied quantum well and bulk Rashba systems. Because of the dependence of the circular photogalvanic effect on inversion symmetry breaking, the degree of inversion asymmetry at different depths from the surface can be probed by tuning the photon energy and associated penetration depth. We propose that measurements of this effect may clarify the presence or absence of inversion symmetry, which remains a controversial issue and has been argued to play an important role in the high conversion efficiency of this material.

cond-mat.mtrl-sci↗

arXiv2016

Interfacial magnetic anisotropy from a 3-dimensional Rashba substrate

We study the magnetic anisotropy which arises at the interface between a thin film ferromagnet and a 3-d Rashba material. The 3-d Rashba material is characterized by the spin-orbit strength $α$ and the direction of broken bulk inversion symmetry $\hat n$. We find an in-plane uniaxial anisotropy in the $\hat{z}\times\hat{n}$ direction, where $\hat z$ is the interface normal. For realistic values of $α$, the uniaxial anisotropy is of a similar order of magnitude as the bulk magnetocrystalline anisotropy. Evaluating the uniaxial anisotropy for a simplified model in 1-d shows that for small band filling, the in-plane easy axis anisotropy scales as $α^4$ and results from a twisted exchange interaction between the spins in the 3-d Rashba material and the ferromagnet. For a ferroelectric 3-d Rashba material, $\hat n$ can be controlled with an electric field, and we propose that the interfacial magnetic anisotropy could provide a mechanism for electrical control of the magnetic orientation.

cond-mat.mes-hall↗

arXiv2016

Optical Spintronics in Organic-Inorganic Perovskite Photovoltaics

Organic-inorganic halide CH$_3$NH$_3$PbI$_3$ solar cells have attracted enormous attention in recent years due to their remarkable power conversion efficiency. When inversion symmetry is broken, these materials should exhibit interesting spin-dependent properties as well, owing to their strong spin-orbit coupling. In this work, we consider the spin-dependent optical response of CH$_3$NH$_3$PbI$_3$. We first use density functional theory to compute the ballistic spin current generated by absorption of unpolarized light. We then consider diffusive transport of photogenerated charge and spin for a thin CH$_3$NH$_3$PbI$_3$ layer with a passivated surface and an Ohmic, non-selective contact. The spin density and spin current are evaluated by solving the drift-diffusion equations for a simplified 3-dimensional Rashba model of the electronic structure of the valence and conduction bands. We provide analytic expressions for the photon flux required to induce measurable spin densities, and propose that these spin densities can provide useful information about the role of grain boundaries in the photovoltaic behavior of these materials. We also discuss the prospects for measuring the optically generated spin current with the inverse spin Hall effect.

cond-mat.mes-hall↗

arXiv2014

MXenes as High Capacity Electrode Materials for Metal (Li, Na, K, Ca)-ion batteries

Two-dimensional (2D) materials can have an excellent capability to handle high rates of charge in ion batteries since metal ions need not diffuse in a 3D lattice structure. However graphene, which is the most important 2D material, is known to have no Li capacity. Herein, adsorption of Li, as well as Na, K, and Ca on Ti$_3$C$_2$, one representative MXene, is predicted by first-principles density functional calculations. In our study, we observed that these alkali ions exhibit different adsorption energy depending on the coverage. The adsorption energies of Na, K and Ca decrease as coverage increases, while Li shows little sensitivity to variance in coverage. This observed relationship between adsorption energies and coverage of alkali ions on Ti$_3$C$_2$ can be explained by their effective ionic radii. A larger effective ionic radius increases interaction between alkali atoms, thus lower capacity and coverage are obtained. Our calculated capacity values for Li, Na, K and Ca on Ti$_3$C$_2$ are 639.5, 319.8, 191.8 and 159.9 mAh g$^{-1}$, respectively. Compared to materials currently used in Li ion battery anodes, MXene shows great promise in increasing overall battery performance.

cond-mat.mtrl-sci↗

arXiv2013

Defective graphene as promising anode material for Na-ion battery and Ca-ion battery

We have investigated adsorption of Na and Ca on graphene with divacancy (DV) and Stone-Wales (SW) defect. Our results show that adsorption is not possible on pristine graphene. However, their adsorption on defective sheet is energetically favorable. The enhanced adsorption can be attributed to the increased charge transfer between adatoms and underlying defective sheet. With the increase in defect density until certain possible limit, maximum percentage of adsorption also increases giving higher battery capacity. For maximum possible DV defect, we can achieve maximum capacity of 1459 mAh/g for Na-ion batteries (NIBs) and 2900 mAh/g for Ca-ion batteries (CIBs). For graphene full of SW defect, we find the maximum capacity of NIBs and CIBs is around 1071 mAh/g and 2142 mAh/g respectively. Our results will help create better anode materials with much higher capacity and better cycling performance for NIBs and CIBs.

physics.chem-ph↗

arXiv2013

The Equilibrium Shape of Graphene Domains on Ni(111)

We have determined the equilibrium shape of graphene domains grown on Ni(111) via carbon segregation at 925°C. In situ, spatially-resolved electron diffraction measurements were used to determine the crystallographic orientation of the edges of the graphene domains. In contrast to recent theoretical predictions of a nearly-circular shape, we show that graphene domains, which nucleate with random shapes, all evolve toward a triangular equilibrium shape with 'zig-zag' edges. Only one of the two possible zig-zag edge orientations is observed.

cond-mat.mtrl-sci↗

arXiv2013

Bonding Charge Density and Ultimate Strength of Monolayer Transition Metal Dichalcogenides

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) can withstand a large deformation without fracture or inelastic relaxation, making them attractive for application in novel strain-engineered and flexible electronic and optoelectronic devices. In this study, we characterize the mechanical response of monolayer group VI TMDs to large elastic deformation using first-principles density functional theory calculations. We find that the ultimate strength and the overall stress response of these 2D materials is strongly influenced by their chemical composition and loading direction. We demonstrate that differences in the observed mechanical behavior can be attributed to the spatial redistribution of the occupied hybridized electronic states in the region between the transition metal atom and the chalcogens. In spite of the strong covalent bonding between the transition metal and the chalcogens, we find that a simple linear relationship can be established to describe the dependence of the mechanical strength on the charge transfer from the transition metal atom to the chalcogens.

cond-mat.mtrl-sci↗

arXiv2012

Enhanced Catalytic Activity in Strained Chemically Exfoliated WS2 Nanosheets for Hydrogen Evolution

The ability to efficiently evolve hydrogen via electrocatalysis at low overpotentials holds tremendous promise for clean energy. Hydrogen evolution reaction (HER) can be easily achieved from water if a voltage above the thermodynamic potential of the HER is applied. Large overpotentials are energetically inefficient but can be lowered with expensive platinum based catalysts. Replacement of Pt with inexpensive, earth abundant electrocatalysts would be significantly beneficial for clean and efficient hydrogen evolution. Towards this end, promising HER characteristics have been reported using 2H (trigonal prismatic) XS2 (where X = Mo or W) nanoparticles with a high concentration of metallic edges as electrocatalysts. The key challenges for HER with XS2 are increasing the number and catalytic activity of active sites. Here we report atomically thin nanosheets of chemically exfoliated WS2 as efficient catalysts for hydrogen evolution with very low overpotentials. Atomic-resolution transmission electron microscopy and spectroscopy analyses indicate that enhanced electrocatalytic activity of WS2 is associated with high concentration of strained metallic 1T (octahedral) phase in the as-exfoliated nanosheets. Density functional theory calculations reveal that the presence of strain in the 1T phase leads to an enhancement of the density of states at the Fermi level and increases the catalytic activity of the WS2 nanosheet. Our results suggest that chemically exfoliated WS2 nanosheets could be interesting catalysts for hydrogen evolution.

cond-mat.mtrl-sci↗

arXiv2010

Graphene quantum dots embedded in hexagonal boron nitride sheets

We have carried out first-principles calculations on electronic properties of graphene quantum dots embedded in hexagonal boron nitride monolayer sheets. The calculations with density functional theory show that the band gaps of quantum dots are determined by the quantum confinement effects and the hybridization of π orbitals from B, N and C atoms. The energy states near the Fermi level are found to be strongly localized within and in the vicinity of the quantum dots.

cond-mat.mes-hall↗