arXiv subjects

Chang-Mo Ryu

Publications and source records attributed to Chang-Mo Ryu.

11 recordsLinked to original sources

arXiv2022

Density filamentation nonlinearly driven by the Weibel instability in relativistic beam plasmas

Density filamentation has been observed in many beam-plasma simulations and experiments. Because current filamentation is a pure transverse mode, charge density filamentation cannot be produced directly by the current filamentation process. To explain this phenomenon, several mechanisms are proposed such as the coupling of the Weibel instability to the two-stream instability, coupling to the Langmuir wave, differences in thermal velocities between the beam and return currents, the magnetic pressure gradient force, etc. In this paper, it is shown that the gradient of the Lorentz factor can, in fact, represent the nonlinear behavior of a plasma fluid and further that the nonuniform Lorentz factor distribution can give rise to electrostatic fields and density filaments. Simulation results together with theoretical analyses are presented.

physics.plasm-ph↗

arXiv2021

Dynamical Screening Effects on Big Bang Nucleosynthesis

A moving ion in plasma creates a deformed electric potential depending on the ion velocity, which leads to the distinct screening effect compared to the standard static Salpeter formula. In this paper, adopting the test charge method, we explore the dynamical screening effects on big bang nucleosynthesis (BBN). We find that the high temperature in the early universe causes the ion velocity to be faster than the solar condition so that the electric potential is effectively polarized. However, the low density of background plasma components significantly suppresses the dynamical screening effects on thermonuclear reaction rates during the BBN epoch. We compare our results with several thermonuclear reaction rates for solar fusion considering the dynamical screening effects. Also, we discuss the additional plasma properties in other astrophysical sites for the possible expansion from the present calculation in the future.

nucl-th↗

arXiv2021

Turbulence-induced transport dynamo mechanism

The transport dynamo mechanism, which describes the magnetic field generation by diffusion flow is reviewed. In this mechanism, the cross-field transport caused by the random motion of fluid breaks the frozen-flux approximation, and the resulting cross-field diffusion that can generate the magnetic field. Turbulence can play an important role in inducing such random motion. Compared to the conventional dynamo mechanism, this transport mechanism has several special features that the field generation can occur on a very slow time scale because the mechanism is mediated by diffusion and that this mechanism is practically meaningful only when there is density inhomogeneity. Turbulence can significantly enhance cross-field diffusion far beyond collisional transport. The physical meanings of the diffusion-generated magnetic fields are discussed in detail.

physics.flu-dyn↗

arXiv2019

Biermann battery effects on the turbulent dynamo in a colliding plasma jets produced by high-power lasers

The implication of the Biermann battery (BB) on turbulent magnetic field amplification in colliding plasma jets produced by high-power lasers is studied by using the FLASH code. It is found that the BB can play a significant role in turbulent field amplification. The small scale fluid structures introduced by turbulence can allow the BB to effectively amplify the magnetic field. When the flow is perpendicular to the magnetic field, the magnetic field amplification is shown to be greater than the case where the flow is parallel.

physics.plasm-ph↗

arXiv2002

Effects of broken time-reversal symmetry on transmission zeros in the Aharonov-Bohm interferometer

In this paper, we study the behavior of the transmission zeros in the closed Aharonov-Bohm(AB) interferometer with an embedded scattering center in one arm and the corresponding change in the transmission phase when the time-reversal symmetry is broken by magnetic fields. Specifically, we consider three embedded scattering centers: one discrete energy level, a double-barrier well, and a $t$-stub. We find the followings from our model study: (i) The transmission zeros are real when the AB flux is an integer or a half-integer multiple of the flux quantum, and the transmission phase jumps by $π$ at the zeros. (ii) The transmission zeros become complex or are shifted off the real-energy axis when the magnetic AB flux is not an integer or a half-integer multiple of the flux quantum, and the transmission phase evolves continuously. (iii) The distance of the zeros from the real-energy axis or the imaginary part of the transmission zeros is sinusoidal as a function of the magnetic AB phase. We suggest the experimental setup which can test our results.

cond-mat.mes-hall↗

arXiv2001

Ferromagnetic Fixed Point of the Kondo Model in a Luttinger Liquid

The Kondo effect in a Luttinger liquid is studied using the renormalization group method. By renormalizing the boson fields, scaling equations to the second order for an arbitrary Luttinger interaction are obtained. For the ferromagnetic Kondo coupling, a spin bound state(triplet) can be realized without invoking a nearest neighbor spin interaction in agreement with the recent Bethe ansatz calculation. The scaling theory in the presence of the scalar potential shows that there is no interplay between the magnetic and non-magnetic interaction. Also a study on the crossover behavior of the Kondo temperature between the exponential and the power law type is presented.

cond-mat.str-el↗

arXiv2000

Spin Fluctuation and Persistent Current in a Mesoscopic Ring Coupled to a Quantum Dot

We investigate the persistent current influenced by the spin fluctuations in a mesoscopic ring weakly coupled to a quantum dot. It is shown that the Kondo effect gives rise to some unusual features of the persistent current in the limit where the charge transfer between two subsystems is suppressed. Various aspects of the crossover from a delocalized to a localized dot limit are discussed in relation with the effect of the coherent response of the Kondo cloud to the Aharonov-Bohm flux.

cond-mat.mes-hall↗

arXiv1999

Photon-Assisted Quasiparticle Transport and Andreev Transport through an Interacting Quantum Dot

Resonant tunneling through a quantum dot coupled to superconducting reservoirs in the presence of time-dependent external voltage has been studied. A general formula of the current is derived based on the nonequilibrium Green's function technique. Using this formula photon-assisted quasiparticle transport has been investigated for the quantum dot connected to superconductors. In addition, resonant Andreev transport through a strongly correlated quantum dot connected to a normal metallic lead and a superconducting lead is studied.

cond-mat.mes-hall↗

arXiv1998

Circulating and persistent currents induced by a current magnification and Aharonov-Casher phase

We considered the circulating current induced by the current magnification and the persistent current induced by Aharonov-Casher flux. The persistent currents have directional dependence on the direct current flow, but the circulating currents have no directional dependence. Hence in the equilibrium, only the persistent current can survives on the ring. For the charge current, the persistent charge current cancelled between spin up and down states, because of the time reversal symmetry of the Hamiltonian on the ring. So there are only circulating charge currents on the ring for electrons with unpolarized spin in the nonequilibrium. However, only the persistent spin currents contributes to the spin currents for electrons with unpolarized spin.

cond-mat.mes-hall↗

arXiv1998

Multi-anyons in the magnetic field

We consider the external magnetic field effects on the two types of anyon with fractional statistical parameters $p/q$ with coprimes $p$ and $q$, one with fractional charge $e/q $ and flux $p ϕ_0(=hc/e)$(type I), the other with fractional flux $p ϕ_0/q$ and fundamental charge $e$(type II). These two-types of anyons show different behaviors in the presence of the external magnetic field. We also considered the geometry in which a two-dimensional plane contains an island of anyons with different statistical parameter in their equilibrium. The equilibrium inside an island is shown to be periodic with respect to the flux through the island. The period for the type I anyon equals to the integer multiple of the fundamental flux quantum. In the case of type II anyon the period is found to be the fractional multiple of the fundamental flux quantum.

cond-mat.mes-hall↗

arXiv1998

Directional dependence of spin currents induced by Aharonov-Casher phase

We have calculated the persistent spin current of an open ring induced by the Aharonov-Casher phase. For unpolarized electrons there exist no persistent charge currents, but persistent spin currents. We show that, in general, the magnitude of the persistent spin current in a ring depends on the direction of the direct current flow from one reservoir to another. The persistent spin current is modulated by the cosine function of the spin precession angle. The nonadiabatic Aharonov-Casher phase gives anomalous behaviors. The Aharonov-Anandan phase is determined by the solid angle of spin precession. When the nonadiabatic Aharonov-Anandan phase approaches a constant value with the increase of the electric field, the periodic behavior of the spin persistent current occurs in an adiabatic limit. In this limit the periodic behavior of the persistent spin current could be understood by the effective spin-dependent Aharonov-Bohm flux.

cond-mat.mes-hall↗