Showing 1–8 of 8 results for author: Kim, J U

Order-Disorder Tricriticality in $\mathrm{A}_n \mathrm{B}_n$ Star Polymer Melts

Authors: Minhoon Kim, Wonjun Kang, Daeseong Yong, Junhan Cho, Jaeup U. Kim

Abstract: Tricriticality usually requires tuning an additional thermodynamic parameter. Here we show that, in symmetric $\mathrm{A}_n\mathrm{B}_n$ star-polymer melts, the arm number $n$ itself plays this role and drives the order--disorder transition (ODT) from second order to first order. By developing a sixth-order free-energy expansion within the random phase approximation and comparing it with self-cons… ▽ More Tricriticality usually requires tuning an additional thermodynamic parameter. Here we show that, in symmetric $\mathrm{A}_n\mathrm{B}_n$ star-polymer melts, the arm number $n$ itself plays this role and drives the order--disorder transition (ODT) from second order to first order. By developing a sixth-order free-energy expansion within the random phase approximation and comparing it with self-consistent field theory (SCFT) calculations, we analytically identify a tricritical arm number, $n_{\mathrm{tc}}\approx 5.4475$. For $n<n_{\mathrm{tc}}$, the lamellar ordering transition remains continuous and occurs at the spinodal point, $(χN)_{\mathrm{s}}\approx 10.495$. For $n>n_{\mathrm{tc}}$, the transition becomes first order, and $(χN)_{\mathrm{ODT}}$ shifts below $(χN)_{\mathrm{s}}$ with a quadratic dependence near the tricritical point. SCFT calculations confirm the predicted transition character and phase-boundary shift. The origin of this behavior is traced to inter-arm correlations generated by the common junction. We further show that the noninteger tricritical arm number can be effectively realized in binary mixtures of star polymers. This provides a rare analytically tractable example of architecture-induced tricriticality in a microphase-separating polymer system. △ Less

Submitted 22 May, 2026; originally announced May 2026.

Motile bacteria crossing liquid-liquid interfaces

Authors: Jiyong Cheon, Joowang Son, Sungbin Lim, Yundon Jeong, Jung-Hoon Park, Robert J. Mitchell, Jaeup U. Kim, Joonwoo Jeong

Abstract: Real-life bacteria often swim in complex fluids, but our understanding of the interactions between bacteria and complex surroundings is still evolving. In this work, rod-like \textit{Bacillus subtilis} swims in a quasi-2D environment with aqueous liquid-liquid interfaces, i.e., the isotropic-nematic coexistence phase of an aqueous chromonic liquid crystal. Focusing on the bacteria motion near and… ▽ More Real-life bacteria often swim in complex fluids, but our understanding of the interactions between bacteria and complex surroundings is still evolving. In this work, rod-like \textit{Bacillus subtilis} swims in a quasi-2D environment with aqueous liquid-liquid interfaces, i.e., the isotropic-nematic coexistence phase of an aqueous chromonic liquid crystal. Focusing on the bacteria motion near and at the liquid-liquid interfaces, we collect and quantify bacterial trajectories ranging across the isotropic to the nematic phase. Despite its small magnitude, the interfacial tension of the order of 10 $\mathrm{μN/m}$ at the isotropic-nematic interface justifies our observations that bacteria swimming more perpendicular to the interface have a higher probability of crossing the interface. Our force-balance model, considering the interfacial tension, further predicts how the length and speed of the bacteria affect their crossing behaviors. We also find, as soon as the bacteria cross the interface and enter the nematic phase, they wiggle less, but faster, and that this occurs as the flagellar bundles aggregate within the nematic phase. △ Less

Submitted 12 April, 2024; v1 submitted 7 February, 2024; originally announced February 2024.

Revival of electron coherence in a finite-length quantum wire

Authors: Jaeuk U. Kim, W. -R. Lee, Hyun-Woo Lee, H. -S. Sim

Abstract: We study the spatial decay of electron coherence due to electron-electron interaction in a finite-length disorder-free quantum wire. Based on the Luttinger liquid theory, we demonstrate that the coherence length characterizing the exponential decay of the coherence can vary from region to region, and that the coherence can even revive after the decay. This counterintuitive behavior, which is in… ▽ More We study the spatial decay of electron coherence due to electron-electron interaction in a finite-length disorder-free quantum wire. Based on the Luttinger liquid theory, we demonstrate that the coherence length characterizing the exponential decay of the coherence can vary from region to region, and that the coherence can even revive after the decay. This counterintuitive behavior, which is in clear contrast to the conventional exponential decay with single coherence length, is due to the fractionalization of an electron and the finite-size-induced recombination of the fractions. △ Less

Submitted 17 January, 2009; originally announced January 2009.

Comments: 4+ pages, 3 figures, to appear in Physical Review Letters

Fano resonance in a two-level quantum dot side-coupled to leads

Authors: W. -R. Lee, Jaeuk U. Kim, H. -S. Sim

Abstract: We theoretically study Fano resonance in a two-level quantum dot side-coupled to two leads, which are connected by a direct channel. The resonance lineshape is found to be deformed, from the conventional Fano form, by interlevel Coulomb interaction and interlevel interference. We derive the connection between the lineshape deformation and the interaction-induced nonmonotonicity of level occupati… ▽ More We theoretically study Fano resonance in a two-level quantum dot side-coupled to two leads, which are connected by a direct channel. The resonance lineshape is found to be deformed, from the conventional Fano form, by interlevel Coulomb interaction and interlevel interference. We derive the connection between the lineshape deformation and the interaction-induced nonmonotonicity of level occupation, which may be useful for experimental study. The dependence of the lineshape on the transmission of the direct channel and on the dot-lead coupling matrix elements is discussed. △ Less

Submitted 16 October, 2007; originally announced October 2007.

Comments: 4 pages, 4 figures

Journal ref: Physical Review B 77, 033305 (2008)

Nonequilibrium plasmons and transport properties of a double--junction quantum wire

Authors: Jaeuk U. Kim, Mahn-Soo Choi, Ilya V. Krive, Jari M. Kinaret

Abstract: We study theoretically the current-voltage characteristics, shot noise, and full counting statistics of a quantum wire double barrier structure. We model each wire segment by a spinless Luttinger liquid. Within the sequential tunneling approach, we describe the system's dynamics using a master equation. We show that at finite bias the non-equilibrium distribution of plasmons in the central wire… ▽ More We study theoretically the current-voltage characteristics, shot noise, and full counting statistics of a quantum wire double barrier structure. We model each wire segment by a spinless Luttinger liquid. Within the sequential tunneling approach, we describe the system's dynamics using a master equation. We show that at finite bias the non-equilibrium distribution of plasmons in the central wire segment leads to increased average current, enhanced shot noise, and full counting statistics corresponding to a super-Poissonian process. These effects are particularly pronounced in the strong interaction regime, while in the non-interacting case we recover results obtained earlier using detailed balance arguments. △ Less

Submitted 16 March, 2005; originally announced March 2005.

Comments: 22 pages, RevTex 2-column, 11 figures

Shot Noise and Full Counting Statistics from Non-equilibrium Plasmons in Luttinger-Liquid Junctions

Authors: Jaeuk U. Kim, Jari M. Kinaret, Mahn-Soo Choi

Abstract: We consider a quantum wire double junction system with each wire segment described by a spinless Luttinger model, and study theoretically shot noise in this system in the sequential tunneling regime. We find that the non-equilibrium plasmonic excitations in the central wire segment give rise to qualitatively different behavior compared to the case with equilibrium plasmons. In particular, shot n… ▽ More We consider a quantum wire double junction system with each wire segment described by a spinless Luttinger model, and study theoretically shot noise in this system in the sequential tunneling regime. We find that the non-equilibrium plasmonic excitations in the central wire segment give rise to qualitatively different behavior compared to the case with equilibrium plasmons. In particular, shot noise is greatly enhanced by them, and exceeds the Poisson limit. We show that the enhancement can be explained by the emergence of several current-carrying processes, and that the effect disappears if the channels effectively collapse to one due to, {\em e.g.}, fast plasmon relaxation processes. △ Less

Submitted 17 March, 2005; v1 submitted 24 March, 2004; originally announced March 2004.

Comments: 9 pages; IOP Journal style; several changes in the text

Journal ref: J. Phys.: Condens. Matt. 17, 3815 (2005)

Non-equilibrium Plasmons in a Quantum Wire Single Electron Transistor

Authors: Jaeuk U. Kim, Ilya V. Krive, Jari M. Kinaret

Abstract: We analyze a single electron transistor composed of two semi-infinite one dimensional quantum wires and a relatively short segment between them. We describe each wire section by a Luttinger model, and treat tunneling events in the sequential approximation when the system's dynamics can be described by a master equation. We show that the steady state occupation probabilities in the strongly inter… ▽ More We analyze a single electron transistor composed of two semi-infinite one dimensional quantum wires and a relatively short segment between them. We describe each wire section by a Luttinger model, and treat tunneling events in the sequential approximation when the system's dynamics can be described by a master equation. We show that the steady state occupation probabilities in the strongly interacting regime depend only on the energies of the states and follow a universal form that depends on the source-drain voltage and the interaction strength. △ Less

Submitted 31 March, 2003; v1 submitted 3 February, 2003; originally announced February 2003.

Comments: 4 pages, 3 figures. To appear in the Phys. Rev. Lett

Journal ref: Phys. Rev. Lett. 90, 176401 (2003)

Morphology Selection of Nanoparticle Dispersions by Polymer Media

Authors: Jaeup U. Kim, Ben O'Shaughnessy

Abstract: Designable media can control properties of nanocomposite materials by spatially organizing nanoparticles. Here we theoretically study particle organization by ultrathin polymer films of grafted chains (``brushes''). Polymer-soluble nanoparticles smaller than a brush-determined threshold disperse in the film to a depth scaling inversely with particle volume. In the polymer-insoluble case, aggrega… ▽ More Designable media can control properties of nanocomposite materials by spatially organizing nanoparticles. Here we theoretically study particle organization by ultrathin polymer films of grafted chains (``brushes''). Polymer-soluble nanoparticles smaller than a brush-determined threshold disperse in the film to a depth scaling inversely with particle volume. In the polymer-insoluble case, aggregation is directed: provided particles are non-wetting at the film surface, the brush stabilizes the dispersion and selects its final morphology of giant elongated aggregates with a brush-selected width. △ Less

Submitted 1 February, 2002; originally announced February 2002.

Comments: 8 pages, 4 figures, submitted to Phys. Rev. Lett