arXiv subjects

Haiyan Lu

Publications and source records attributed to Haiyan Lu.

At least 19 recordsLinked to original sources

arXiv2026

Pressure-Driven Evolution of Electronic and Magnetic Correlations in Bilayer Nickelate La3Ni2O7

The recent discovery of high-temperature superconductivity in pressurized bilayer La3Ni2O7 has sparked intense research interest, yet the microscopic mechanism governing its pressure-dependent superconducting transition temperature (Tc) remains elusive. In this work, we investigate the electronic and magnetic correlations of La3Ni2O7 under high pressure using a combination of density-functional theory (DFT), constrained random phase approximation (cRPA), and dynamical mean-field theory (DMFT). We find that while hydrostatic pressure enhances the interlayer hopping and the bare superexchange energy scale (4t2/U), it simultaneously drives the system toward a more itinerant regime by reducing the relative correlation strength (U/W). Crucially, our results reveal a distinct orbital-selective evolution: the Ni dx2-y2 states become increasingly itinerant, whereas the Ni dz2 orbitals retain a more localized character. This pressure-induced itinerancy significantly enhances the hybridization between the two, leading to a dramatic amplification of the Kondo-like screening of the local dz2 moments by the itinerant dx2-y2 electrons. Consequently, the effective magnetic exchange coupling (Jeff), which serves as the pairing glue, is suppressed in the high-pressure regime. Our findings suggest that the monotonic decrease of Tc at high pressures is driven by the dominance of Kondo screening over superexchange interactions, providing a coherent microscopic explanation for the dome-shaped superconducting phase diagram in La3Ni2O7.

cond-mat.str-el↗

arXiv2026

Orbital-selective correlations and angular momentum coupling in heavy actinides Am, Cm, Bk, and Cf under pressure: A many-body perspective

We systematically investigate the electronic structures of americium (Am), curium (Cm), berkelium (Bk), and californium (Cf) in both the ambient-pressure double hexagonal close-packed (dhcp) and high-pressure face-centered cubic (fcc) phases, using density functional theory combined with embedded dynamical mean-field approach. Our results reveal that Am exhibits moderate correlation strength and localized 5f states dominated by jj angular momentum coupling scheme. In Cm and Bk, strong electron correlations drive the system into a localized regime, characterized by Hubbard band formation, large effective electron masses, and non-Fermi liquid behavior. Their magnetic ground states are governed by exchange interactions within an intermediate coupling scheme that shifts toward LS coupling. Remarkably, Cf reenters a jj coupling regime while exhibiting the strongest orbital-selective correlations among the series. Atomic eigenstate probabilities show moderate configurational mixing in Am, whereas Cm, Bk, and Cf maintain nearly fixed trivalent configurations, indicating localized 5f states. Compared with the dhcp phase, the fcc structure generally enhances correlation effects, as evidenced by wider Hubbard bandgaps and increased valence state fluctuation in Am. Analyses of kinetic energy, potential energy, spin susceptibility, and charge susceptibility further corroborate the progressive localization of 5f electrons and the emergence of orbital-selective correlations from Am to Cf. This work establishes a unified picture of 5f electron evolution across the Am-Cf series, elucidating the interplay between spin-orbit coupling, electron correlation, and crystal structure in heavy actinides and offering insights into their behavior under high pressure.

cond-mat.str-el↗

arXiv2025

Correlated 5f electronic states and phase stability in americium under high pressure: Insights from DFT+DMFT calculations

We investigate the electronic structure of americium (Am) across its four experimentally confirmed high-pressure phases Am-I (P63/mmc), Am-II (Fm-3m), Am-III (Fddd), and Am-IV (Pnma) up to 100 GPa, using density functional theory combined with embedded dynamical mean-field theory. Our results successfully reproduce the prominent localized 5f peak observed in ultraviolet photoelectron spectroscopy around -2.8 eV below the Fermi level in the Am-I phase. While 5f electrons in Am-I and Am-II remain strongly localized, those in Am-III and Am-IV manifest discernible signatures of increased hybridization: a noticeable shift of spectral weight toward the Fermi level, enhanced hybridization strength, and the emergence of distinct multi-peak structures. These changes indicate that 5f electrons begin to participate in bonding and undergo partial delocalization under pressure. Nevertheless, the spectral weight of 5f electrons near the Fermi level in Am-IV remains relatively low, indicating that, compared to U and Pu, Am retains stronger localized 5f electrons even under high pressure. Analysis of the electronic configurations reveals pressure-enhanced valence state fluctuation, characterized by the mixing of 5f5, 5f6, and 5f7 electronic configurations. The X-ray absorption branching ratio further shows that the angular-momentum coupling scheme approaches the jj limit. Additionally, we demonstrate that the stability of the low-symmetry high-pressure phases (Am-III and Am-IV) is governed by a Peierls-like distortion mechanism, which reduces the total energy through symmetry-lowering lattice distortions accompanied by electronic reconstruction. This study offers a new microscopic perspective on high-pressure phase transitions and emergent quantum phenomena in actinide materials.

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arXiv2025

Coop-WD: Cooperative Perception with Weighting and Denoising for Robust V2V Communication

Cooperative perception, leveraging shared information from multiple vehicles via vehicle-to-vehicle (V2V) communication, plays a vital role in autonomous driving to alleviate the limitation of single-vehicle perception. Existing works have explored the effects of V2V communication impairments on perception precision, but they lack generalization to different levels of impairments. In this work, we propose a joint weighting and denoising framework, Coop-WD, to enhance cooperative perception subject to V2V channel impairments. In this framework, the self-supervised contrastive model and the conditional diffusion probabilistic model are adopted hierarchically for vehicle-level and pixel-level feature enhancement. An efficient variant model, Coop-WD-eco, is proposed to selectively deactivate denoising to reduce processing overhead. Rician fading, non-stationarity, and time-varying distortion are considered. Simulation results demonstrate that the proposed Coop-WD outperforms conventional benchmarks in all types of channels. Qualitative analysis with visual examples further proves the superiority of our proposed method. The proposed Coop-WD-eco achieves up to 50% reduction in computational cost under severe distortion while maintaining comparable accuracy as channel conditions improve.

cs.CV↗

arXiv2024

Tracing quasiparticle dynamics and hybridization dynamics in PuCoGa5

PuCoGa5 has attracted significant attention due to its record-breaking superconducting transition temperature Tc=18.5 K among known f-electron superconductors. Here we systematically investigated the evolution of correlated electronic states in the plutonium-based unconventional superconductor PuCoGa5 upon temperature using the embedded dynamical mean-field theory merged with density functional theory. The mixed-valence nature of PuCoGa5 leads to intriguing quasiparticle dynamics and hybridization dynamics. Our findings reveal the presence of Dirac fermions and a temperature-driven localized-itinerant crossover of 5f states. As the temperature decreases, the low-energy quasiparticle resonances develop gradually, while the high-energy quasiparticle resonances exhibit quite different behaviors with an initial increase and subsequent decrease. Furthermore, we identified a characteristic temperature of approximately 290 K for the onset of hybridization gaps, which is much lower than the coherence temperature 580 K for 5f electrons. These results provide valuable insight on the the electronic structures, quasiparticle dynamics, and hybridization processes in 5f correlated electron systems.

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arXiv2024

Exotic 4f Correlated Electronic States of Ferromagnetic Kondo Lattice Compounds ReRh$_6$Ge$_4$ (Re=Ce, Ho, Er, Tm)

CeRh$_6$Ge$_4$ stands out as the first stoichiometric metallic compound with a ferromagnetic quantum critical point, thereby garnering significant attention. Ferromagnetic Kondo lattice compounds ReRh$_6$Ge$_4$ (Re=Ce, Ho, Er, Tm) have been systematically investigated with density functional theory incorporating Coulomb interaction U and spin-orbital coupling. We determined the magnetic easy axis of CeRh$_6$Ge$_4$ is within the ab plane, which is in agreement with previous magnetization measurements conducted under external magnetic field and muSR experiments. We also predicted the magnetic easy axes for the other three compounds. For TmRh$_6$Ge$_4$, the magnetic easy axis aligns along the c axis, thus preserving the $C_3$ rotational symmetry of the c axis. Especially, there are triply degenerate nodal points along the $\Gamma-A$ direction in the band structure including spin-orbital coupling. A possible localized to itinerant crossover is revealed as $4f$ electrons increase from CeRh$_6$Ge$_4$ to TmRh$_6$Ge$_4$. Specifically, the $4f$ electrons of TmRh$_6$Ge$_4$ contribute to the formation of a large Fermi surface, indicating their participation in the conduction process. Conversely, the $4f$ electrons in HoRh$_6$Ge$_4$, ErRh$_6$Ge$_4$ and CeRh$_6$Ge$_4$ remain localized, which result in smaller Fermi surfaces for these compounds. These theoretical investigations on electronic structure and magnetic properties shed deep insight into the unique nature of $4f$ electrons, providing critical predictions for subsequent experimental studies.

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arXiv2023

Novel correlated 5f electronic states in cubic AnSn3 (An=U, Np, Pu) intermetallics

The intricate interplay between itinerant-localized 5f states and strongly correlated electronic states have been systematically investigated in isostructural actinide compounds AnSn3 (An=U, Np, Pu) by using a combination of the density functional theory and the embedded dynamical mean-field approach. The obvious narrow flat 5f electronic band with remarkable spectral weight emerges in the vicinity of Fermi level for three compounds. Subsequently the significant hybridization between 5f states and conduction bands opens evident gaps together with conspicuous valence state fluctuations jointly indicating the partially itinerant 5f electrons. Especially, prominent quasiparticle multiplets only appear in PuSn3 due to the sizable valence state fluctuations and multiple competing atomic eigenstates. Therefore itinerant 5f states tend to involve in active chemical bonding, restraining the formation of local magnetic moment of actinide atoms, which partly elucidates the underlying mechanism of paramagnetic USn3 and PuSn3, as well as itinerant-electron antiferromagnetic NpSn3. Correspondingly, the 5f electronic correlation strength expressed in band renormalization and electron effective masse intertwines with itinerant-localized 5f states. Consequently, detail electronic structure of 5f states dependence on actinide series shall gain deep insight into our understanding of AnSn3 (An=U, Np, Pu) intermetallics and promote ongoing research.

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arXiv2023

DMMG: Dual Min-Max Games for Self-Supervised Skeleton-Based Action Recognition

In this work, we propose a new Dual Min-Max Games (DMMG) based self-supervised skeleton action recognition method by augmenting unlabeled data in a contrastive learning framework. Our DMMG consists of a viewpoint variation min-max game and an edge perturbation min-max game. These two min-max games adopt an adversarial paradigm to perform data augmentation on the skeleton sequences and graph-structured body joints, respectively. Our viewpoint variation min-max game focuses on constructing various hard contrastive pairs by generating skeleton sequences from various viewpoints. These hard contrastive pairs help our model learn representative action features, thus facilitating model transfer to downstream tasks. Moreover, our edge perturbation min-max game specializes in building diverse hard contrastive samples through perturbing connectivity strength among graph-based body joints. The connectivity-strength varying contrastive pairs enable the model to capture minimal sufficient information of different actions, such as representative gestures for an action while preventing the model from overfitting. By fully exploiting the proposed DMMG, we can generate sufficient challenging contrastive pairs and thus achieve discriminative action feature representations from unlabeled skeleton data in a self-supervised manner. Extensive experiments demonstrate that our method achieves superior results under various evaluation protocols on widely-used NTU-RGB+D and NTU120-RGB+D datasets.

cs.CV↗

arXiv2022

Feature Selection Approaches for Optimising Music Emotion Recognition Methods

The high feature dimensionality is a challenge in music emotion recognition. There is no common consensus on a relation between audio features and emotion. The MER system uses all available features to recognize emotion; however, this is not an optimal solution since it contains irrelevant data acting as noise. In this paper, we introduce a feature selection approach to eliminate redundant features for MER. We created a Selected Feature Set (SFS) based on the feature selection algorithm (FSA) and benchmarked it by training with two models, Support Vector Regression (SVR) and Random Forest (RF) and comparing them against with using the Complete Feature Set (CFS). The result indicates that the performance of MER has improved for both Random Forest (RF) and Support Vector Regression (SVR) models by using SFS. We found using FSA can improve performance in all scenarios, and it has potential benefits for model efficiency and stability for MER task.

cs.SD↗

arXiv2022

AFE-CNN: 3D Skeleton-based Action Recognition with Action Feature Enhancement

Existing 3D skeleton-based action recognition approaches reach impressive performance by encoding handcrafted action features to image format and decoding by CNNs. However, such methods are limited in two ways: a) the handcrafted action features are difficult to handle challenging actions, and b) they generally require complex CNN models to improve action recognition accuracy, which usually occur heavy computational burden. To overcome these limitations, we introduce a novel AFE-CNN, which devotes to enhance the features of 3D skeleton-based actions to adapt to challenging actions. We propose feature enhance modules from key joint, bone vector, key frame and temporal perspectives, thus the AFE-CNN is more robust to camera views and body sizes variation, and significantly improve the recognition accuracy on challenging actions. Moreover, our AFE-CNN adopts a light-weight CNN model to decode images with action feature enhanced, which ensures a much lower computational burden than the state-of-the-art methods. We evaluate the AFE-CNN on three benchmark skeleton-based action datasets: NTU RGB+D, NTU RGB+D 120, and UTKinect-Action3D, with extensive experimental results demonstrate our outstanding performance of AFE-CNN.

cs.CV↗

arXiv2022

PoseGU: 3D Human Pose Estimation with Novel Human Pose Generator and Unbiased Learning

3D pose estimation has recently gained substantial interests in computer vision domain. Existing 3D pose estimation methods have a strong reliance on large size well-annotated 3D pose datasets, and they suffer poor model generalization on unseen poses due to limited diversity of 3D poses in training sets. In this work, we propose PoseGU, a novel human pose generator that generates diverse poses with access only to a small size of seed samples, while equipping the Counterfactual Risk Minimization to pursue an unbiased evaluation objective. Extensive experiments demonstrate PoseGU outforms almost all the state-of-the-art 3D human pose methods under consideration over three popular benchmark datasets. Empirical analysis also proves PoseGU generates 3D poses with improved data diversity and better generalization ability.

cs.CV↗

arXiv2022

Quasiparticle multiplets and 5f electronic correlation in prototypical plutonium borides

To elucidate the localized-itinerant dual nature and orbital dependent correlations of Pu-5f valence electrons in plutonium borides (PuBx, x=1, 2, 6, 12), the electronic structures are throughout investigated by using the combination of density functional theory and single-site dynamical mean-field method. We not only reproduce the correlated topological insulator of PuB6, but also predict the metallicity in PuBx (x=1, 2, 12). It is found that the momentum-resolved spectral functions, density of states, hybridization functions all indicate partially itinerant 5f states in PuBx (x=1, 2, 6, 12). Especially, quasiparticle multiplets induced noteworthy valence state fluctuations implying the mixed-valence behavior of plutonium borides. Moreover, the itinerant degree of freedom for 5f electrons in PuBx (x=1, 2, 12) is tuned by hybridization strength between 5f states and conduction bands, which is affected by atomic distance between Pu and B atoms. Lastly, 5f electronic correlations encoded in the electron self-energy functions demonstrate moderate 5f electronic correlations in PuB6 and orbital selective 5f electronic correlations in PuBx (x=1, 2, 12). Consequently, the understanding of electronic structure and related crystal structure stability shall shed light on exploring novel 5f electrons states and ongoing experiment research.

cond-mat.str-el↗

arXiv2021

Unraveling exotic 5$f$ states and paramagnetic phase of PuSn$_3$

Plutonium-based compounds establish an ideal platform for exploring the interplay between long-standing itinerant-localized 5$f$ states and strongly correlated electronic states. In this paper, we exhaustively investigate the correlated 5$f$ electronic states of PuSn$_3$ dependence on temperature by means of a combination of the density functional theory and the embedded dynamical mean-field theory. It is found that the spectral weight of narrow 5$f$ band grows significantly and remarkable quasiparticle multiplets appear around the Fermi level at low temperature. A striking $c-f$ hybridization and prominent valence state fluctuations indicate the advent of coherence and itinerancy of 5$f$ states. It is predicted that a 5$f$ localized to itinerant crossover is induced by temperature accompanied by the change in Fermi surface topology. Therefore itinerant 5$f$ states are inclined to take in active chemical bonding, suppressing the formation of local magnetic moment of Pu atoms, which partly elucidates the intrinsic feature of paramagnetic ground state of PuSn$_3$. Furthermore, the 5$f$ electronic correlations are orbital selective manifested themselves in differentiated band renormalizations and electron effective masses. Consequently, the convincing results remain crucial to our understanding of plutonium-based compounds and promote ongoing research.

cond-mat.str-el↗

arXiv2021

Temperature-driven hidden 5f itinerant-localized crossover in heavy-fermion compound PuIn3

The temperature-dependent evolution pattern of 5f electrons helps to elucidate the long-standing itinerant-localized dual nature in plutonium-based compounds. In this work, we investigate the correlated electronic states of PuIn3 dependence on temperature by using a combination of the density functional theory and the dynamical mean-field theory. Not only the experimental photoemission spectroscopy is correctly reproduced, but also a possible hidden 5f itinerant-localized crossover is identified. Moreover, it is found that the quasiparticle multiplets from the many-body transitions gradually enhance with decreasing temperature, accompanied by the hybridizations with 5f electrons and conduction bands. The temperature-induced variation of Fermi surface topology suggests a possible electronic Lifshitz transition and the onset of magnetic order at low temperature. Finally, the ubiquitous existence orbital selective 5f electron correlation is also discovered in PuIn3. These illuminating results shall enrich the understanding on Pu-based compounds and serve as critical predictions for ongoing experimental research.

cond-mat.str-el↗

arXiv2021

Collapse of quasiparticle multiplets and $5f$ itinerant-localized crossovers in cubic phase Pu$_{3}$Ga

The physical properties of plutonium and plutonium-based intermetallic compounds are extremely sensitive to temperature, pressure, and chemical alloying. A celebrated example is the high-temperature $δ$ phase plutonium, which can be stabilized at room temperature by doping it with a few percent trivalent metal impurities, such as gallium or aluminum. The cubic phase Pu$_{3}$Ga, one of the plutonium-gallium intermetallic compounds, plays a key role in understanding the phase stability and phase transformation of the plutonium-gallium system. Its electronic structure might be essential to figure out the underlying mechanism that stabilizes the $δ$ phase plutonium-gallium alloy. In the present work, we studied the temperature-dependent correlated electronic states of cubic phase Pu$_{3}$Ga by means of a combination of the density functional theory and the embedded dynamical mean-field theory. We identified orbital selective 5$f$ itinerant-localized (coherent-incoherent) crossovers which could occur upon temperature. Actually, there exist two well-separated electronic coherent temperatures. The higher one is for the $5f_{5/2}$ state [$T_{\text{coh}}(5f_{5/2}) \approx 700$ K], while the lower one is for the $5f_{7/2}$ state [$T_{\text{coh}}(5f_{7/2}) \approx 100$ K]. In addition, the quasiparticle multiples which originate from the many-body transitions among the $5f^{4}$, $5f^{5}$, and $5f^{6}$ electronic configurations, decay gradually. The hybridizations between the localized 5$f$ bands and conduction bands are subdued by high temperature. Consequently, the Fermi surface topology is changed, which signals a temperature-driven electronic Lifshitz transition. Finally, the calculated linear specific heat coefficient $γ$ is approximately 112 mJ / (mol K$^2$) at $T = 80$ K.

cond-mat.str-el↗

arXiv2020

Temperature dependence of correlated electronic states in archetypal kagome metal CoSn

Hexagonal CoSn is a newly-discovered frustrated kagome metal. It shows close-to-textbook flat bands and orbital-selective Dirac fermions, which are largely associated with its strongly correlated Co-3$d$ orbitals. Because correlated electronic states are easily regulated by external conditions (such as chemical doping, pressure, and temperature), the fate of these kagome-derived electronic bands upon temperature becomes an interesting and unsolved question. In this work, we try to study the temperature-dependent electronic structures of hexagonal CoSn by means of the density functional theory in conjunction with the embedded dynamical mean-field theory. We find that hexagonal CoSn is in close proximity to a Mott insulating state at ambient condition. Special attention is devoted to the evolution of its Co-3$d$ electronic states with respect to temperature. At least six different temperatures (or energy scales), namely $T^{*}$, $T_{\text{FL}}$, $T_{\text{S1}}$ (and $T_{\text{S2}}$), $T_{\text{SF}}$, and $\bar{T}$, are figured out. They are related to stabilization of the "pseudogap" state, emergence of the non-Fermi-liquid phase, onset (and completeness) of the intermediate spin state, occurrence of the spin-frozen phase, beginning of the orbital freezing transition, respectively.

cond-mat.str-el↗

arXiv2020

Reexaming the ground state and magnetic properties of curium dioxide

The ground state electronic structure and magnetic behaviors of curium dioxide (CmO$_{2}$) are controversial. In general, the formal valence of Cm ions in CmO$_{2}$ should be tetravalent. It implies a $5f^{6.0}$ electronic configuration and a non-magnetic ground state. However, it is in sharp contrast with the large magnetic moment measured by painstaking experiments. In order to clarify this contradiction, we tried to study the ground state electronic structure of CmO$_{2}$ by means of a combination of density functional theory and dynamical mean-field theory. We find that CmO$_{2}$ is a wide-gap charge transfer insulator with strong 5$f$ valence state fluctuation. It belongs to a mixed-valence compound indeed. The predominant electronic configurations for Cm ions are $5f^{6.0}$ and $5f^{7.0}$. The resulting magnetic moment agrees quite well with the experimental value. Therefore, the magnetic puzzle in CmO$_{2}$ can be appropriately explained by the mixed-valence scenario.

cond-mat.str-el↗

arXiv2020

Protracted Kondo screening and kagome bands in heavy-fermion metal Ce$_{3}$Al

Ce$_{3}$Al is an archetypal heavy-fermion compound with multiple crystalline phases. Here, we try to investigate its electronic structures in the hexagonal phase ($α$-Ce$_{3}$Al) and cubic phase ($β$-Ce$_{3}$Al) by means of a combination of density functional theory and single-site dynamical mean-field theory. We confirm that the 4$f$ valence electrons in both phases are itinerant, accompanied with strong valence state fluctuations. Their 4$f$ band structures are heavily renormalized by electronic correlations, resulting in large effective electron masses. The Kondo screening in Ce$_{3}$Al would be protracted over a wide range of temperature since the single-impurity Kondo temperature $T_{K}$ is much higher than the coherent Kondo temperature $T^{*}_{K}$. Especially, the crystal structure of $α$-Ce$_{3}$Al forms a layered kagome lattice. We observe conspicuous kagome-derived flat bands and Dirac cones (or gaps) in its quasiparticle band structure. Therefore, it is concluded that the hexagonal phase of Ce$_{3}$Al will be a promising candidate of heavy-fermion kagome metal.

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