arXiv subjects

Sang Ho Oh

Publications and source records attributed to Sang Ho Oh.

4 recordsLinked to original sources

arXiv2025

Imaging 3D polarization dynamics via deep learning 4D-STEM

Recent advances in ferroelectrics highlight the role of three-dimensional (3D) polar entities in forming topological polar textures and generating giant electromechanical responses, during polarization rotation. However, current electron microscopy methods lack the depth resolution to resolve the polarization component along the electron beam direction, which restricts full characterization. Here, we present a deep learning framework combined with four-dimensional scanning transmission electron microscopy to reconstruct 3D polarization maps in Ba0.5Sr0.5TiO3 thin-film capacitors with picometer-level accuracy under applied electric fields. Our approach enables observation of polar nanodomains consistent with the polar slush model and shows that switching occurs through coordinated vector rotation toward <111> energy minima, rather than magnitude changes. Furthermore, regions with higher topological density exhibit smaller polarization variation when the electric field changes, indicating topological protection. Our work reveals the value of 3D polarization mapping in elucidating complex nanoscale polar phenomena, with broad implications for emergent ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2023

Electronic-grade epitaxial (111) KTaO3 heterostructures

KTaO3 has recently attracted attention as a model system to study the interplay of quantum paraelectricity, spin-orbit coupling, and superconductivity. However, the high and low vapor pressures of potassium and tantalum present processing challenges to creating interfaces clean enough to reveal the intrinsic quantum properties. Here, we report superconducting heterostructures based on electronic-grade epitaxial (111) KTaO3 thin films. Electrical and structural characterizations reveal that two-dimensional electron gas at the heterointerface between amorphous LaAlO3 and KTaO3 thin film exhibits significantly higher electron mobility, superconducting transition temperature and critical current density than those in bulk single crystal KTaO3-based heterostructures owing to cleaner interface in KTaO3 thin films. Our hybrid approach may enable epitaxial growth of other alkali metal-based oxides that lie beyond the capabilities of conventional methods.

cond-mat.mtrl-sci↗

arXiv2022

The origin of jerky dislocation motion in high-entropy alloys

Dislocations in single-phase concentrated random alloys, including high- entropy alloys (HEAs), repeatedly encounter pinning during glide, resulting in jerky dislocation motion. While solute-dislocation interaction is well understood in conventional alloys, the origin of individual pinning points in concentrated random alloys is a matter of debate. In this work, we investigate the origin of dislocation pinning in the CoCrFeMnNi HEA. In- situ transmission electron microscopy studies reveal wavy dislocation lines and a jagged glide motion under external loading, even though no segregation or clustering is found around Shockley partial dislocations. Atomistic simulations reproduce the jerky dislocation motion and link the repeated pinning to local fluctuations in the Peierls friction. We demonstrate that the density of high local Peierls friction is proportional to the critical stress required for dislocation glide and the dislocation mobility.

cond-mat.mtrl-sci↗

arXiv2021

Oxide two-dimensional electron gas with high mobility at room-temperature

The prospect of 2-dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide-bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high-electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO3-based heterostructures. Here, we report 2DEG formation at the LaScO3/BaSnO3 (LSO/BSO) interface with a room-temperature mobility of 60 cm2/V s at a carrier concentration of 1.7x1013 cm-2. This is an order of magnitude higher mobility at room temperature than achieved in SrTiO3-based 2DEGs. We achieved this by combining a thick BSO buffer layer with an ex-situ high-temperature treatment, which not only reduces the dislocation density but also produces a SnO2-terminated atomically flat surface, followed by the growth of an overlying BSO/LSO interface. Using weak-beam dark field imaging and in-line electron holography technique, we reveal a reduction of the threading dislocation density, and provide direct evidence for the spatial confinement of a 2DEG at the BSO/LSO interface. Our work opens a new pathway to explore the exciting physics of stannate-based 2DEGs at application-relevant temperatures for oxide nanoelectronics.

cond-mat.mtrl-sci↗