arXiv subjects

Jinlong Du

Publications and source records attributed to Jinlong Du.

13 recordsLinked to original sources

arXiv2026

VeinCast: Physics-Guided Dynamic Field Graphs with Graph-Conditioned Fusion for Global Medium-Range Weather Forecasting

Global medium-range weather forecasting requires modeling structured yet state-dependent interactions among heterogeneous atmospheric fields. Existing data-driven models largely learn these interactions implicitly, whereas equation-level physical constraints may inherit approximation and model-form biases. We present VeinCast, a physics-guided dynamic field graph and graph-conditioned fusion framework that jointly forecasts 69 surface and upper-air fields. Within each local window, its Physics-Guided Dynamic Field Graph combines predefined atmospheric relations with state-dependent Top-K residual edges and adapts Earth-window attention using the resulting graph context. Graph-Conditioned Latent Fusion further employs graph context and source-node centrality to guide field-to-latent aggregation, while bounded feedback preserves field-specific information. On the $1.5^\circ$ ERA5 benchmark, VeinCast demonstrates competitive forecasting performance across all 69 meteorological fields at lead times of up to 14 days, compared with representative global weather forecasting models including FuXi, Pangu-Weather, GraphCast, FengWu, and ARROW. Ablations confirm that the two modules provide complementary gains, demonstrating the effectiveness of relational-level physical guidance for data-driven weather forecasting.

cs.LG↗

arXiv2026

Direct observation of anisotropic exciton dispersion in the 2D semiconductor CrSBr

We report momentum-resolved measurements of exciton dispersion in multilayer CrSBr using defocus-engineered electron energy-loss spectroscopy, supported by first-principles calculations. A pronounced in-plane anisotropy is observed, with the exciton exhibiting a linear dispersion along $\Gamma$Y within $\lvert \boldsymbol{q} \rvert$ < 0.007 \r{A}$^{-1}$, while remaining nearly dispersionless along $\Gamma$X. The slope reaches 7.02 eV \r{A}, among the largest reported in low-dimensional systems. The calculations reproduce the experimentally observed linear dispersion, confirming its intrinsic origin. We attribute the anisotropic dispersion to the long-range electron--hole exchange interaction, enhanced by strong out-of-plane confinement and governed by the directional selection rules of the transition dipole moment. Comparative measurements across the magnetic phase transition from the paramagnetic to the A-type antiferromagnetic state show that the dispersion remains essentially unchanged, indicating negligible coupling between exciton propagation and magnetic order. These results establish CrSBr as a model system for investigating anisotropic exciton dynamics in low-symmetry layered semiconductors.

cond-mat.mtrl-sci↗

arXiv2026

Nanoscale Thermal Imaging of Dislocation-Mediated Heat Transport

Dislocations in crystalline materials are widely exploited to tailor the thermal conductivity of semiconductors and thermoelectrics, yet a critical gap persists: direct measurement of local thermal resistance at individual buried dislocations, along with its spatial extent, remains elusive due to the limitations of conventional thermal probes. Here, we use in situ scanning transmission electron microscopy-electron energy-loss spectroscopy to map nanoscale temperature distributions across a low-angle SrTiO3 grain boundary with periodic dislocation arrays. Our results reveal a temperature drop of 47 K across the dislocation array. The associated temperature-field distortions are concentrated near the dislocation cores, consistent with stronger local thermal resistance at these discrete sites rather than a uniformly distributed resistance along the array. We further identify a distinct two-scale heat transport characteristic near the dislocation array: core-dominated effects over approximately 4.8-6.2 nm and extended inter-core influences over approximately 10.3-14.3 nm. Atomic-scale structural and vibrational analyses further reveal core-associated atomic reconstruction and localized optical-phonon perturbations, providing a microscopic basis for the stronger local thermal resistance inferred near dislocation cores. These findings quantitatively resolve spatial heterogeneity of dislocation-mediated heat transport, uncover its atomic-scale mechanism, and provide a quantitative basis for defect engineering, guiding the design of high-performance thermoelectrics, semiconductors, high-temperature structural alloys, and other functional crystalline materials.

cond-mat.mtrl-sci↗

arXiv2025

Strongly confined Mid-infrared to Terahertz Phonon Polaritons in Ultra-thin SrTiO3

Phonon polaritons (PhPs) enable subwavelength light control for infrared sensing, imaging, and optoelectronics, but conventional polar materials have narrow Reststrahlen bands, limiting applications. Materials that support PhPs with broad spectral range, strong field confinement, slow group velocity, and high quality factor are therefore needed. Here, using monochromatic electron energy loss spectroscopy in a scanning transmission electron microscope, we demonstrate that ultra-thin SrTiO3 membranes possess the desired properties. Systematic measurements across varying thicknesses reveal two PhP branches with wide spectral dispersion, strong confinement, and anomalously slow group velocities spanning from the mid-infrared to terahertz range. Notably, in 3-nm-thick membranes, these polaritons exhibit unprecedented confinement factors exceeding 500 and group velocities as low as ~ 7 x 10-5c, rivaling the best-performing van der Waals materials. These findings establish perovskite oxide such as SrTiO3 as versatile platforms for tailoring light-matter interactions at the nanoscale, providing critical insights for the design of next-generation photonic devices requiring broadband operation and enhanced optical confinement.

physics.optics↗

arXiv2025

Single-dislocation phonons: atomic-scale measurement and their thermal properties

Nanoscale defects such as dislocations, have a significant impact on the phonon thermal transport properties in non-metallic materials. To unravel these effects, understanding of defect phonon modes is essential. Herein, at the atomic scale, the localized phonons of individual dislocation at a Si/Ge interface are measured via monochromated electron energy loss spectroscopy in a scanning transmission electron microscope. These modes are then correlated with the local microstructure, further revealing the dislocation effects on the local thermal transport properties. The dislocation causes phonon redshift in several milli-electron-volts within about two to four nanometers of the core, where both of the strain field and Ge-segregation play roles. With the presence of dislocation, the local interfacial thermal conductance can be either enhanced or reduced, depending on the complex interaction and competition between lattice-disorder (dislocation) and element-disorder (heterointerface mixing and Ge-segregation) at the interface. These findings provide valuable insights to improve the thermal properties of thermoelectric generators and thermal management systems through proper defect engineering.

cond-mat.mtrl-sci↗

arXiv2025

Resolving Phonons in Superconductor Bi2Sr2CaCu2O8+δ at Sub-Unit-Cell Resolution

The role of phonons in cuprates remains controversial, with their complex lattice structure complicating the investigation. Here, we identify phonon modes originating from charge reservoir and superconducting layers of Bi2Sr2CaCu2O8+δ using sub-unit-cell resolved electron energy loss spectroscopy in a scanning transmission electron microscope. We reveal several phonon modes exhibiting layer-specific localization: ~78 meV in-plane modes localized in the CuO2 planes, ~42 meV hybrid (in-plane and out-of-plane) modes in the CuO2 planes, and ~38 meV hybrid modes in the BiO layers. We also observe a periodic modulation of phonon frequencies induced by the superstructure, spatially correlating with the superconducting gap variation. Our findings offer new insights into the electron-phonon coupling in cuprates, fostering deeper exploration of the microscopic linkage between lattice dynamics and superconductivity.

cond-mat.supr-con↗

arXiv2023

Atomic-scale mechanism of enhanced electron-phonon coupling at the interface of MgB$_2$ thin film

In this study, we explore the heterointerface of MgB$_2$ film on SiC substrate at atomic scale using electron microscopy and spectroscopy. We detect ~1 nm MgO between MgB$_2$ and SiC. Atomic-level electron energy loss spectra (EELS) show MgB$_2$-E2g mode splitting and softening near the MgB$_2$/MgO interface. Orbital-resolved core-level EELS link the phonon softening to in-plane boron-atom electron states' changes. Ab initio calculations confirm this softening enhances electron-phonon coupling at the interface. Our findings highlight interface engineering's potential for superconductivity enhancement.

cond-mat.supr-con↗

arXiv2023

Atomic-scale observation of localized phonons at FeSe/SrTiO3 interface

In single unit-cell FeSe grown on SrTiO3, the superconductivity transition temperature features a significant enhancement. Local phonon modes at the interface associated with electron-phonon coupling may play an important role in the interface-induced enhancement. However, such phonon modes have eluded direct experimental observations. Indeed, the complicated atomic structure of the interface brings challenges to obtain the accurate structure-phonon relation knowledge from either experiment or theory, thus hindering our understanding of the enhancement mechanism. Here, we achieve direct characterizations of atomic structure and phonon modes at the FeSe/SrTiO3 interface with atomically resolved imaging and electron energy loss spectroscopy in a scanning transmission electron microscope. We find several phonon modes highly localized (~1.3 nm) at the unique double layer Ti-O termination at the interface, one of which (~ 83 meV) engages in strong interactions with the electrons in FeSe based on ab initio calculations. The electron-phonon coupling strength for such a localized interface phonon with short-range interactions is comparable to that of Fuchs-Kliewer (FK) phonon mode with long-rang interactions. Thus, our atomic-scale study provides new insights into understanding the origin of superconductivity enhancement at the FeSe/SrTiO3 interface.

cond-mat.supr-con↗

arXiv2022

Atomically localized ingredient-dependent interface phonon in heterogeneous solids

Phonons are the primary heat carriers in non-metallic solids. In compositionally heterogeneous materials, the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder and strain fluctuations, while the effects of compositional fluctuation induced local phonon states are usually ignored. Here, by scanning transmission electron microscopy electron energy loss spectroscopy and sophisticated calculations, we identify the vibrational properties of ingredient-dependent interface phonon modes in AlxGa1-xN and quantify their various contributions to the local interface thermal conductance. We demonstrate that atomic-scale compositional fluctuation has significant influence on the vibrational thermodynamic properties, highly affecting the mode ratio and vibrational amplitude of interface phonon modes and subsequently redistributing their modal contribution to the ITC. Our work provides fundamental insights into understanding of local phonon-boundary interactions in nanoscale inhomogeneities, which reveal new opportunities for optimization of thermal properties via engineering ingredient distribution.

cond-mat.mtrl-sci↗

arXiv2022

Electron microscopy probing electron-photon interactions in SiC nanowires with ultra-wide energy and momentum match

Nanoscale materials usually can trap light and strongly interact with it leading to many photonic device applications. The light-matter interactions are commonly probed by optical spectroscopy, which, however, have some limitations such as diffraction-limited spatial resolution, tiny momentum transfer and non-continuous excitation/detection. In this work, using scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) with ultra-wide energy and momentum match and sub-nanometer spatial resolution, we study the optical microcavity resonant spectroscopy in a single SiC nanowire. The longitudinal Fabry-Perot (FP) resonating modes and the transverse whispering-gallery modes (WGMs) are simultaneously excited and detected, which span from near-infrared (~ 1.2 μm) to ultraviolet (~ 0.2 μm) spectral regime and the momentum transfer can be ranging up to 108 cm{^{-1}}. The size effects on the resonant spectra of nanowires are also revealed. Moreover, the nanoscale decay length of resonant EELS is revealed, which is contributed by the strongly localized electron-photon interactions in the SiC nanowire. This work provides a new alternative technique to investigate the optical resonating spectroscopy of a single nanowire structure and to explore the light-matter interactions in dielectric nanostructures, which is also promising for modulating free electrons via photonic structures.

cond-mat.mes-hall↗

arXiv2022

Direct observation of local antiferroelectricity induced phonon softening at a SrTiO3 defect

Defects in oxides usually exhibit exotic properties that may be associated with the local lattice dynamics. Here, at atomic spatial resolution, we directly measure phonon modes of an antiphase boundary (APB) in SrTiO3 freestanding membrane and correlate them with the picometer-level structural distortion. We find that the SrTiO3 APB introduces new defect phonon modes that are absent in bulk SrTiO3. These modes are highly sensitive to the subtle structure distortion, i.e., the SrTiO3 APB generates the local electric dipoles forming an antiferroelectric configuration, which significantly softens the transverse optical (TO) and longitudinal optical (LO) modes at Γ point. Correlating the local phonons with the subtle structural distortion, our findings provide valuable insights into understanding the defect properties in complex oxides and essential information for their applications such as thermoelectric devices.

cond-mat.mtrl-sci↗

arXiv2021

Measuring phonon dispersion at an interface

The breakdown of translational symmetry at heterointerfaces leads to the emergence of new phonon modes localized near the interface. These interface phonons play an essential role in thermal/electrical transport properties in devices especially in miniature ones wherein the interface may dominate the entire response of the device. Knowledge of phonon dispersion at interfaces is therefore highly desirable for device design and optimization. Although theoretical work has begun decades ago, experimental research is totally absent due to challenges in achieving combined spatial, momentum and spectral resolutions required to probe localized phonon modes. Here we use electron energy loss spectroscopy in an electron microscope to directly measure both the local phonon density of states and the interface phonon dispersion relation for an epitaxial cBN-diamond heterointerface. In addition to bulk phonon modes, we observe acoustic and optical phonon modes localized at the interface, and modes isolated away from the interface. These features only appear within ~ 1 nm around the interface. The experimental results can be nicely reproduced by ab initio calculations. Our findings provide insights into lattice dynamics at heterointerfaces and should be practically useful in thermal/electrical engineering.

cond-mat.mtrl-sci↗

arXiv2020

Four-dimensional Vibrational Spectroscopy for Nanoscale Mapping of Phonon Dispersion in BN Nanotubes

Direct measurement of local phonon dispersion in individual nanostructures can greatly advance our understanding of their electrical, thermal, and mechanical properties. However, such experimental measurements require extremely high detection sensitivity and combined spatial, energy and momentum resolutions, thus has been elusive. Here, we develop a four-dimensional electron energy loss spectroscopy (4D-EELS) technique based a monochromated scanning transmission electron microscope (STEM), and present the position-dependent phonon dispersion measurement in individual boron nitride nanotubes (BNNTs). Our measurement shows that the unfolded phonon dispersion of multi-walled BNNTs is close to hexagonal-boron nitride (h-BN) crystals, suggesting that interlayer coupling and curved geometry have no substantial impacts on phonon dispersion. We also find that the acoustic phonons are extremely sensitive to momentum-dependent defect scattering, while optical phonons are much less susceptible. This work not only provides useful insights into vibrational properties of BNNTs, but also demonstrates huge prospects of the developed 4D-EELS technique in nanoscale phonon dispersion measurements.

cond-mat.mes-hall↗