arXiv subjects

Shuyuan Liu

Publications and source records attributed to Shuyuan Liu.

At least 19 recordsLinked to original sources

arXiv2025

Commercial Vehicle Braking Optimization: A Robust SIFT-Trajectory Approach

A vision-based trajectory analysis solution is proposed to address the "zero-speed braking" issue caused by inaccurate Controller Area Network (CAN) signals in commercial vehicle Automatic Emergency Braking (AEB) systems during low-speed operation. The algorithm utilizes the NVIDIA Jetson AGX Xavier platform to process sequential video frames from a blind spot camera, employing self-adaptive Contrast Limited Adaptive Histogram Equalization (CLAHE)-enhanced Scale-Invariant Feature Transform (SIFT) feature extraction and K-Nearest Neighbors (KNN)-Random Sample Consensus (RANSAC) matching. This allows for precise classification of the vehicle's motion state (static, vibration, moving). Key innovations include 1) multiframe trajectory displacement statistics (5-frame sliding window), 2) a dual-threshold state decision matrix, and 3) OBD-II driven dynamic Region of Interest (ROI) configuration. The system effectively suppresses environmental interference and false detection of dynamic objects, directly addressing the challenge of low-speed false activation in commercial vehicle safety systems. Evaluation in a real-world dataset (32,454 video segments from 1,852 vehicles) demonstrates an F1-score of 99.96% for static detection, 97.78% for moving state recognition, and a processing delay of 14.2 milliseconds (resolution 704x576). The deployment on-site shows an 89% reduction in false braking events, a 100% success rate in emergency braking, and a fault rate below 5%.

cs.CV↗

arXiv2025

KG-DF: A Black-box Defense Framework against Jailbreak Attacks Based on Knowledge Graphs

With the widespread application of large language models (LLMs) in various fields, the security challenges they face have become increasingly prominent, especially the issue of jailbreak. These attacks induce the model to generate erroneous or uncontrolled outputs through crafted inputs, threatening the generality and security of the model. Although existing defense methods have shown some effectiveness, they often struggle to strike a balance between model generality and security. Excessive defense may limit the normal use of the model, while insufficient defense may lead to security vulnerabilities. In response to this problem, we propose a Knowledge Graph Defense Framework (KG-DF). Specifically, because of its structured knowledge representation and semantic association capabilities, Knowledge Graph(KG) can be searched by associating input content with safe knowledge in the knowledge base, thus identifying potentially harmful intentions and providing safe reasoning paths. However, traditional KG methods encounter significant challenges in keyword extraction, particularly when confronted with diverse and evolving attack strategies. To address this issue, we introduce an extensible semantic parsing module, whose core task is to transform the input query into a set of structured and secure concept representations, thereby enhancing the relevance of the matching process. Experimental results show that our framework enhances defense performance against various jailbreak attack methods, while also improving the response quality of the LLM in general QA scenarios by incorporating domain-general knowledge.

cs.CR↗

arXiv2025

Stacking-tunable multiferroic states in bilayer ScI2

Two-dimensional(2D) multiferroic materials hold significant promise for advancing the miniaturization and integration of nanodevices. In this study, we demonstrate that 2D bilayer ScI2, which exhibits ferromagnetic(FM) ordering within each layer, enables the tuning of interlayer magnetic coupling, ferroelectricity, and valley polarization through interlayer sliding and rotation. Our first-principles calculations show that the AA stacking configuration induces antiferromagnetic (AFM) interlayer coupling, while a 180 rotation of one layer (resulting in the antialigned AA stacking) leads to FM interlayer coupling. Moreover, the interlayer magnetic coupling can be switched between AFM and FM by translating the stacking configuration: FM in the aligned AB and BA configurations, and AFM in the antialigned AB and BA configurations. This switching behavior is driven by variations in superexchange interactions due to orbital hopping between layers. Notably, the aligned stacking exhibits ferroelectricity upon sliding, which is induced by interlayer orbital hybridization and the resulting asymmetric charge redistribution, with maximal ferroelectric behavior occurring at the AB and BA stacking configurations. Additionally, for the AB and BA stackings, spontaneous valley polarization emerges from the manipulation of the spin orientation toward the out-of-plane direction. This valley polarization arises due to inversion symmetry breaking, either through ferroelectricity (in the AB and BA stackings) or AFM interlayer coupling , in combination with spin-orbit coupling. These results highlight the intricate interplay between magnetism, ferroelectricity, and valley polarization in bilayer ScI2, with each property being tunable via stacking configuration.

cond-mat.mtrl-sci↗

arXiv2025

Microscopic origin of the magnetic easy-axis switching in Fe3GaTe2 under pressure

The two-dimensional layered ferromagnet Fe3GaTe2, composed of a Te-FeI-FeII/Ga-FeI-Te stacking sequence, hosts two inequivalent Fe sites and exhibits a high Curie temperature and strong out-of-plane magneticanisotropy, making it a promising platform for spintronic applications. Recent experiments have observed a pressure-induced switching of the magnetic easy axis from out-of-plane to in-plane near 10 GPa, though its microscopic origin remains unclear. Here, we employ first-principles calculations to investigate the pressure dependence of the magnetocrystalline anisotropy energy in Fe3GaTe2. Our results reveal a clear easy-axis switching at a critical pressure of approximately 10 GPa, accompanied by a sharp decrease in the magnetic moments arising from FeI and FeII atoms. As pressure increases, spin-up and spin-down bands broaden and shift oppositely due to band dispersion effects, leading to a reduction in net magnetization. Simultaneously, the SOC contribution from FeI, which initially favors an out-of-plane easy axis, diminishes and ultimately changes sign, thereby promoting in-plane anisotropy. The SOC contribution from the outer-layer Te atoms also decreases steadily with pressure, although it retains its original sign; this additional reduction further reinforces the in-plane magnetic easy axis. In contrast, FeII atoms continue to favor an out-of-plane orientation, but their contribution is insufficient to counterbalance the dominant in-plane preference at high pressure. These findings elucidate the origin of magnetic easy-axis switching in Fe3GaTe2 and provide insights for tuning magnetic anisotropy in layered materials for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Nonreciprocal optical circuit switching

Directly switching optical signals outperforms conventional optoelectronic hardware in terms of cost, latency, and energy efficiency, and is expected to address the growing demand for data node capacity driven by the development of machine learning and artificial intelligence (AI) technologies. Therefore, optical circuit switching (OCS) technology has piqued widespread research interest in various technical solutions, including silicon photonics. However, silicon-based integrated OCS remains constrained by challenges such as network performance and port scalability. Here we propose a magneto-optical heterogeneous integrated nonreciprocal OCS (NOCS) network based on a silicon photonics platform, achieving bidirectional full-duplex nonreciprocal transmission by programming reciprocal and nonreciprocal phase shifters. We demonstrate that compared with the existing OCS architecture, NOCS has the advantages of ultra-high reconfiguration speed, large-scale integration compatibility, and bidirectional channel isolation reducing the number of required ports. NOCS could meet the programming speed requirements of the AI backend network, or supports nonreciprocal optical switching applications without multiplexing technology.

physics.optics↗

arXiv2025

Contrasting magnetic anisotropy in CrCl3 and CrBr3: A first-principles study

We present a first-principles study of the contrasting easy magnetization axes(EMAs) in the layered chromium trihalides CrCl3 and CrBr3, which exhibit in-plane and out-of-plane EMAs, respectively. Using density-functional theory calculations, we show that the EMA is determined by the interplay between spin-orbit coupling-induced magnetocrystalline anisotropy energy (SOC-MAE) and shape magnetic anisotropy energy(shape-MAE) arising from dipole-dipole interactions. While the Cr d orbitals contribute similarly to the SOC-MAE in both compounds, the key difference stems from the halogen p orbitals. In CrCl3, the localized Cl 3p orbitals favor spin-flip SOC interactions, particularly between the (px, py) and (py, pz) channels. These channels contribute with opposite signs-negative and positive, respectively-leading to partial cancellation and a small net SOC-MAE. As a result, the shape-MAE exceeds the SOC-MAE in magnitude, favoring an in-plane EMA. In contrast, CrBr3 features more delocalized Br 4p orbitals, enhanced p-d hybridization, and stronger SOC. This leads to stronger spin-conserving SOC interactions, with dominant contributions from both the (px, py) and (py, pz) channels. In this case, the positive contribution from the (px, py) channel outweighs the smaller negative contribution from the (py, pz) channel, resulting in a sizable net SOC-MAE. The SOC-MAE thus surpasses the shape-MAE and stabilizes an out-of-plane EMA. These findings demonstrate that the contrasting magnetic anisotropies in CrCl3 and CrBr3 originate from differences in the spatial distribution, SOC strength, and hybridization of the halogen p orbitals, highlighting the critical role of orbital anisotropy and spin selection rules in governing magnetic behavior in layered semiconductors.

cond-mat.mtrl-sci↗

arXiv2024

Absence of ferromagnetic instability and weak spin-orbit coupling effect in AV$_3$Sb$_5$ (A = Cs, Rb, and K)

A family of V-based kagome metals AV$_3$Sb$_5$ (A = Cs, Rb, K) presents an intriguing platform for exploring the interplay of time-reversal symmetry breaking, nontrivial topological bands, and electron correlations, resulting in a range of exotic quantum states, including the anomalous Hall effect, unconventional charge density waves, and superconductivity. These features prompt critical questions regarding the roles of magnetism and spin-orbit coupling (SOC) in these systems. Our density functional theory (DFT) calculations demonstrate a notable sensitivity of the magnetic properties to the choice of $k$-point mesh used in Brillouin zone integrations. Specifically, we find that using a dense $k$-point mesh yields a nonmagnetic pristine phase characterized by paramagnetic susceptibility, consistent with the recently observed Pauli paramagnetic behavior in single crystalline samples at high temperatures. In contrast, a coarser $k$-point mesh significantly increases the density of states at the Fermi level, inducing a ferromagnetic instability that satisfies the Stoner criterion. Moreover, our results show that the effect of SOC on both the geometric and electronic structures is minimal, with only a slight gap opening at the Dirac points, indicating a weak SOC influence in these materials. Importantly, our DFT band structure calculations closely align with angle-resolved photoemission spectroscopy data, reinforcing the notion of weak electron correlations in these kagome metals. This refined understanding challenges recent theoretical assertions that the interplay of magnetism, SOC, and electron correlations is essential for determining the nature of charge density waves in AV$_3$Sb$_5$.

cond-mat.mtrl-sci↗

arXiv2024

Exploring the Robustness of Decision-Level Through Adversarial Attacks on LLM-Based Embodied Models

Embodied intelligence empowers agents with a profound sense of perception, enabling them to respond in a manner closely aligned with real-world situations. Large Language Models (LLMs) delve into language instructions with depth, serving a crucial role in generating plans for intricate tasks. Thus, LLM-based embodied models further enhance the agent's capacity to comprehend and process information. However, this amalgamation also ushers in new challenges in the pursuit of heightened intelligence. Specifically, attackers can manipulate LLMs to produce irrelevant or even malicious outputs by altering their prompts. Confronted with this challenge, we observe a notable absence of multi-modal datasets essential for comprehensively evaluating the robustness of LLM-based embodied models. Consequently, we construct the Embodied Intelligent Robot Attack Dataset (EIRAD), tailored specifically for robustness evaluation. Additionally, two attack strategies are devised, including untargeted attacks and targeted attacks, to effectively simulate a range of diverse attack scenarios. At the same time, during the attack process, to more accurately ascertain whether our method is successful in attacking the LLM-based embodied model, we devise a new attack success evaluation method utilizing the BLIP2 model. Recognizing the time and cost-intensive nature of the GCG algorithm in attacks, we devise a scheme for prompt suffix initialization based on various target tasks, thus expediting the convergence process. Experimental results demonstrate that our method exhibits a superior attack success rate when targeting LLM-based embodied models, indicating a lower level of decision-level robustness in these models.

cs.MM↗

arXiv2024

Driving Mechanism and Dynamic Fluctuations of Charge Density Waves in the Kagome Metal ScV$_6$Sn$_6$

In a new family of V-based kagome metals RV$_6$Sn$_6$ (R = Sc, Y, La), only ScV$_6$Sn$_6$ was observed to exhibit the unusual charge density wave (CDW) with a $\sqrt{3}{\times}\sqrt{3}$ in-plane ordering and a tripling of the unit cell along the $c$-axis. However, the driving mechanism of such a $\sqrt{3}{\times}\sqrt{3}{\times}$3 CDW order is elusive. Here, using first-principles density-functional theory calculations, we demonstrate that the $\sqrt{3}{\times}\sqrt{3}{\times}$2 or $\sqrt{3}{\times}\sqrt{3}{\times}$3 CDW order is driven by a Jahn-Teller-like effect where the interlayer dimerization of Sn atoms in kagome bilayers is accompanied by a charge redistribution between such Sn atoms and its associated gap opening. It is revealed that the free energy of the $\sqrt{3}{\times}\sqrt{3}{\times}$3 phase becomes lower than that of the $\sqrt{3}{\times}\sqrt{3}{\times}$2 phase above $T_{\rm CDW}$ mostly due to the emergence of a large configurational entropy. Such a high-entropy phase shows dynamic fluctuations between its degenerate configurations but, as the temperature lowers below $T_{\rm CDW}$, it can be kinetically trapped to release a sizable entropy. Our findings not only identify the driving mechanism and order-disorder transition of the CDW in ScV$_6$Sn$_6$ but also provide an ideal platform for investigating strong CDW fluctuations in V-based kagome metals.

cond-mat.mtrl-sci↗

arXiv2022

Surface-induced ferromagnetism and anomalous Hall transport at Zr2S(001)

Two-dimensional layered electrides possessing anionic excess electrons in the interstitial spaces between cationic layers have attracted much attention due to their promising opportunities in both fundamental research and technological applications. Using first-principles calculations, we predict that the layered bulk electride Zr2S is nonmagnetic with massive Dirac nodal-line states arising from Zr-4d cationic and interlayer anionic electrons. However, the Zr2S(001) surface increases the density of states at the Fermi level caused by the surface potential, thereby inducing a ferromagnetic order at the outermost Zr layer via the Stoner instability. Consequently, the time-reversal symmetry breaking at the surface not only generates highly spin-polarized topological surface states with intricate helical spin textures, but also hosts an intrinsic anomalous Hall effect originating from the Berry curvature generated by spin-orbit coupling. Our findings offer a playground to investigate the emergence of ferromagnetism and anomalous Hall transport at the surface of nonmagnetic topological electrides.

cond-mat.mtrl-sci↗

arXiv2022

Charge density wave and superconductivity in the kagome metal CsV$_3$Sb$_5$ around a pressure-induced quantum critical point

Using first-principles density functional theory calculations, we investigate the pressure-induced quantum phase transition (QPT) from the charge density wave (CDW) to the pristine phase in the layered kagome metal CsV$_3$Sb$_5$ consisting of three-atom-thick Sb$-$V$_3$Sb$-$Sb and one-atom-thick Cs layers. The CDW structure having the formation of trimeric and hexameric V atoms with buckled Sb honeycomb layers features an increase in the lattice parameter along the $c$ axis, compared to its counterpart pristine structure having the ideal V$_3$Sb kagome and planar Sb honeycomb layers. Consequently, as pressure increases, the relatively smaller volume of the pristine phase contributes to reducing the enthalpy difference between the CDW and pristine phases, yielding a pressure-induced QPT at a critical pressure $P_c$ of ${\sim}$2 GPa. Furthermore, we find that (i) the superconducting transition temperature $T_c$ increases around $P_c$ due to a phonon softening associated with the periodic lattice distortion of V trimers and hexamers and that (ii) above $P_c$, optical phonon modes are hardened with increasing pressure, leading to monotonous decreases in the electron-phonon coupling constant and $T_c$. Our findings not only demonstrate that the uniaxial strain along the $c$ axis plays an important role in the QPT observed in CsV$_3$Sb$_5$, but also provide an explanation for the observed superconductivity around $P_c$ in terms of a phonon-mediated superconducting mechanism.

cond-mat.mtrl-sci↗

arXiv2022

Emerging Two-Dimensional Magnetism in Nonmagnetic Electrides Hf2X (X = S, Se, Te)

Recent experimental discoveries of two-dimensional (2D) magnets have triggered intense research activities to search for atomically thin magnetic systems. Using first-principles calculations, we predict the emergence of 2D magnetism in the monolayers (MLs), few layers, and surfaces of nonmagnetic layered electrides Hf2X (X = S, Se, Te) consisting of three-atom-thick Hf-X-Hf stacks. It is revealed that each bulk Hf2X hosts a novel quantum state of Dirac nodal lines with a high density of states arising from Hf-5d cationic and interlayer anionic electrons around -0.9 eV below the Fermi level EF. However, for the MLs, few layers, and surfaces of Hf2X, such hybridized states are shifted toward EF to generate van Hove singularities, leading to a Stoner instability. The resulting surface ferromagnetism gives rise to strongly spin-polarized topological surface states at Hf2X(001), demonstrating that anionic electrons, 2D magnetism, and band topology are entangled with each other. Our findings will open new perspectives for the discovery of 2D magnets via exploiting surface effects in nonmagnetic layered electrides.

cond-mat.mtrl-sci↗

arXiv2021

Electron-phonon coupling and superconductivity in an alkaline earth hydride CaH$_6$ at high pressures

Recently, an alkaline earth hydride CaH$_6$ having a sodalitelike clathrate structure has been experimentally synthesized at megabar pressures with a maximum $T_c$ of 215 K, comparable to that of a rare earth hydride LaH$_{10}$. Here, based on first-principles calculations, we find that CaH$_6$ exhibits a huge peak in the Eliashberg spectral function $α^{2}F$ around the low-frequency region of H-derived phonon modes, in contrast to LaH$_{10}$ having a widely spreading spectrum of $α^{2}F$ over the whole frequencies of H-derived phonon modes. It is revealed that the huge peak of $α^{2}F$ in CaH$_6$ is associated with an effective electron-phonon coupling (EPC) between low-frequency optical phonons and hybridized H 1$s$ and Ca 3$d$ states near the Fermi energy. As pressure increases, the strengthened H$-$H covalent bonding not only induces a hardening of optical phonon modes but also reduces the electron-phonon matrix elements related to the low-frequency optical modes, thereby leading to a lowering of the EPC constant. It is thus demonstrated that H-derived low-frequency phonon modes play an important role in the pressure-induced variation of $T_c$ in CaH$_6$. Furthermore, unlike the presence of two distinct superconducting gaps in LaH$_{10}$, CaH$_6$ is found to exhibit a single isotropic superconducting gap.

cond-mat.supr-con↗

arXiv2021

Interlayer Exchange Interaction Driven Topological Phase Transition in Antiferromagnetic Electride Gd$_2$O

Based on first-principles calculations, we discover a two-dimensional layered antiferromagnetic (AFM) electride Gd$_2$O, where anionic excess electrons exist in the interstitial spaces between positively charged cationic layers. It is revealed that each cationic layer composed of three-atom-thick Gd$-$O$-$Gd stacks has in-plane ferromagnetic and out-of-plane AFM superexchange interactions between the localized Gd 4$f$ spins through O 2$p$ orbitals. Furthermore, the interlayer superexchange mediated by the hybridized Gd-5$d$ and interstitial-$s$-like states involves intimate couplings between the spin, lattice, and charge degrees of freedom, thereby inducing simultaneous magnetic, structural, and electronic phase transitions. The resulting ground state with the simple hexagonal lattice hosts massless Dirac fermions protected by nonsymmorphic magnetic symmetry, as well as massive Dirac fermions. We thus demonstrate that the anionic excess electrons in Gd$_2$O play a crucial role in the emergence of magnetic Dirac semimetal states, therefore offering an intriguing interplay between 2D magnetic electrides and topological physics.

cond-mat.mtrl-sci↗

arXiv2021

Origin of Charge Density Wave in Layered Kagome Metal CsV$_3$Sb$_5$

Using first-principles calculations, we identify the origin of the observed charge density wave (CDW) formation in a layered kagome metal CsV$_3$Sb$_5$. It is revealed that the structural distortion of kagome lattice forming the trimeric and hexameric V atoms is accompanied by the stabilization of quasimolecular states, which gives rise to the opening of CDW gaps for the V-derived multibands lying around the Fermi level. This Jahn-Teller-like instability having the local lattice distortion and its derived quasimolecular states is a driving force of the CDW order. Specifically, the saddle points of multiple Dirac bands near the Fermi level, located at the $M$ point, are hybridized to disappear along the $k_z$ direction, therefore not supporting the widely accepted Peierls-like electronic instability due to Fermi surface nesting. It is further demonstrated that applied hydrostatic pressure significantly reduces the interlayer spacing to destabilize the quasimolecular states, leading to a disappearance of the CDW phase at a pressure of ${\sim}$2 GPa. The presently proposed underlying mechanism of the CDW order in CsV$_3$Sb$_5$ can also be applicable to other isostructural kagome lattices such as KV$_3$Sb$_5$ and RbV$_3$Sb$_5$.

cond-mat.mtrl-sci↗

arXiv2021

Formation mechanism of chemically precompressed hydrogen clathrates in metal superhydrides

Recently, the experimental discovery of high-$T_c$ superconductivity in compressed hydrides H$_3$S and LaH$_{10}$ at megabar pressures has triggered searches for various superconducting superhydrides. It was experimentally observed that thorium hydrides, ThH$_{10}$ and ThH$_9$, are stabilized at much lower pressures compared to LaH$_{10}$. Based on first-principles density-functional theory calculations, we reveal that the isolated Th frameworks of ThH$_{10}$ and ThH$_9$ have relatively more excess electrons in interstitial regions than the La framework of LaH$_{10}$. Such interstitial excess electrons easily participate in the formation of anionic H cage surrounding metal atom. The resulting Coulomb attraction between cationic Th atoms and anionic H cages is estimated to be stronger than the corresponding one of LaH$_{10}$, thereby giving rise to larger chemical precompressions in ThH$_{10}$ and ThH$_9$. Such a formation mechanism of H clathrates can also be applied to another experimentally synthesized superhydride CeH$_9$, confirming the experimental evidence that the chemical precompression in CeH$_9$ is larger than that in LaH$_{10}$. Our findings demonstrate that interstitial excess electrons in the isolated metal frameworks of high-pressure superhydrides play an important role in generating the chemical precompression of H clathrates.

cond-mat.supr-con↗

arXiv2021

Hole-Doping Effect on Superconductivity in Compressed CeH$_{9}$ at High Pressure

The experimental realization of high-temperature superconductivity in compressed hydrides H$_3$S and LaH$_{10}$ at high pressures over 150 GPa has aroused great interest in reducing the stabilization pressure of superconducting hydrides. For cerium hydride CeH$_9$ recently synthesized at 80$-$100 GPa, our first-principles calculations reveal that the strongly hybridized electronic states of Ce 4$f$ and H 1$s$ orbitals produce the topologically nontrivial Dirac nodal lines around the Fermi energy $E_F$, which are protected by crystalline symmetries. By hole doping, $E_F$ shifts down toward the topology-driven van Hove singularity to significantly increase the density of states, which in turn raises a superconducting transition temperature $T_c$ from 74 K up to 136 K at 100 GPa. The hole-doping concentration can be controlled by the incorporation of Ce$^{3+}$ ions with varying their percentages, which can be well electronically miscible with Ce atoms in the CeH$_9$ matrix because both Ce$^{3+}$ and Ce behave similarly as cations. Therefore, the interplay of symmetry, band topology, and hole doping contributes to enhance $T_c$ in compressed CeH$_9$. This mechanism to enhance $T_c$ can also be applicable to another superconducting rare earth hydride LaH$_{10}$.

cond-mat.supr-con↗

arXiv2020

Waveguide integrated high performance magneto-optical isolators and circulators on silicon nitride platforms

Optical isolators and circulators are indispensable for photonic integrated circuits (PICs). Despite of significant progress in silicon-on-insulator (SOI) platforms, integrated optical isolators and circulators have been rarely reported on silicon nitride (SiN) platforms. In this paper, we report monolithic integration of magneto-optical (MO) isolators on SiN platforms with record high performances based on standard silicon photonics foundry process and magneto-optical thin film deposition. We successfully grow high quality MO garnet thin films on SiN with large Faraday rotation up to -5900 deg/cm. We show a superior magneto-optical figure of merit (FoM) of MO/SiN waveguides compared to that of MO/SOI in an optimized device design. We demonstrate TM/TE mode broadband and narrow band optical isolators and circulators on SiN with high isolation ratio, low cross talk and low insertion loss. In particular, we observe 1 dB insertion loss and 28 dB isolation ratio in a SiN racetrack resonator-based isolator at 1570.2 nm wavelength. The low thermo-optic coefficient of SiN also ensures excellent temperature stability of the device. Our work paves the way for integration of high performance nonreciprocal photonic devices on SiN platforms.

physics.app-ph↗