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Ju-Hyun Jung

Publications and source records attributed to Ju-Hyun Jung.

10 recordsLinked to original sources
arXiv2025

Wafer-scale Programmed Assembly of One-atom-thick Crystals

Crystalline films offer various physical properties based on the modulation of their thicknesses and atomic structures. The layer-by-layer assembly of atomically thin crystals provides powerful means to arbitrarily design films at the atomic-level, which are unattainable with existing growth technologies. However, atomically-clean assembly of the materials with high scalability and reproducibility remains challenging. We report programmed crystal assembly (PCA) of graphene and monolayer hexagonal boron nitride (ML hBN), assisted by van der Waals interactions, to form wafer-scale films of pristine interfaces with near-unity yield. The atomic configurations of the films are tailored with layer-resolved compositions and in-plane crystalline orientations. We demonstrate batch-fabricated tunnel device arrays with modulation of the resistance over orders of magnitude by thickness-control of the hBN barrier with single-atom precision, and large-scale, twisted multilayer graphene with programmable electronic band structures and crystal symmetries. Our results constitute an important development in the artificial design of large-scale films.

cond-mat.mtrl-sci↗
arXiv2025

Step-directed Epitaxy of Uni-directional Hexagonal Boron Nitride on Vicinal Ge(110)

Insulating hexagonal boron nitride (hBN) films with precisely controlled thickness are ideal dielectric components to modulate various interfaces in electronic devices. To achieve this, high-quality hBN with controlled atomic configurations must be able to form pristine interfaces with various materials in devices. However, previously reported large-scale hBN films with uniform thickness either are polycrystalline or are not suitable for atomically clean assembly via mechanical exfoliation, limiting their applications in device technology. Here, we report the large-scale growth of monolayer single crystalline hBN films on Ge(110) substrates by using chemical vapor deposition (CVD). Vicinal Ge(110) substrates are used for the step-directed epitaxial growth of hBN, where Ge atomic steps act as the hBN nucleation sites, guiding the uni-directional alignments of multiple hBN domains. Density functional theory (DFT) calculations reveal that the optimum hydrogen passivations on both hBN edges and Ge surfaces enable the epitaxial coupling between hBN and the Ge step edges and the single crystallinity of the final hBN films. Using epitaxially grown monolayer hBN films, we fabricate a few hBN films with controlled stacking orders and pristine interfaces through a layer-by-layer assembly process. These films function as high-quality dielectrics to enhance carrier transport in graphene and MoS 2 channels.

cond-mat.mtrl-sci↗
arXiv2018

Pion-cloud contribution to the $N\rightarrow Δ$ transition form factors

We examine the contribution of the pion cloud to the electromagnetic $N \rightarrow Δ$ transition form factors within a relativistic hybrid constituent-quark model. In this model baryons consist not only of the $3q$ valence component, but contain, in addition, a $3 q π$ non-valence component. We start with constituent quarks which are subject to a scalar, isoscalar confining force. This leads to an $SU(6)$ spin-flavor symmetric spectrum with degenerate nucleon and Delta masses. Mass splitting is caused by pions which are assumed to couple directly to the quarks. The point-form of relativistic quantum mechanics is employed to achieve a relativistically invariant description of this system. The $N \rightarrow Δ$ transition current is then determined from the one-photon exchange contribution to the $Δ$ electroproduction amplitude. We will give predictions for the ratios $R_{EM}$ and $R_{SM}$ of electric to magnetic and Coulomb to magnetic form factors, which are supposed to be most sensitive to pion-cloud effects.

hep-ph↗
arXiv2018

Constituent-quark model with pionic contributions: electromagnetic $N\rightarrowΔ$ transition

We report on ongoing work to determine the pion-cloud contribution to the electromagnetic $N\rightarrowΔ$ transition form factors. The starting point is an $SU(6)$ spin-flavor symmetric constituent-quark model with instantaneous confinement that is augmented by dynamical pions which couple directly to the quarks. This system is treated in a relativistically invariant way within the framework of point-form quantum mechanics using a multichannel formulation. The first step is to determine the electromagnetic form factors of the bare particles that consist only of three quarks. These form factors are basic ingredients for calculating the pion-cloud contributions. Already without the pion cloud, electromagnetic nucleon and $N\rightarrow Δ$ transition form factors compare reasonably well with the data. By inclusion of the pion-cloud contribution coming from the $π$-$N$ intermediate state the reproduction of the data is further improved.

nucl-th↗
arXiv2017

On the microscopic structure of $πNN$, $πNΔ$ and $πΔΔ$ vertices

We use a hybrid constituent-quark model for the microscopic description of $πN N$, $πN Δ$ and $πΔΔ$ vertices. In this model quarks are confined by an instantaneous potential and are allowed to emit and absorb a pion, which is also treated as dynamical degree of freedom. The point form of relativistic quantum mechanics is employed to achieve a relativistically invariant description of this system. Starting with an $SU(6)$ spin-flavor symmetric wave function for $N_0$ and $Δ_0$, i.e. the eigenstates of the pure confinement problem, we calculate the strength of the $πN_0 N_0$, $πN_0 Δ_0$ and $πΔ_0 Δ_0$ couplings and the corresponding vertex form factors. Interestingly the ratios of the resulting couplings resemble strongly those needed in purely hadronic coupled-channel models, but deviate significantly from the ratios following from SU(6) spin-flavor symmetry in the non-relativistic constituent-quark model.

nucl-th↗
arXiv2016

The microscopic structure of $πNN$, $πNΔ$ and $πΔΔ$ vertices in a hybrid constituent quark model

We present a microscopic description of the strong $πNN$, $πNΔ$ and $πΔΔ$ vertices. Our starting point is a constituent-quark model supplemented by an additional $3qπ$ non-valence component. In the spirit of chiral constituent-quark models, quarks are allowed to emit and reabsorb a pion. This multichannel system is treated in a relativistically invariant way within the framework of point-form quantum mechanics. Starting with a common $SU(6)$ spin-flavor-symmetric wave function for $N$ and $Δ$, we calculate the strength of the $πNN$, $πNΔ$ and $πΔΔ$ couplings and the corresponding vertex form factors. Our results are in accordance with phenomenological fits of these quantities that have been obtained within purely hadronic multichannel models for baryon resonances.

nucl-th↗
arXiv2015

Modification of generalized vector form factors and transverse charge densities of the nucleon in nuclear matter

We investigate the medium modification of the generalized vector form factors of the nucleon, which include the electromagnetic and energy-momentum tensor form factors, based on an in-medium modified $π$-$ρ$-$ω$ soliton model. We find that the vector form factors of the nucleon in nuclear matter fall off faster than those in free space, which implies that the charge radii of the nucleon become larger in nuclear medium than in free space. We also compute the corresponding transverse charge densities of the nucleon in nuclear matter, which clearly reveal the increasing of the nucleon size in nuclear medium.

hep-ph↗
arXiv2014

Energy-momentum tensor form factors of the nucleon within a $π$-$ρ$-$ω$ soliton model

We investigate the energy-momentum tensor form factors of the nucleon within the famework of a chiral soliton model, including the $ρ$ and $ω$ vector mesons. We examine the role of each meson degrees of freedom in these form factors. It is explicitly shown that the pion provides strong attraction whereas the $ρ$ and $ω$ yield repulsion in such a way that the soliton becomes stabilized. The results are discussed in comparison with those of other models.

hep-ph↗
arXiv2012

In-medium modified $π$-$ρ$-$ω$ mesonic Lagrangian and properties of nuclear matter

We investigate the bulk properties of symmetric nuclear matter within the framework of an in-medium modified chiral solitonic model with $π$, $ρ$ and $ω$ mesons. We consider the modification of meson degrees of freedom in nuclear matter, based on phenomenology of pion-nucleus scattering and the empirical nuclear mass formula. We discuss the results of the density dependence of the volume term in the mass formula and the incompressibility of symmetric nuclear matter, comparing them with relativistic mean-field models. The mass dropping of the $ρ$ meson in nuclear matter is also obtained and discussed.

hep-ph↗