arXiv subjects

Xiaomei Li

Publications and source records attributed to Xiaomei Li.

At least 19 recordsLinked to original sources

arXiv2026

Hyperon-Nucleon Spectrometer

Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $Λ$ polarization puzzle, in which $Λ$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse polarization that remains theoretically unexplained. This whitepaper presents the proposal for the Hyperon-Nucleon Spectrometer (H-NS) at the High-Intensity heavy-ion Accelerator Facility (HIAF). Leveraging the high energy and high intensity of HIAF's proton and heavy-ion beams, the H-NS experiment will perform systematic studies of hyperon polarization phenomena and their underlying mechanisms in proton-proton ($pp$), proton-nucleus ($pA$), and nucleus-nucleus ($AA$) collisions in the fixed target mode. A wide-range beam energy scan, including proton beams from 3 GeV up to 9.3 GeV (HIAF) and up to 32 GeV (upgraded HIAF), will be conducted to examine the dependence of polarization on collision energy. The spectrometer is designed with specialized detectors capable of high-precision reconstruction of final-state baryon polarizations. Among its many interesting and important measurements, H-NS will simultaneously measure hyperon and proton spin observables to explore the polarization mechanism in hadronic interactions and the spin structure of baryons. Furthermore, the use of $pA$ and $AA$ collisions will enable detailed investigations of cold and hot nuclear matter effects on spin polarization. Its physics program and detector development will significantly benefit the future Electron-ion Collider in China.

physics.ins-det↗

arXiv2026

Three-Dimensional Atomic-Scale Structural Transformation in a SrTiO3 Grain Boundary

Grain boundaries (GBs) in complex oxides play critical roles in governing their functional properties, which are intrinsically linked to their three-dimensional (3D) atomic configurations and local chemical environments that can deviate markedly from those of the bulk. However, the 3D atomic structures of GBs remain poorly understood due to the projection limitations of conventional (S)TEM. Here, using multislice electron ptychography, we resolve the 3D atomic structure of a Σ13(510)/[001] tilt GB in SrTiO3 with simultaneous visualization of both cation and oxygen columns. Depth-resolved reconstruction reveals pronounced structural inhomogeneity along the GB, uncovering a transition from the canonical symmetric configuration (STR1) to an asymmetric configuration (STR2) that is hidden in conventional projection imaging. Quantitative analysis of atomic-column intensities demonstrates that these two GB configurations possess distinct local chemical and vacancy distributions. By further mapping the atomic displacement fields, we reveal that the transformation between STR1 and STR2 proceeds via local atomic shuffling at the GB core and collective shear displacement in the adjoining grains, mediated by the step and dislocation character of the junction, respectively. Moreover, analysis of oxygen octahedral rotations reveals a strong dependence on the local atomic structure with pronounced asymmetry around the STR2 region. These findings establish a direct link among the 3D atomic structure, local chemical composition, and lattice order parameters at the GB, underscoring the critical importance of depth-resolved characterization in understanding and engineering GB-mediated functionalities in complex oxides.

cond-mat.mtrl-sci↗

arXiv2025

Contact line friction of bubbles

Contact line friction (CLF) of bubbles is ubiquitous, from bubbles on a beer glass to H2 bubbles sliding over electrodes in electrolysis. However, a fundamental understanding of CLF of bubbles is still missing, mainly due to the challenge of precisely controlling bubble sliding. For example, it is not clear how bubbles start sliding and how CLF of bubbles depends on velocity. We therefore developed a bubble friction force instrument to directly measure bubble CLF. This force develops from a static regime, through a transition, to a kinetic regime. This entire process is quantitatively described by a modified Kawasaki-Furmidge equation. Bubble CLF was measured for velocities from 0.2 micron/s to 2 mm/s, revealing a transition from a constant CLF regime below about 60 micron/s to a velocity-dependent CLF regime on surfaces with various wettability. The velocity dependence stems from interfacial adaptation governed by the liquid ionic environment with a relaxation time of around 10 microsecond. Moreover, CLF of bubbles can be measured on hydrophilic surfaces and under a challenging H2 atmosphere, overcoming the limitations of current droplet-based methods. Our results provide a quantitative basis for understanding CLF of bubbles with relevance to many applications, including bubble manipulation and electrochemistry.

physics.flu-dyn↗

arXiv2025

Flavor Physics at the CEPC: a General Perspective

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the $Z$ pole, the expected production of 4 Tera $Z$ bosons will provide unique and highly precise measurements of $Z$ boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean $Z$ decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and $τ$ physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The $WW$ threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals.

hep-ex↗

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↗

arXiv2025

Surfactants Screen Slide Electrification

Water drops spontaneously accumulate charges when they move on hydrophobic dielectric surfaces by slide electrification. On the one hand, slide electrification generates electricity with possible applications on tiny devices. On the other hand, the potential of up to 1 KV generated by slide electrification alters wetting and drop motion. Therefore, it is important to know the factors that affect slide electrification. To find out how surfactants affect slide electrification, we measured drop charges of aqueous drops containing cationic CTAB, anionic SDS and neutral C8E3 sliding on different hydrophobic surfaces. The result is: addition of surfactant significantly reduces the spontaneous charging of moving water drops. Based on zeta potential measurements, confocal microscopy of deposited surface-active dyes and drop impact studies, we propose that several factors contribute to this suppression of charge separation: (1) Surfactants tend to lower the contact angles, which reduces charge separation. (2) Surfactant adsorption at the solid-liquid interface can reduce the density of primary ions, particularly for anionic surfactants. (3) Anionic and neutral surfactants are mostly transferred to the liquid-air interface at the rear of the sliding drop, retaining primary ions within the drop. (4) Deposited cationic surfactant directly reduces the charge of the drop.

cond-mat.soft↗

arXiv2025

A Conceptual Framework for Human-AI Collaborative Genome Annotation

Genome annotation is essential for understanding the functional elements within genomes. While automated methods are indispensable for processing large-scale genomic data, they often face challenges in accurately predicting gene structures and functions. Consequently, manual curation by domain experts remains crucial for validating and refining these predictions. These combined outcomes from automated tools and manual curation highlight the importance of integrating human expertise with AI capabilities to improve both the accuracy and efficiency of genome annotation. However, the manual curation process is inherently labor-intensive and time-consuming, making it difficult to scale for large datasets. To address these challenges, we propose a conceptual framework, Human-AI Collaborative Genome Annotation (HAICoGA), which leverages the synergistic partnership between humans and artificial intelligence to enhance human capabilities and accelerate the genome annotation process. Additionally, we explore the potential of integrating Large Language Models (LLMs) into this framework to support and augment specific tasks. Finally, we discuss emerging challenges and outline open research questions to guide further exploration in this area.

q-bio.GN↗

arXiv2025

Signature of the $α$-clustering structure of Light Nuclei in Relativistic Nuclear Collisions

The "imaging-by-smashing" technique has been developed recently in relativistic nuclear collisions. By smashing heavy nuclei at RHIC and the LHC and analyzing the anisotropic expansion (flow) of the final state produced particles, unique information on the structure of the collided nuclei has been obtained. Existing efforts primarily focus on the colliding mode of heavy nuclei collisions. In contrast, nuclear structure studies with collisions of light nuclei and the fixed target mode, despite their significant impact and broad interest, have not been thoroughly explored. In this Letter, we investigate the $α$-clustering signature of $^{20}$Ne and $^{16}$O in the fixed-target $^{208}$Pb--$^{20}$Ne and $^{208}$Pb--$^{16}$O collisions at $\sqrt{s_{_\mathrm{NN}}}$ = 68.5 GeV, using the parton transport model AMPT. The results of two- and four-particle cumulants of anisotropic flow demonstrate a robust $α$-clustering signature that persists regardless of the complex dynamic evolution of the created systems. This study highlights the significant impact of the LHCb SMOG (SMOG2) project in discovering the $α$-clustering signature of light nuclei at relativistic energies.

nucl-th↗

arXiv2024

Prospect for measurement of the CP-violating phase $ϕ_s$ in the $B_{s}\rightarrow J/ψϕ$ channel at a future Z factory

The CP-violating phase $ϕ_s$, the \Bs decay width ($Γ_s$), and the \Bs decay width difference ($ΔΓ_s$) are sensitive probes to new physics and can constrain the heavy quark expansion theory. The potential for the measurement at future $Z$ factories is studied in this manuscript. It is found that operating at Tera-$Z$ mode, the expected precision can reach: $σ(ϕ_s) = 4.6~\mathrm{mrad}$, $σ(ΔΓ_s) = 2.4~\mathrm{ns^{-1}}$ and $σ(Γ_s) = 0.72~\mathrm{ns^{-1}}$. The precision of $ϕ_s$ is 40\% larger than the expected precision with the LHCb experiment at HL-LHC. If operating at 10-Tera-$Z$ mode, the precision of $ϕ_s$ can be measured at 45\% of the precision obtained from the LHCb experiment at HL-LHC. However, the measurement of $Γ_s$ and $ΔΓ_s$ cannot benefit from the excellent time resolution and tagging power of the future $Z$-factories. Only operating at 10-Tera-$Z$ mode can the $Γ_s$ and $ΔΓ_s$ reach an 18\% larger precision than the precision expected to be obtained from LHCb at HL-LHC. The control of penguin contamination at the future Z-factories is also discussed.

hep-ex↗

arXiv2023

Nanoscale Cathodoluminescence Spectroscopy Probing the Nitride Quantum Wells in an Electron Microcope

To gain a deeper understanding of the luminescence of multiquantum wells and the factors affecting it on a microscopic level, cathodoluminescence combined with scanning transmission electron microscopy and spectroscopy was used to reveal the luminescence of In0.15Ga0.85N five-period multiquantum wells. The composition-wave-energy relationship was established in combination with energy-dispersive X-ray spectroscopy , and the bandgaps of In0.15Ga0.85N and GaN in multiple quantum wells were extracted by electron energy loss spectroscopy to understand the features of cathodoluminescence luminescence spectra. The luminescence differences between different periods of multiquantum wells and the effects on the luminescence of multiple quantum wells owing to defects such as composition fluctuation and dislocations were revealed. Our study establishing the direct correspondence between the atomic structure of InxGa1-xN multiquantum wells and photoelectric properties, provides useful information for nitride applications.

physics.app-ph↗

arXiv2023

Atomic-Scale Tracking Phase Transition Dynamics of Berezinskii-Kosterlitz-Thouless Polar Vortex-Antivortex

Particle-like topologies, such as vortex-antivortex (V-AV) pairs, have garnered significant attention in the field of condensed matter. However, the detailed phase transition dynamics of V-AV pairs, as exemplified by self-annihilation, motion, and dissociation, have yet to be verified in real space due to the lack of suitable experimental techniques. Here, we employ polar V-AV pairs as a model system and track their transition pathways at atomic resolution with the aid of in situ (scanning) transmission electron microscopy and phase field simulations. We demonstrate the absence of a Berezinskii-Kosterlitz-Thouless phase transition between the room-temperature quasi-long-range ordered ground phase and the high-temperature disordered phase. Instead, we observe polarization suppression in bound V-AV pairs as the temperature increases. Furthermore, electric fields can promote the vortex and antivortex to approach each other and annihilate near the interface. The elucidated intermediate dynamic behaviors of polar V-AV pairs under thermal- and electrical-fields lay the foundation for their potential applications in electronic devices. Moreover, the dynamic behaviors revealed at atomic scale provide us new insights into understanding topological phase of matter and their topological phase transitions.

physics.app-ph↗

arXiv2023

Surface charge deposition by moving drops reduces contact angles

Slide electrification - the spontaneous charge separation by sliding water drops - can lead to an electrostatic potential of 1 kV and change drop motion substantially. To find out, how slide electrification influences the contact angles of moving drops, we analyzed the dynamic contact angles of aqueous drops sliding down tilted plates with insulated surfaces, grounded surfaces, and while grounding the drop. The observed decrease in dynamic contact angles at different salt concentrations is attributed to two effects: An electrocapillary reduction of contact angles caused by drop charging and a change in the free surface energy of the solid due to surface charging.

cond-mat.soft↗

arXiv2022

Electric-field control of the nucleation and motion of isolated three-fold polar vertices

Recently various topological polar structures have been discovered in oxide thin films. Despite the increasing evidence of their switchability under electrical and/or mechanical fields, the dynamic property of isolated ones, which is usually required for applications such as data storage, is still absent. Here, we show the controlled nucleation and motion of isolated three-fold vertices under an applied electric field. At the PbTiO3/SrRuO3 interface, a two-unit-cell thick SrTiO3 layer provides electrical boundary conditions for the formation of three-fold vertices. Utilizing the SrTiO3 layer and in situ electrical testing system, we find that isolated three-fold vertices can move in a controllable and reversible manner with a velocity up to ~629 nm s-1. Microstructural evolution of the nucleation and propagation of isolated three-fold vertices is further revealed by phase-field simulations. This work demonstrates the ability to electrically manipulate isolated three-fold vertices, shedding light on the dynamic property of isolated topological polar structures.

cond-mat.mtrl-sci↗

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

Tunable Interband Transitions in Twisted h-BN/Graphene Heterostructures

In twisted h-BN/graphene heterostructures, the complex electronic properties of the fast-traveling electron gas in graphene are usually considered to be fully revealed. However, the randomly twisted heterostructures may also have unexpected transition behaviors, which may influence the device performance. Here, we study the twist angle-dependent coupling effects of h-BN/graphene heterostructures using monochromatic electron energy loss spectroscopy. We find that the moiré potentials alter the band structure of graphene, resulting in a redshift of the intralayer transition at the M-point, which becomes more pronounced up to 0.25 eV with increasing twist angle. Furthermore, the twisting of the Brillouin zone of h-BN relative to the graphene M-point leads to tunable vertical transition energies in the range of 5.1-5.6 eV. Our findings indicate that twist-coupling effects of van der Waals heterostructures should be carefully considered in device fabrications, and the continuously tunable interband transitions through the twist angle can serve as a new degree of freedom to design optoelectrical devices.

cond-mat.mes-hall↗

arXiv2022

Layer-by-Layer Epitaxy of Multilayer MoS2 Wafers

Two-dimensional (2D) semiconductor of MoS2 has great potential for advanced electronics technologies beyond silicon1-9. So far, high-quality monolayer MoS2 wafers10-12 are already available and various demonstrations from individual transistors to integrated circuits have also been shown13-15. In addition to the monolayer, multilayers have narrower band gaps but improved carrier mobilities and current capacities over the monolayer5,16-18. However, achieving high-quality multilayer MoS2 wafers remains a challenge. Here we report the growth of high quality multilayer MoS2 4-inch wafers via the layer-by-layer epitaxy process. The epitaxy leads to well-defined stacking orders between adjacent epitaxial layers and offers a delicate control of layer numbers up to 6. Systematic evaluations on the atomic structures and electronic properties were carried out for achieved wafers with different layer numbers. Significant improvements on device performances were found in thicker-layer field effect transistors (FETs), as expected. For example, the average field-effect mobility (μFE) at room temperature (RT) can increase from ~80 cm2V-1s-1 for monolayer to ~110/145 cm2V-1s-1 for bilayer/trilayer devices. The highest RT μFE=234.7 cm2V-1s-1 and a record-high on-current densities of 1.704 mAμm-1 at Vds=2 V were also achieved in trilayer MoS2 FETs with a high on/off ratio exceeding 107. Our work hence moves a step closer to practical applications of 2D MoS2 in electronics.

physics.app-ph↗

arXiv2021

Engineering of Atomic-Scale Flexoelectricity at Grain Boundaries

Flexoelectricity is a type of ubiquitous and prominent electromechanical coupling, pertaining to the response of electrical polarization to mechanical strain gradients while not restricted to the symmetry of materials. However, large elastic deformation in most solids is usually difficult to achieve and the strain gradient at minuscule is challenging to control. Here we exploit the exotic structural inhomogeneity of grain boundary to achieve a huge strain gradient (~ 1.2 nm-1) within 3 ~ 4 unit-cells, and thus obtain atomic-scale flexoelectric polarization up to ~ 38 μC/cm2 at a 24 LaAlO3 grain boundary. The nanoscale flexoelectricity also modifies the electrical activity of grain boundaries. Moreover, we prove that it is a general and feasible way to form large strain gradients at atomic scale by altering the misorientation angles of grain boundaries in different dielectric materials. Thus, engineering of grain boundaries provides an effective pathway to achieve tunable flexoelectricity and broadens the electromechanical functionalities of non-piezoelectric materials.

cond-mat.mtrl-sci↗