arXiv subjects

Tong Shi

Publications and source records attributed to Tong Shi.

At least 19 recordsLinked to original sources

arXiv2026

NMR evidence of pressure-induced structural transition and enhanced spin fluctuations up to 14~GPa in SrCu$_2$(BO$_3$)$_2$

The Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$ has attracted considerable interest as a platform for exploring quantum phases and quantum phase transitions driven by magnetic frustration. The pressure-induced structural and magnetic phase transitions in SrCu$_2$(BO$_3$)$_2$, however, remain controversial. To address this issue, we performed high-pressure $^{11}$B nuclear magnetic resonance (NMR) measurements on SrCu$_2$(BO$_3$)$_2$ up to 14~GPa. The NMR spectra reveal two pressure-induced monoclinic phases. With pressure above 4~GPa and with temperature below 10~K, the rapid broadening of the NMR spectrum and the power-law behavior in the spin-lattice relaxation rate $1/T_1$ provide clear evidence for a gapless 3D antiferromagnetic (AFM) phase in the monoclinic phase. At an intermediate temperature range around 20~K, the emergence of the field-dependent NMR line splits resolves a two-dimensional, short-range ordered AFM phase; at temperature above 30~K, the sublinear power-law behavior of $1/T_1$ identifies an extended correlated paramagnetic regime.

cond-mat.str-el↗

arXiv2026

PTQ4SNN: Membrane-Aware Post-Training Quantization for Spiking Neural Networks

Spiking neural networks (SNNs) enable sparse and event-driven computation, but their low-bit deployment remains incomplete because recurrent membrane states are commonly retained in floating point even after weight quantization. Quantizing these states is challenging because their distributions differ across channels and from the preceding weights, while small perturbations near the firing threshold may alter spike decisions and accumulate over time. We propose PTQ4SNN, a membrane-aware post-training quantization framework that jointly quantizes weights and recurrent membrane states using only a small calibration set. First, a channel-wise Unified Scale Bridge constrains the membrane scale as s_mem,c = s_w,c * 2^k_c, adapting to membrane distributions while enabling shift-compatible scale conversion. Second, Mixed-Precision Bit Allocation assigns 2/4/8-bit precision to membrane channels according to firing activity and quantization sensitivity under an average-bit budget. The framework operates on reusable projection-LIF pairs and supports both convolutional SNNs and spike-driven Transformers without backbone retraining. Experiments on static and event-based classification and semantic segmentation show that PTQ4SNN effectively preserves model accuracy under W4 quantization and approximately 4-bit membrane precision.

cs.AI↗

arXiv2026

Soft point-contact Andreev reflection spectroscopy in a palm-type cubic anvil-pressure cell

We have implemented soft point-contact Andreev reflection spectroscopy (PCARS) in a palm-type cubic anvil pressure cell by combining a substrate anchoring strategy with an external wire-splitting technique. This design enables the stable formation of multiple point contact junctions under hydrostatic pressures up to 15 GPa. Benchmark measurements on the elemental superconductor Nb demonstrate high reproducibility and yield a zero-temperature superconducting gap with a gap ratio of 3.3. We further apply this technique to the Kagome metal superconductor CsCr3Sb5 and the bilayer nickelate superconductor La2PrNi2O7. Pronounced zero-bias conductance peaks are observed, and their evolution with temperature, magnetic field and applied pressure is investigated, together with the superconducting gap magnitude and possible pairing symmetries. These measurements provide spectroscopic evidence consistent with unconventional superconductivity in these materials. Our work establishes a robust experimental platform that bridges macroscopic electrical transport and microscopic spectroscopic probes, opening a new avenue for investigating pairing symmetry in a wide range of pressure-induced unconventional superconductors.

cond-mat.supr-con↗

arXiv2026

Chiral-Structured Superconductors TrX4 (Tr = Rh, Ir; X = Ge, Si): A Platform for Mixed-Parity Pairing and Topological States

Chiral-structured superconductors, with simultaneous broken mirror and inversion symmetries, promote unconventional superconductivity through parity-mixing mechanisms. Yet a few bulk chiral-structured superconductors are known, partly due to the difficulty in directly determining their atomic-scale chirality. Here we report three chiral-structured superconductors, , RhGe4, IrGe4, and IrSi4, synthesized under high pressure, with Tc values of about 1.6 K, 1.1 K, and 2.5 K, respectively.Using atomic resolution Cs-corrected scanning transmission electron microscopy (STEM) combined with X-ray diffraction characterizations, we directly confirm their chiral structure (space group P3121). This real space imaging approach overcomes ambiguities in traditional diffraction based methods. These materials exhibit type-II superconductivity, and the enhancement of spin-orbit coupling (SOC) leads to the emergence of mixed parity pairing. Calculations also reveal symmetry protected Weyl points near the Fermi level, which is robust against the SOC. Our work not only expands the family of chiral-structured superconductors but also demonstrates the indispensable role of STEM in directly determining chiral crystal structures. These materials thus offer a clean platform to explore the interplay among structural chirality, SOC, mixed parity superconductivity, and topological quantum phenomena.

cond-mat.supr-con↗

arXiv2026

Anomalous Structural Response of Quasi-One-Dimensional Antiferromagnetic Metal KMn6Bi5 under high pressure

We report high-pressure single-crystal X-ray diffraction measurements on the quasi-one-dimensional (Q1D) antiferromagnetic metal KMn6Bi5 up to 12.5 GPa, revealing the detailed pressure evolution of its atomic coordination environment. We find that the lattice exhibits pronounced anisotropic compressibility-the relative changes in the a and b lattice parameters reach a/a0=0.91 and b/b0 = 0.94 at 12.5 GPa-and a distinct structural anomaly emerges near 11 GPa without any symmetry-breaking. Detailed structural analysis further uncovers an anomalous hardening of the Mn nanotubes between 5 and 11 GPa, followed by a configuration optimization of the Mn/Bi nanotubes around 11 GPa. These features correlate closely with the reported pressure-temperature phase diagram of KMn6Bi5 and compare favorably with the chemical pressure effects induced by substituting K with Na, Rb, or Cs. Our findings provide key microscopic insights into how coordination environment modulation governs the stability of electronic orders in low-dimensional systems.

cond-mat.mtrl-sci↗

arXiv2026

An Empirical Study of openPangu Quantization on Ascend NPUs

openPangu models are attractive targets for private and domestic large-language-model deployment, yet their robustness under aggressive post-training quantization on Ascend NPUs has not been systematically characterized. This paper conducts a controlled empirical study of openPangu 1B and 7B models on Huawei Ascend 910B1 NPUs. We evaluate representative weight-only and weight-activation post-training quantization methods, including RTN, GPTQ, AWQ, SmoothQuant, GPTAQ, BiLLM, and SliM-LLM, under a unified calibration and evaluation protocol. Across 18 evaluation tasks, we find that 8-bit weight-only quantization is effectively lossless for both models, while 4-bit quantization remains practical for the 7B model but is visibly more harmful for the 1B model on reasoning, math, and code tasks. Ultra-low precision remains challenging: most 2-bit and binary settings collapse to near-random behavior, and W4A4 SmoothQuant produces non-finite perplexity in our evaluation. These results provide an NPU-oriented accuracy map for selecting openPangu quantization settings and highlight the persistent difficulty of extreme low-bit compression.

cs.LG↗

arXiv2026

Structural responses incipient to pressure-driven antiferromagnetic quantum critical point of van der Waals heavy-fermion metal CeSiI

CeSiI is a van der Waals heavy-fermion metal recently found to exhibit unconventional superconductivity near a pressure-induced antiferromagnetic quantum critical point (QCP) at Pc =6 GPa. Here, we report a comprehensive single-crystal X-ray diffraction study of CeSiI under high pressures up to 8.3 GPa at room temperature, revealing subtle structural responses that precede pressure-driven QCP. We find that the unit-cell volume decreases smoothly upon compression without showing any structural phase transition in the investigated pressure range. Intriguingly, we observe abrupt and concurrent anisotropic responses of the lattice parameters around Pc =6 GPa, i.e., the a-axis contracts while the c-axis enlongated suddenly, with the unit-cell volume smoothily varies with pressure. Structural refinements further show that these lattice anomalies primarily originate from changes of Ce-Ce and Ce-Si bond lengths, as well as a flattening of the inner honeycomb Si layer within the CeSiI monolayer around Pc. Our findings establish an interesting case linking pressure-driven electronic transition of QCP at low temperatures to incipient structural responses at room temperature, thereby providing fresh insight into the pressure-temperature phase diagram of CeSiI.

cond-mat.str-el↗

arXiv2026

Cs$_3$V$_9$Te$_{13}$: A Correlated Electron System with Topological Flat Bands

Correlated electron systems with topological flat bands show great promise in exploring exotic quantum phenomena. However, such crystalline materials remain rare. Here we report the discovery of a novel material, Cs$_3$V$_9$Te$_{13}$, which unexpectedly exhibits magnetism and significant electron correlations. The crystal structure features two interpenetrating sets of vanadium triangles that can be linked with an ideal kagome lattice. The physical property measurements demonstrate a cascade of correlated electron phenomena, including quasi-two-dimensional bad metal, non-Fermi-liquid behavior, antiferromagnetic spin-density-wave transition at $T_\mathrm{N}$ = 47 K, possible short-range spin ordering at $\sim$350 K, a large Sommerfeld coefficient of 246 mJ mol-fu$^{-1}$ K$^{-2}$, and pressure-induced quantum criticality. These correlated electron behaviors are associated with the topological flat bands at the Fermi level, the latter of which are generated from the V2 sublattice in terms of a bipartite kagome model. Our findings establish Cs$_3$V$_9$Te$_{13}$ as a brand new correlated matter that synergistically combines flat-band physics and tunable properties.

cond-mat.str-el↗

arXiv2026

Superconductivity under pressure in the two-dimensional van der Waals heavy-fermion metal CeSiI

CeSiI is a newly discovered exfoliable van der Waals (vdW) heavy-fermion metal featured by a long-range antiferromagnetic (AF) order (TN =7.5 K) inside the Kondo coherent state below T* = 50 K. To gain a more profound understanding of the intriguing physics of this material and to uncover novel phenomena driven by quantum criticality, it is imperative to construct the phase diagram of CeSiI detailing the evolutions of T* and TN as a function of external tuning parameters such as pressure (P).In this study, we employ high pressure as an effective tuning knob to investigate this system, thereby generating a comprehensive T-P phase diagram of CeSiI. This diagram is characterized by an unusual V-shaped nonmonotonic evolution of T*(P) and the emergence of a superconducting dome with Tcmax = 240 mK upon suppression of AF order at Pc = 6 GPa, coinciding with the minimum of T*(P).The close proximity of the superconductivity (SC) to the AF instability and an unusually large upper critical field Bc2(0) exceeding 4-7 times the Pauli paramagnetic limit, suggests an unconventional pairing mechanism in CeSiI. Further analyses of normal-state transport properties provide evidence of quantum criticality, i.e., non-Fermi-liquid behavior and divergence of quasiparticle effective mass near Pc = 7 GPa. Our findings not only establish CeSiI as the first vdW heavy-fermion superconductor but also highlight an unconventional nature for the Kondo coherent state at T* at ambient pressure, hence opening a new avenue to study the interplay of strong electron correlation, Kondo hybridization, magnetism, and unconventional SC in the vdW heavy-fermion systems.

cond-mat.supr-con↗

arXiv2026

Splat-Portrait: Generalizing Talking Heads with Gaussian Splatting

Talking Head Generation aims at synthesizing natural-looking talking videos from speech and a single portrait image. Previous 3D talking head generation methods have relied on domain-specific heuristics such as warping-based facial motion representation priors to animate talking motions, yet still produce inaccurate 3D avatar reconstructions, thus undermining the realism of generated animations. We introduce Splat-Portrait, a Gaussian-splatting-based method that addresses the challenges of 3D head reconstruction and lip motion synthesis. Our approach automatically learns to disentangle a single portrait image into a static 3D reconstruction represented as static Gaussian Splatting, and a predicted whole-image 2D background. It then generates natural lip motion conditioned on input audio, without any motion driven priors. Training is driven purely by 2D reconstruction and score-distillation losses, without 3D supervision nor landmarks. Experimental results demonstrate that Splat-Portrait exhibits superior performance on talking head generation and novel view synthesis, achieving better visual quality compared to previous works. Our project code and supplementary documents are public available at https://github.com/stonewalking/Splat-portrait.

cs.CV↗

arXiv2026

Pixel-to-4D: Camera-Controlled Image-to-Video Generation with Dynamic 3D Gaussians

Humans excel at forecasting the future dynamics of a scene given just a single image. Video generation models that can mimic this ability are an essential component for intelligent systems. Recent approaches have improved temporal coherence and 3D consistency in single-image-conditioned video generation. However, these methods often lack robust user controllability, such as modifying the camera path, limiting their applicability in real-world applications. Most existing camera-controlled image-to-video models struggle with accurately modeling camera motion, maintaining temporal consistency, and preserving geometric integrity. Leveraging explicit intermediate 3D representations offers a promising solution by enabling coherent video generation aligned with a given camera trajectory. Although these methods often use 3D point clouds to render scenes and introduce object motion in a later stage, this two-step process still falls short in achieving full temporal consistency, despite allowing precise control over camera movement. We propose a novel framework that constructs a 3D Gaussian scene representation and samples plausible object motion, given a single image in a single forward pass. This enables fast, camera-guided video generation without the need for iterative denoising to inject object motion into render frames. Extensive experiments on the KITTI, Waymo, RealEstate10K and DL3DV-10K datasets demonstrate that our method achieves state-of-the-art video quality and inference efficiency. The project page is available at https://melonienimasha.github.io/Pixel-to-4D-Website.

cs.CV↗

arXiv2025

High-Resolution Modelling of Coronae and Winds in Solar-type Stars with Varying Rotation Rates I. X-ray Coronae

Stellar coronae are believed to be the main birthplace of various stellar magnetic activities. However, the structures and properties of stellar coronae remain poorly understood. Using the Space Weather Modelling Framework with the Alfv\'{e}n Wave Solar Model (SWMF-AWSoM) and dynamo-generated surface magnetic maps, here we model the coronae of four solar-type stars. By incorporating the Sun, our work covers a range of stars with the rotation varying from 1.0 to 23.3 $\Omega_\odot$ (periods of 25 to 1 days). Guided by observations, we scale the magnetic field strength with increasing rotation, covering a range between 6.0 G to 1200 G approximately. In our models, energy release associated with small-scale magnetic flux is a key source of coronal heating and is essential for reproducing realistic coronal structures. Our models capture dense (1$-$2 orders of magnitude higher than solar values) and ultra-hot ($\sim 10\,\mathrm{MK}$) coronae dominated by closed field structures. Using the CHIANTI atomic database, we also compute synthetic X-ray spectra and derive the corresponding X-ray luminosities $(L_X)$, which follow a scaling law to magnetic field $L_X \propto \langle|\mathbf{B}|\rangle^{1.75}$. Furthermore, the coronal X-ray emission is found to be rotationally modulated by the alternating presence of bright active regions and dark coronal holes. These results provide new insights into the extremely high-energy coronae of rapidly rotating solar-type stars, which differ markedly from the Sun.

astro-ph.SR↗

arXiv2025

Analysis and Simulation of Plasmons in Graphene with Time- and Space-dependent Drude Weight

We study the propagation of plasmons on graphene. The problem is considered in two dimensions with a transverse magnetic (TM) electromagnetic field. The graphene material is assumed to be flat and is modeled as a conductive sheet. This leads to a jump condition for the magnetic field on the sheet where it is related to the current density on the sheet. The current density itself satisfies Drude's law. The model then consists of Maxwell's equations coupled to current density on the sheet. To make the problem more computationally approachable, we develop a time-dependent integro-differential equation for the current density. This effectively reduces the problem to one space dimension. A finite difference method is proposed to solve the resulting equation. Numerical examples are given to illustrate previously unreported behavior of the system.

math.AP↗

arXiv2025

Strong superconducting pairing strength and pseudogap features in a putative multiphase heavy-fermion superconductor CeRh2As2 by soft point-contact spectroscopy

CeRh2As2 is a newly discovered candidate of multiphase heavy-fermion superconductor (Tc=0.3 K) with intriguing physical properties. Here, we employ soft point-contact spectroscopy to investigate its energy gap behaviors in both the normal and superconducting states. The differential conductance below Tc reveals an estimated superconducting energy gap of 2{\Delta}SC=0.24 meV and thus an extremely strong superconducting pairing strength 2{\Delta}SC/kBTc=8.8, which is comparable to those of cuprates and iron-based high-Tc superconductors as well as infinite-layer nickelates. Above Tc, a well-defined pseudogap feature is manifested as a V-shaped dip in the differential conductance spanning an energy scale of 2{\Delta}g=0.95-3.0 meV. The pseudogap feature persists to the highest characteristic temperature of Tg=8-9 K and is gradually suppressed by magnetic field of Bg=9.0T regardless of its direction relative to the crystallographic axes. The observation of pseudogap features prior to the superconducting phase transition enriches the phase diagram of CeRh2As2 and provides a novel platform to study the interplay of unconventional superconductivity and pseudogap phenomena.

cond-mat.supr-con↗

arXiv2024

Simultaneous achievement of record-breaking colossal magnetoresistance and angular magnetoresistance in an antiferromagnetic semiconductor EuSe2

Magnetoresistance effect lays the foundation for spintronics, magnetic sensors and hard drives. The pursuit of magnetic materials with colossal magnetoresistance (CMR) and/or angular magnetoresistance (AMR) has attracted enduring research interest and extensive investigations over past decades. Here we report on the discovery of field-induced record-breaking CMR of ~ -10^14 % and AMR ~ 10^14% achieved simultaneously in an antiferromagnetic rare-earth dichalcogenide EuSe2. Such intriguing observations are attributed to strong magnetic anisotropy and magnetic-field induced antiferromagnetic to ferromagnetic transition of the localized Eu2+ spins, which in turn closes the bandgap by lifting the degeneracy of Se-5p bands near Fermi level. Our DFT calculations perfectly replicate the experimental findings based on the Brillouin function and carries transport model. The present work provides a potential simple antiferromagnetic material for achieving angle-sensitive spintronic devices.

cond-mat.str-el↗

arXiv2024

A topological Hund nodal line antiferromagnet

The interplay of topology, magnetism, and correlations gives rise to intriguing phases of matter. In this study, through state-of-the-art angle-resolved photoemission spectroscopy, density functional theory and dynamical mean-field theory calculations, we visualize a fourfold degenerate Dirac nodal line at the boundary of the bulk Brillouin zone in the antiferromagnet YMn2Ge2. We further demonstrate that this gapless, antiferromagnetic Dirac nodal line is enforced by the combination of magnetism, space-time inversion symmetry and nonsymmorphic lattice symmetry. The corresponding drumhead surface states traverse the whole surface Brillouin zone. YMn2Ge2 thus serves as a platform to exhibit the interplay of multiple degenerate nodal physics and antiferromagnetism. Interestingly, the magnetic nodal line displays a d-orbital dependent renormalization along its trajectory in momentum space, thereby manifesting Hund coupling. Our findings offer insights into the effect of electronic correlations on magnetic Dirac nodal lines, leading to an antiferromagnetic Hund nodal line.

cond-mat.str-el↗

arXiv2024

Detail-Enhanced Intra- and Inter-modal Interaction for Audio-Visual Emotion Recognition

Capturing complex temporal relationships between video and audio modalities is vital for Audio-Visual Emotion Recognition (AVER). However, existing methods lack attention to local details, such as facial state changes between video frames, which can reduce the discriminability of features and thus lower recognition accuracy. In this paper, we propose a Detail-Enhanced Intra- and Inter-modal Interaction network(DE-III) for AVER, incorporating several novel aspects. We introduce optical flow information to enrich video representations with texture details that better capture facial state changes. A fusion module integrates the optical flow estimation with the corresponding video frames to enhance the representation of facial texture variations. We also design attentive intra- and inter-modal feature enhancement modules to further improve the richness and discriminability of video and audio representations. A detailed quantitative evaluation shows that our proposed model outperforms all existing methods on three benchmark datasets for both concrete and continuous emotion recognition. To encourage further research and ensure replicability, we will release our full code upon acceptance.

cs.CV↗

arXiv2021

Analyses of Laser Propagation Noises for TianQin Gravitational Wave Observatory Based on the Global Magnetosphere MHD Simulations

TianQin is a proposed space-borne gravitational wave (GW) observatory composed of three identical satellites orbiting around the geocenter with a radius of $10^5$ km. It aims at detecting GWs in the frequency range of 0.1 mHz -- 1 Hz. The detection of GW relies on the high precision measurement of optical path length at $10^{-12}$~m level. The dispersion of space plasma can lead to the optical path difference (OPD, $Δl$) along the propagation of laser beams between any pair of satellites. Here, we study the OPD noises for TianQin. The Space Weather Modeling Framework is used to simulate the interaction between the Earth magnetosphere and solar wind. From the simulations, we extract the magnetic field and plasma parameters on the orbits of TianQin at four relative positions of the satellite constellation in the Earth magnetosphere. We calculate the OPD noise for single link, Michelson combination, and Time-Delay Interferometry (TDI) combinations ($α$ and $X$). For single link and Michelson interferometer, the maxima of $|Δl|$ are on the order of 1 pm. For the TDI combinations, these can be suppressed to about 0.004 and 0.008 pm for $α$ and $X$. The OPD noise of the Michelson combination is colored in the concerned frequency range; while the ones for the TDI combinations are approximately white. Furthermore, we calculate the ratio of the equivalent strain of the OPD noise to that of TQ, and find that the OPD noises for the TDI combinations can be neglected in the most sensitive frequency range of TQ.

astro-ph.SR↗