arXiv subjects

Sung Joo Kim

Publications and source records attributed to Sung Joo Kim.

3 recordsLinked to original sources

arXiv2026

Achieving 5-angstrom-resolution diffraction contrast with an uncorrected electron probe and nanosized defect characterizations

Atomic-resolution micrographs remain limited in application due to small field of view and low numbers of recorded defects. Defect imaging with reliable statistics in transmission electron microscopy (TEM) relies heavily on diffraction contrast. However, with 200-300 kV electrons, low-curvature Ewald sphere limits diffraction resolution at ~5 nm. Here, we imaged defects with a forbidden condition in TEM and improved the resolution in diffraction contrast from 5 to 0.5 nm. The superiority of our equal-s method is demonstrated by the discovery of a novel phase and dislocation loop structure in steels, which have not been previously reported experimentally or theoretically. Our equal-s can largely replace the classical two-beam condition for defect study.

cond-mat.mtrl-sci↗

arXiv2026

Collective AI can amplify tiny perturbations into divergent decisions

Large language models are increasingly deployed not as single assistants but as committees whose members deliberate and then vote or synthesize a decision. Such systems are often expected to be more robust than individual models. We show that iterative multi-LLM deliberation can instead amplify tiny perturbations into divergent conversational trajectories and different final decisions. In a fully deterministic self-hosted benchmark, exact reruns are identical, yet small meaning-preserving changes to the scenario text still separate over time and often alter the final recommendation. In deployed black-box API systems, nominally identical committee runs likewise remain unstable even at temperature 0, where many users expect near-determinism. Across 12 policy scenarios, these findings indicate that instability in collective AI is not only a consequence of residual platform-side stochasticity, but can arise from sensitivity to nearby initial conditions under repeated interaction itself. Additional deployed experiments show that committee architecture modulates this instability: role structure, model composition, and feedback memory can each alter the degree of divergence. Collective AI therefore faces a stability problem, not only an accuracy problem: deterministic execution alone does not guarantee predictable or auditable deliberative outcomes.

cs.AI↗

arXiv2011

Experimental Evidence of Ferroelectric Negative Capacitance in Nanoscale Heterostructures

We report a proof-of-concept demonstration of negative capacitance effect in a nanoscale ferroelectric-dielectric heterostructure. In a bilayer of ferroelectric, Pb(Zr0.2Ti0.8)O3 and dielectric, SrTiO3, the composite capacitance was observed to be larger than the constituent SrTiO3 capacitance, indicating an effective negative capacitance of the constituent Pb(Zr0.2Ti0.8)O3 layer. Temperature is shown to be an effective tuning parameter for the ferroelectric negative capacitance and the degree of capacitance enhancement in the heterostructure. Landau's mean field theory based calculations show qualitative agreement with observed effects. This work underpins the possibility that by replacing gate oxides by ferroelectrics in MOSFETs, the sub threshold slope can be lowered below the classical limit (60 mV/decade).

cond-mat.mes-hall↗