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Jinwoong Kim

Jinwoong Kim appears in the imported research catalog. Authorship, coauthor and topic links are available while profile ownership is still unclaimed.

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cond-mat.mtrl-scicond-mat.mes-hallArtificial IntelligenceMachine LearningComputation and LanguageComputer Science and Game Theorycond-mat.othercond-mat.str-el

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Published work

12 published item(s)

preprint2026arXiv

GeoBuildBench: A Benchmark for Interactive and Executable Geometry Construction from Natural Language

We introduce GeoBuildBench, a benchmark designed to evaluate whether large language models and multimodal agents can ground informal natural-language plane geometry problems into executable geometric constructions. Unlike existing geometry benchmarks that focus on answer correctness or static diagram interpretation, GeoBuildBench treats geometry diagram as an interactive construction task: given a textual problem, an agent must generate a domain-specific language (DSL) program to produce a diagram satisfying explicitly specified geometric objects and verifiable constraints. The benchmark features 489 Chinese textbook-style problems, curated through automated filtering and human validation to ensure text-complete, constructible problem specifications. We evaluate several state-of-the-art multimodal models in a bounded iterative setting and show that, despite reasonable success rates, models frequently exhibit structural hallucinations, missing objects, and failures to satisfy geometric constraints, with limited ability to exploit visual and constraint-based feedback for self-correction. These results highlight geometry construction as a rigorous testbed for grounded, executable reasoning beyond textual or visual plausibility. Our benchmark and code are publicly available.

0 citations0 reviewsNo code linkedOpen access
preprint2026arXiv

GroupSegment-SHAP: Shapley Value Explanations with Group-Segment Players for Multivariate Time Series

Multivariate time-series models achieve strong predictive performance in healthcare, industry, energy, and finance, but how they combine cross-variable interactions with temporal dynamics remains unclear. SHapley Additive exPlanations (SHAP) are widely used for interpretation. However, existing time-series variants typically treat the feature and time axes independently, fragmenting structural signals formed jointly by multiple variables over specific intervals. We propose GroupSegment SHAP (GS-SHAP), which constructs explanatory units as group-segment players based on cross-variable dependence and distribution shifts over time, and then quantifies each unit's contribution via Shapley attribution. We evaluate GS-SHAP across four real-world domains: human activity recognition, power-system forecasting, medical signal analysis, and financial time series, and compare it with KernelSHAP, TimeSHAP, SequenceSHAP, WindowSHAP, and TSHAP. GS-SHAP improves deletion-based faithfulness (DeltaAUC) by about 1.7x on average over time-series SHAP baselines, while reducing wall-clock runtime by about 40 percent on average under matched perturbation budgets. A financial case study shows that GS-SHAP identifies interpretable multivariate-temporal interactions among key market variables during high-volatility regimes.

0 citations0 reviewsNo code linkedOpen access
preprint2026arXiv

ReTAMamba: Reliability-Aware Temporal Aggregation with Mamba for Irregular Clinical Time Series Prediction

Clinical time-series data are difficult to model with methods designed for regular sequences because they exhibit irregular sampling, frequent missing values, and heterogeneous observation patterns across variables. Existing approaches commonly use observation masks and time-gap information, but they do not continuously capture the decaying reliability of past observations or consistently organize multi-resolution information within a coherent temporal context during aggregation. To address these limitations, we propose Reliability-aware Temporal Aggregation with Mamba (ReTAMamba), which reconstructs clinical time series as time-variable token sequences, estimates observation reliability from missingness and elapsed time, and augments interval summaries with statistical descriptors. Chronological Weaving is used to integrate short- and long-term temporal information within a coherent temporal context, and a budgeted token router is applied to constrain sequence length while preserving informative summaries. Experiments on MIMIC-IV, eICU, and PhysioNet 2012 show that ReTAMamba consistently improves AUPRC over strong baselines, with average relative gains of 7.51%, 7.80%, and 10.15%, respectively. Cohort-level and patient-level analyses on eICU further showed that the learned mean decay for more dynamic signals, such as heart rate and blood pressure, was 24.3% larger than that for relatively static signals, such as laboratory test variables. These findings suggest that effective prediction in irregular clinical time series requires modeling not only what was measured, but also when and how it was observed, including information freshness and observation timeliness.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Direct visualization of surface spin-flip transition in MnBi4Te7

We report direct visualization of spin-flip transition of the surface layer in antiferromagnet MnBi4Te7, a natural superlattice of alternating MnBi2Te4 and Bi2Te3 layers, using cryogenic magnetic force microscopy (MFM). The observation of magnetic contrast across domain walls and step edges confirms that the antiferromagnetic order persists to the surface layers. The magnetic field dependence of the MFM images reveals that the surface magnetic layer undergoes a first-order spin-flip transition at a magnetic field that is lower than the bulk transition, in excellent agreement with a revised Mills' model. Our analysis indicates an enhancement of the order parameter in the surface magnetic layer, implying robust ferromagnetism in the single-layer limit. The direct visualization of surface spin-flip transition not only opens up exploration of surface metamagnetic transitions in layered antiferromagnets, but also provides experimental support for realizing quantized transport in ultra-thin films of MnBi4Te7 and other natural superlattice topological magnets.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Engineering Weyl phases and nonlinear Hall effects in T$_d$-MoTe$_2$

MoTe$_2$ has recently attracted much attention due to the observation of pressure-induced superconductivity, exotic topological phase transitions, and nonlinear quantum effects. However, there has been debate on the intriguing structural phase transitions among various observed phases of MoTe$_2$, and their connection to the underlying topological electronic properties. In this work, by means of density-functional theory (DFT+U) calculations, we investigate the structural phase transition between the polar T$_d$ and nonpolar 1T$'$ phases of MoTe$_2$ in reference to a hypothetical high-symmetry T$_0$ phase that exhibits higher-order topological features. In the T$_d$ phase we obtain a total of 12 Weyl points, which can be created/annihilated, dynamically manipulated, and switched by tuning a polar phonon mode. We also report the existence of a tunable nonlinear Hall effect in T$_d$-MoTe$_2$, and propose the use of this effect as a probe for the detection of polarity orientation in polar (semi)metals. By studying the role of dimensionality, we identify a configuration in which a nonlinear surface response current emerges. The potential technological applications of the tunable Weyl phase and the nonlinear Hall effect are discussed.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Robust A-type order and spin-flop transition on the surface of the antiferromagnetic topological insulator MnBi$_2$Te$_4$

Here we present microscopic evidence of the persistence of uniaxial A-type antiferromagnetic order to the surface layers of MnBi$_2$Te$_4$ single crystals using magnetic force microscopy. Our results reveal termination-dependent magnetic contrast across both surface step edges and domain walls, which can be screened by thin layers of soft magnetism. The robust surface A-type order is further corroborated by the observation of termination-dependent surface spin-flop transitions, which have been theoretically proposed decades ago. Our results not only provide key ingredients for understanding the electronic properties of the antiferromagnetic topological insulator MnBi$_2$Te$_4$, but also open a new paradigm for exploring intrinsic surface metamagnetic transitions in natural antiferromagnets.

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

Revealing the Hidden Structural Phases of FeRh

${\it Ab}$ ${\it initio}$ electronic structure calculations reveal that tetragonal distortion has a dramatic effect on the relative stability of the various magnetic structures (C-, A-, G-, A$'$-AFM, and FM) of FeRh giving rise to a wide range of novel stable/metastable structures and magnetic phase transitions between these states. We predict that the ${\it cubic}$ G-AFM structure, which was believed thus far to be the ground state, is metastable and that the ${\it tetragonally}$ expanded G-AFM is the stable structure. The low energy barrier separating these states suggests phase coexistence at room temperature. We propose a novel A$'$-AFM phase to be the ${\it global}$ ground state among all magnetic phases which arises from the strain-induced tuning of the exchange interactions. The results elucidate the underlying mechanism for the recent experimental findings of electric-field control of magnetic phase transition driven via tetragonal strain. The novel magnetic phase transitions open interesting prospects for exploiting strain engineering for the next-generation memory devices.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

GdN thin-film: Chern Insulating State on Square Lattice

Using first-principles calculations, we predict a Chern insulating phase in thin films of the ferromagnetic semi-metal GdN. In contrast to previously proposed Chern insulator candidates, which mostly rely on honeycomb lattices, this system affords a great chance to realize the quantum anomalous Hall Effect on a square lattice without either a magnetic substrate or transition metal doping, making synthesis easier. The band inversion between 5d-orbitals of Gd and 2p-orbitals of N is verified by first-principles calculation based on density functional theory, and the band gap can be as large as 100 meV within GdN trilayer. With further increase of film thickness, the band gap tends to close and the metallic bulk property becomes obvious.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Two dimensional topological insulators with tunable band gaps: HgTe and HgSe monolayers

Employing ab initio electronic calculations, we propose a new type of two-dimensional (2D) topological insulator (TI), monolayer (ML) low buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gaps. Monolayer LB HgTe undergoes a transition to a topological nontrivial phase under the appropriate in-plane tensile strain (ε > 2.6%) due to the combination effects of strain and spin orbital coupling (SOC). Under the 2.6%< ε <4.2% tensile strain, the band inversion and topological nontrivial gap are induced by the SOC. For ε >4.2%, the band inversion is already realized by strain but the topological gap is induced by SOC. The band gap of monolayer LB HgTe TI phase can be tuned over a wide range from 0 eV to 0.20 eV as the tensile strain increases from 2.6% to 7.4%. Similarly, the topological phase transition of monolayer LB HgSe is induced by strain and SOC as the strain ε >3.1%. The topological band gap can be 0.05 eV as the strain increases to about 4.6%. The large band gap of 2D LB HgTe and HgSe monolayers make this type of material suitable for practical applications at room-temperature.

0 citations0 reviewsNo code linkedOpen access
preprint2013arXiv

Phonon-induced topological insulating phases in group IV-VI semiconductors

Development of topological insulating phases in IV-VI compounds under dynamic lattice deformations is studied using first-principles methods. Unlike the static state of topological phases at equilibrium conditions, we show that non-trivial topological phases are induced in the compounds by the dynamic lattice deformations from selective phonon modes. Calculations of the time-reversal polarization show that the Z2 invariant of the compounds is flipped by the atomic displacements of selective phonon modes and that the compounds exhibit oscillating topological phases upon dynamic lattice deformations. Our results indicate that the elementary excitations in solids can trigger topological phases in trivial band insulators.

0 citations0 reviewsNo code linkedOpen access
preprint2012arXiv

Topological phase transition in Dirac fermionic heterostructures

Materials with non-trivial topology in their electronic structures enforce the existence of helical Dirac fermionic surface states. We discovered emergent topological phases in the stacked structures of topological insulator and band insulator layers where the surface Dirac fermions interact to each other with particular helicity ordering. Using first-principles calculations and a model Lagrangian, we explicitly demonstrated that such helicity ordering occurs in real materials of ternary chalcogen compounds and determines their topological insulating phase. Our results reveal the rich collective nature of interacting surface Dirac fermions, and pave the way for utilizing topological phases for technological devices such as non-volatile memories.

0 citations0 reviewsNo code linkedOpen access
preprint2010arXiv

Topological insulating behaviour in conducting property of crystalline Ge-Sb-Te

We report a discovery, through first-principles calculations, that crystalline Ge-Sb-Te (GST) phase-change materials exhibit the topological insulating property. Our calculations show that the materials become topological insulator or develop conducting surface-like interface states depending on the layer stacking sequence. It is shown that the conducting interface states originate from topological insulating Sb2Te3 layers in GSTs and can be crucial to the electronic property of the compounds. These interface states are found to be quite resilient to atomic disorders but sensitive to the uniaxial strains. We presented the mechanisms that destroy the topological insulating order in GSTs and investigated the role of Ge migration that is believed to be responsible for the amorphorization of GSTs.

0 citations0 reviewsNo code linkedOpen access