SearcharxivSearch

arXiv subjects

Yongbin Lee

Publications and source records attributed to Yongbin Lee.

At least 19 recordsLinked to original sources

AF-Mamba: Efficient Long-Term Signal Modeling for Early Prediction of Atrial Fibrillation Onset

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with increased risks of stroke and heart failure. The growing availability of wearable and portable ECG monitoring enables continuous assessment of cardiac rhythm outside clinical settings. Predicting AF before its onset could provide additional lead time for timely clinical assessment and potentially improve the management of patients at risk of AF-related complications. This study focuses on predicting AF onset one hour in advance using long-term RR intervals (RRIs). To address this challenge, we propose a deep learning architecture that integrates temporal convolutional networks (TCNs) for local features encoding with Mamba, a selective state-space model capable of long-range sequence modeling. This hybrid TCN-Mamba design enables efficient training and inference on one-hour input windows, overcoming limitations of Transformers' quadratic scaling and recurrent networks' vanishing gradients. In subject-wise 5-fold testing, the proposed model achieved a sensitivity of 0.889, specificity of 0.943, F1-score of 0.813, AUROC of 0.974, and AUPRC of 0.933. In paired cross-dataset holdout evaluation, AF-Mamba maintained discriminative performance across unseen AF and NSR datasets, achieving a mean AUROC of 0.897. Compared against state-of-the-art AF prediction models and general time-series models, AF-Mamba achieved competitive predictive performance while providing a favorable performance-efficiency trade-off for long RRI sequences. These findings demonstrate the potential of AF-Mamba for accurate AF prediction one hour in advance and real-time continuous ambulatory monitoring.

cs.LG

A d-Electron Heavy-Fermion-Like Superconductor with Frustration-Induced Flat Bands

Heavy-fermion superconductors are mostly associated with f-electron materials with Kondo lattices, while known d-electron heavy-fermion-like systems are often linked to orbital-selective local moments, Hund-metal physics, or a charge-density-wave mechanism. Here we report Mo4PtGa17, a noncentrosymmetric itinerant d-electron superconductor with a geometrically frustrated breathing-pyrochlore Mo lattice. Thermodynamic, transport and NMR measurements reveal heavy-fermion-like behavior superconductivity and dominant ferromagnetic spin fluctuations near a ferromagnetic instability. Theoretical calculations identify nearly flat bands, van Hove singularities and Kramers nodal lines near the Fermi energy, derived intrinsically from Mo-4d states and are robust against on-site electronic correlations. These results suggest that the geometrically frustrated lattice in Mo4PtGa17 generates an intriguing electronic structure that enhances the density of states, spin susceptibility and quasiparticle mass. Mo4PtGa17 therefore identifies a unique route to heavy-fermion-like superconductivity in d-electron materials through geometrical frustration, different from the previously reported systems.

cond-mat.str-el

Memory-Efficient EDA Denoising via Knowledge Distillation for Wearable IoT Under Severe Motion Artifacts and Underwater Conditions

Electrodermal activity (EDA) is widely used in wearable Internet of Medical Things (IoMT) systems for continuous health monitoring, including autonomic assessment. However, EDA signals are highly vulnerable to motion artifacts and environmental noise, limiting reliable deployment in harsh operating conditions such as underwater. This study proposes a robust, deployable EDA denoising framework that generalizes across multiple measurement locations and harsh environments. The framework integrates a hybrid CNN-Transformer teacher model with a lightweight depth-wise separable CNN student model via a knowledge distillation (KD) strategy. To further improve robustness, a realistic data augmentation scheme is introduced to simulate diverse motion artifacts and environmental distortions. The KD-based student model significantly reduces model size (7.87 MB to 0.51 MB) and computational cost (105.1M to 11.61M FLOPs) while maintaining denoising performance (MAE: 0.144, SNR improvement: 12.08 dB) using the public dataset validation. In real-world underwater conditions (UMAC dataset) testing, the proposed method substantially improves skin conductance response reconstruction, reducing mean absolute error from 2.809 to 0.215. Furthermore, on independent testing using the CNS-OT dataset, the denoised signals enhanced downstream CNS-OT prediction performance, achieving the highest AUROC (0.806) compared to prior denoising methods. The proposed method also improved the early prediction rate (sensitivity) from 0.550 to 0.767, enabling CNS-OT prediction up to a median of 6.9 minutes before symptom onset. These results demonstrate that the proposed framework not only improves EDA signal quality but also enhances clinically relevant prediction performance while remaining suitable for deployment in resource-constrained wearable Internet of Things systems operating in harsh environments.

eess.SP

ospEDA: Orthogonal Subspace Projection for Electrodermal Activity Decomposition

Electrodermal activity (EDA) is a widely used physiological signal for assessing sympathetic nervous activity, such as arousal, stress, and pain. However, reliable decomposition into tonic and phasic components remains challenging, particularly in noisy environments and across individuals with varying signal morphologies and stimulus responses. We propose ospEDA, a novel Orthogonal Subspace Projection (OSP) based method for EDA decomposition. The method integrates (1) tonic estimation via physiologically motivated valley detection for noise robustness; (2) phasic extraction using OSP to accommodate inter subject variability; and (3) phasic driver estimation through non-negative least squares (NNLS) deconvolution with ridge regularization. We evaluated ospEDA on five real-world datasets and one simulated EDA dataset with ground-truth components, comparing its performance against six existing methods. In simulations with a 20 dB signal to noise ratio (SNR), ospEDA achieved the lowest root mean square error (RMSE) for estimated tonic (0.131) and phasic (0.132) components. Under noisier conditions (10 dB SNR), it maintained superior phasic RMSE (0.293), Pearson correlation (0.782), and R^2 (0.979) values. Furthermore, ospEDA consistently provided the highest F1 scores (0.573, 0.617, 0.638) for sympathetic nerve activity detection across 10, 20, and 30 dB SNR levels, respectively, compared to existing methods. On the real world datasets, ospEDA achieved a stimulus classification AUROC of 0.766 and consistently maintained strong effect sizes ({\omega}^2>0.14) across all five datasets. Overall, ospEDA represents a promising framework for EDA decomposition, showing generally consistent performance and reliable phasic driver estimation under the varying noise conditions, with potential utility for real world physiological monitoring applications.

eess.SP

Hidden symmetry-breaking in a kagome Ising ferromagnet

Kagome metals can host unconventional electronic phenomena that emerge from their frustrated lattice geometry and associated band topology. Correlated electronic orders, such as charge-density waves and superconductivity, are observed to intertwine with subtle time-reversal symmetry breaking whose microscopic origin is not currently understood. Here, we provide evidence for such time-reversal symmetry breaking in the kagome metal TbV$_6$Sn$_6$ arising from staggered magnetic moments within the kagome layers. TbV$_6$Sn$_6$ consists of metallic V kagome layers separated by Tb triangular layers that host Ising ferromagnetic order. Deep in the ferromagnetic state, the Tb Ising doublet ground state should display a single, dispersionless spin-flip excitation. Instead, inelastic neutron scattering reveals two sharp excitations associated with inequivalent Tb sites, demonstrating that a symmetry-broken phase coexists with Ising ferromagnetism. No additional structural or magnetic phase transitions are detected, and first-principles calculations rule out lattice distortions as the origin of the splitting. We attribute this effect to time-reversal symmetry breaking encoded by small V moments that couple to the Tb sublattice and leave a measurable spectral fingerprint. Our results establish rare-earth local moment spectroscopy as a sensitive probe of subtle broken symmetries and highlight an unexpected interplay between kagome magnetism and rare-earth local moment magnetism.

cond-mat.str-el

Atrial Fibrillation Prediction Using a Lightweight Temporal Convolutional and Selective State Space Architecture

Atrial fibrillation (AF) is the most common arrhythmia, increasing the risk of stroke, heart failure, and other cardiovascular complications. While AF detection algorithms perform well in identifying persistent AF, early-stage progression, such as paroxysmal AF (PAF), often goes undetected due to its sudden onset and short duration. However, undetected PAF can progress into sustained AF, increasing the risk of mortality and severe complications. Early prediction of AF offers an opportunity to reduce disease progression through preventive therapies, such as catecholamine-sparing agents or beta-blockers. In this study, we propose a lightweight deep learning model using only RR Intervals (RRIs), combining a Temporal Convolutional Network (TCN) for positional encoding with Mamba, a selective state space model, to enable early prediction of AF through efficient parallel sequence modeling. In subject-wise testing results, our model achieved a sensitivity of 0.908, specificity of 0.933, F1-score of 0.930, AUROC of 0.972, and AUPRC of 0.932. Additionally, our method demonstrates high computational efficiency, with only 73.5 thousand parameters and 38.3 MFLOPs, outperforming traditional Convolutional Neural Network-Recurrent Neural Network (CNN-RNN) approaches in both accuracy and model compactness. Notably, the model can predict AF up to two hours in advance using just 30 minutes of input data, providing enough lead time for preventive interventions.

cs.LG

Slow ferromagnetic fluctuations in the kagome metal Sc$_3$Mn$_3$Al$_7$Si$_5$ revealed by $^{27}$Al NMR

Static and dynamical magnetic and electronic properties of the kagome metal Sc$_3$Mn$_3$Al$_7$Si$_5$ have been investigated by $^{27}$Al nuclear magnetic resonance (NMR) measurements. The temperature dependence of Knight shift ($K$) shows a similar temperature dependence of the DC magnetic susceptibility $\chi$ except for the low-temperature region below $\sim$ 50 K where $K$ is almost constant while $\chi$ keeps increasing, which suggests that the increase in $\chi$ at low temperatures is not intrinsic. $^{27}$Al spin-lattice relaxation rate divided by temperature ($1/T_1T$) is found to be constant, confirming the metallic state of Sc$_3$Mn$_3$Al$_7$Si$_5$ from a microscopic point of view. Based on a Korringa ratio analysis using the $T_1$ and $K$ data, ferromagnetic spin fluctuations are found to dominate in Sc$_3$Mn$_3$Al$_7$Si$_5$. These fluctuations are suggested to be very slow with frequencies on the order of kilohertz or lower.

cond-mat.str-el

Giant coercivity and enhanced intrinsic anomalous Hall effect at vanishing magnetization in a compensated kagome ferrimagnet

Ferrimagnets that can be driven to magnetic compensation show promise for use in spintronics as they exhibit a finite anomalous Hall effect at zero magnetic field without having a significant magnetic moment. Compensated ferrimagnet spintronic devices with both a large anomalous Hall effect and a high coercivity would be simultaneously easy to read and difficult to erase. The kagome ferrimagnet TbMn$_6$Sn$_6$ has been reported to host a large intrinsic anomalous Hall effect. Here, we demonstrate that doping the Mn sites with Cr drives the system towards magnetic compensation. For nearly compensated compositions at low temperatures, giant coercive fields exceeding 14 T are observed. Additionally, Cr doping significantly enhances the intrinsic anomalous Hall effect, which can be attributed to a shift in the Fermi level. Our results extend the range of unique magnetic states observed in kagome materials, demonstrating that chemical doping is an effective strategy to tune and realize these states.

cond-mat.str-el

Giant Uniaxial Magnetocrystalline Anisotropy in SmCrGe$_3$

Magnetic anisotropy is a crucial characteristic for enhancing spintronic device performance. The synthesis of SmCrGe$_3$ single crystals through a high-temperature solution method has led to the determination of uniaxial magnetocrystalline anisotropy. Phase verification was achieved using scanning transmission electron microscopy (STEM), powder, and single-crystal X-ray diffraction techniques. Electrical transport and specific heat measurements indicate a Curie temperature ($T_C$) of approximately 160 K, while magnetization measurements were utilized to determine the anisotropy fields and constants. Curie-Weiss fitting applied to magnetization data suggests the contribution of both Sm and Cr in the paramagnetic phase. Additionally, density functional theory (DFT) calculations explored the electronic structures and magnetic properties of SmCrGe$_3$, revealing a significant easy-axis single-ion Sm magnetocrystalline anisotropy of 16 meV/f.u.. Based on the magnetization measurements, easy-axis magnetocrystalline anisotropy at 20 K is 13 meV/f.u..

cond-mat.mtrl-sci

Machine learning accelerated prediction of Ce-based ternary compounds involving antagonistic pairs

The discovery of novel quantum materials within ternary phase spaces containing antagonistic pair such as Fe with Bi, Pb, In, and Ag, presents significant challenges yet holds great potential. In this work, we investigate the stabilization of these immiscible pairs through the integration of Cerium (Ce), an abundant rare-earth and cost-effective element. By employing a machine learning (ML)-guided framework, particularly crystal graph convolutional neural networks (CGCNN), combined with first-principles calculations, we efficiently explore the composition/structure space and predict 9 stable and 37 metastable Ce-Fe-X (X=Bi, Pb, In and Ag) ternary compounds. Our findings include the identification of multiple new stable and metastable phases, which are evaluated for their structural and energetic properties. These discoveries not only contribute to the advancement of quantum materials but also offer viable alternatives to critical rare earth elements, underscoring the importance of Ce-based intermetallic compounds in technological applications.

cond-mat.mtrl-sci

Coexistence of Ferromagnetism and Antiferromagnetic Dimers in Topological Insulators

The addition of magnetic impurities in topological insulators can drive ferromagnetic order that leads to novel quantum anomalous Hall transport well below the Curie temperature. The fragility of the quantized regime has been ascribed to the random nature of the magnetic moment distribution. Here, we refine this hypothesis by using inelastic neutron scattering and density-functional theory calculations to show that two antagonistic components define the magnetism in Mn-substituted SnTe, thereby limiting the effectiveness of dilute magnetic TIs. One component is strongly bound antiferromagnetic dimers that compete with ferromagnetic order. The other component consists of undimerized moments where ferromagnetic order develops via long-range interactions.

cond-mat.str-el

Quantum Oscillations Measurement of the Heavy Electron Mass near the van Hove Singularity in a Kagome Metal

Kagome metals with the Fermi energy tuned near the van Hove singularities (vHss) have shown to host exotic phases including unconventional superconductivity and a chiral flux phase arising from a charge density wave. However, most quantum oscillations studies of the electronic structure of kagome metals focus on compounds which electronically or magnetically order, obscuring the unperturbed vHs. Here we present quantum oscillation measurements of YV$_6$Sn$_6$ which contains a pristine kagome lattice free from long range order. We discovered quantum oscillations corresponding to a large orbit ($\approx$70% of the Brillouin Zone area) with the heaviest mass ever observed in vanadium based kagome metals ($\approx3.3 m_e$), consistent with a Fermi pocket whose Fermi level is near the vHs. Comparing with first principles calculations suggests that the effective mass of this pocket is highly sensitive to the position of Fermi level. Our study establishes the enhanced density of states associated with a vHs in a kagome metal, allowing further insight into a potential driving mechanism for the unconventional electronic orderings in this class of materials.

cond-mat.str-el

Pseudogap behavior in charge density wave kagome material ScV$_6$Sn$_6$ revealed by magnetotransport measurements

Over the last few years, significant attention has been devoted to studying the kagome materials AV$_3$Sb$_5$ (A = K, Rb, Cs) due to their unconventional superconductivity and charge density wave (CDW) ordering. Recently ScV$_6$Sn$_6$ was found to host a CDW below $\approx$90K, and, like AV$_3$Sb$_5$, it contains a kagome lattice comprised only of V ions. Here we present a comprehensive magnetotransport study on ScV$_6$Sn$_6$. We discovered several anomalous transport phenomena above the CDW ordering temperature, including insulating behavior in interlayer resistivity, a strongly temperature-dependent Hall coefficient, and violation of Kohler's rule. All these anomalies can be consistently explained by a progressive decrease in carrier densities with decreasing temperature, suggesting the formation of a pseudogap. Our findings suggest that high-temperature CDW fluctuations play a significant role in determining the normal state electronic properties of ScV$_6$Sn$_6$.

cond-mat.str-el

Dual Nature of Magnetism Driven by Momentum Dependent f-d Kondo Hybridization

Intricate nature of magnetism in uranium-based Kondo lattices is a consequence of correlations between U-5$f$ and conduction electrons. Using linearized quasiparticle self-consistent GW plus dynamical mean-field theory, we demonstrate a crossover from incoherent to coherent $f$-$d$ Kondo cloud in the paramagnetic phase of UTe$_2$ with reduced volumes, USbTe and USbSe. As the transition occurs, we observe an augmented $f$-$d$ coherence and Pauli-like magnetic susceptibility, with a substantial frozen magnetic moment of U-5$f$ persisting. We show that momentum dependent $f$-$d$ hybridization is responsible for the magnetic moments arising from the renormalized $f$ electrons' van Hove singularity. Our findings provide a unique perspective to explain the dual nature of magnetism and the long-range magnetic ordering induced by pressure in UTe$_2$.

cond-mat.str-el

Nanoscale visualization and spectral fingerprints of the charge order in ScV6Sn6 distinct from other kagome metals

Charge density waves (CDWs) have been tied to a number of unusual phenomena in kagome metals, including rotation symmetry breaking, time-reversal symmetry breaking and superconductivity. The majority of the experiments thus far have focused on the CDW states in AV3Sb5 and FeGe, characterized by the 2a0 by 2a0 period. Recently, a bulk CDW phase (T* ~ 92 K) with a different wave length and orientation has been reported in ScV6Sn6, as the first realization of a CDW state in the broad RM6X6 structure. Here, using a combination of scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy, we reveal the microscopic structure and the spectroscopic signatures of this charge ordering phase in ScV6Sn6. Differential conductance dI/dV spectra show a partial gap opening in the density-of-states of about 20 meV at the Fermi level. This is much smaller than the spectral gaps observed in AV3Sb5 and FeGe despite the comparable T* temperatures in these systems, suggesting substantially weaker coupling strength in ScV6Sn6. Surprisingly, despite the three-dimensional bulk nature of the charge order, we find that the charge modulation is only observed on the kagome termination. Temperature-dependent band structure evolution suggests a modulation of the surface states as a consequence of the emergent charge order, with an abrupt spectral weight shift below T* consistent with the first-order phase transition. The similarity of the electronic band structures of ScV6Sn6 and TbV6Sn6 (where charge ordering is absent), together with the first-principle calculations, suggests that charge ordering in ScV6Sn6 may not be primarily electronically driven. Interestingly, in contrast to the CDW state of cousin AV3Sb5, we find no evidence supporting rotation symmetry breaking. Our results reveal a distinctive nature of the charge ordering phase in ScV6Sn6 in comparison to other kagome metals.

cond-mat.str-el

Breakdown of the scaling relation of anomalous Hall effect in Kondo lattice ferromagnet USbTe

The interaction between strong correlation and Berry curvature is an open territory of in the field of quantum materials. Here we report large anomalous Hall conductivity in a Kondo lattice ferromagnet USbTe which is dominated by intrinsic Berry curvature at low temperatures. However, the Berry curvature induced anomalous Hall effect does not follow the scaling relation derived from Fermi liquid theory. The onset of the Berry curvature contribution coincides with the Kondo coherent temperature. Combined with ARPES measurement and DMFT calculations, this strongly indicates that Berry curvature is hosted by the flat bands induced by Kondo hybridization at the Fermi level. Our results demonstrate that the Kondo coherence of the flat bands has a dramatic influence on the low temperature physical properties associated with the Berry curvature, calling for new theories of scaling relations of anomalous Hall effect to account for the interaction between strong correlation and Berry curvature.

cond-mat.str-el

Role of Magnetic Defects and Defect-engineering of Magnetic Topological Insulators

Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi$_2$Se$_3$-based dilute ferromagnetic (FM) TIs and MnBi$_2$Te$_4$ (MBT)-based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, our inelastic neutron scattering data show that a fraction of the Mn defects in Sb$_2$Te$_3$ form strong AFM dimer singlets within a quintuple block. The AFM superexchange coupling occurs via Mn-Te-Mn linear bonds and is identical to the AFM coupling between antisite defects and the FM Mn layer in MBT, establishing common interactions in the two materials classes. We also find that the FM correlations in (Sb$_{1-x}$Mn$_x$)$_2$Te$_3$ are likely driven by magnetic defects in adjacent quintuple blocks across the van der Waals gap. In addition to providing answers to long-standing questions about the evolution of FM order in dilute TI, these results also show that the evolution of global magnetic order from AFM to FM in Sb-substituted MBT is controlled by defect engineering of the intrablock and interblock coupling.

cond-mat.mtrl-sci

Short-range Crystalline Order-Tuned Conductivity in Cr$_2$Si$_2$Te$_6$ van der Waals Magnetic Crystals

Two-dimensional magnetic materials (2DMM) are significant for studies on the nature of 2D long range magnetic order but also for future spintronic devices. Of particular interest are 2DMM where spins can be manipulated by electrical conduction. Whereas Cr$_2$Si$_2$Te$_6$ exhibits magnetic order in few-layer crystals, its large band gap inhibits electronic conduction. Here we show that the defect-induced short-range crystal order in Cr$_2$Si$_2$Te$_6$ on the length scale below 0.6 nm induces substantially reduced band gap and robust semiconducting behavior down to 2 K that turns to metallic above 10 GPa. Our results will be helpful to design conducting state in 2DMM and call for spin-resolved measurement of the electronic structure in exfoliated ultrathin crystals.

cond-mat.str-el