Searcharxiv⌕ Search

arXiv subjects

Jongbae Hong

Publications and source records attributed to Jongbae Hong.

36 records · Page 2Linked to original sources
arXiv2007

Nonperturbative Dynamical Theory and A Scheme for Nonequilibrium Transport

We develop a nonperturbative dynamical theory (NDT) that is useful for treating nonequilibrium transport in a system with strong correlation. We apply our NDT to the single-impurity Anderson model in equilibrium to check its reliability by comparing with the results of numerical renormalization group method (NRG). We finally suggest a self-consistent loop to calculate the current in a lead-dot-lead system with Kondo coupling.

cond-mat.str-el↗
arXiv2006

Spontaneously Symmetry-Broken Current in Coupled Nanomechanical Shuttles

We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttles. The oscillation frequencies of two shuttles are mode-locked to integer multiples of the applied voltage frequency $ω$. We show that left/right-symmetric double shuttles may generate direct net current due to bistable motions caused by parametric instability. The symmetry-broken direct current appears near $ω=Ω_{0}/(2j-1)$, ($j=1,2,...$), where $Ω_{0}$ is the dressed resonance frequency of the relative motion of the two shuttles.

cond-mat.mes-hall↗
arXiv2006

Local and nonlocal entanglement for quasiparticle pairs induced by Andreev reflection

We investigate local and nonlocal entanglement of particle pairs induced by direct and crossed Andreev reflections at the interfaces between a superconductor and two normal conductors. It is shown theoretically that both local and nonlocal entanglement can be quantified by concurrence and detected from the violation of a Bell inequality of spin current correlators, which are determined only by normal reflection and Andreev reflection eigenvalues. There exists a one-to-one correspondence between the concurrence and the maximal Bell-CHSH parameter in the tunneling limit.

cond-mat.mes-hall↗
arXiv2005

Current-phase relation of the SNS junction in a superconducting loop

We study the current-phase relation of the superconductor/normal/superconductor (SNS) junction imbedded in a superconducting loop. Considering the current conservation and free energy minimum conditions, we obtain the persistent currents of the normal/superconductor (NS) loop. At finite temperature we can explain the experimentally observed highly non-sinusoidal currents which have maxima near the zero external flux.

cond-mat.supr-con↗
arXiv2004

Coupling of Josephson current qubits using a connecting loop

We propose a coupling scheme for the three-Josephson junction qubits which uses a connecting loop, but not mutual inductance. Present scheme offers the advantages of a large and tunable level splitting in implementing the controlled-NOT (CNOT) operation. We calculate the switching probabilities of the coupled qubits in the CNOT operations and demonstrate that present CNOT gate can meet the criteria for the fault-tolerant quantum computing. We obtain the coupling strength as a function of the coupling energy of the Josephson junction and the length of the connecting loop which varies with selecting two qubits from the scalable design.

cond-mat.mes-hall↗
arXiv2003

Kondo lattice model with a direct exchange interaction between localized moments

We study the Kondo lattice model with a direct antiferromagnetic exchange interaction between localized moments. Ferromagnetically long-range ordered state coexisting with the Kondo screening shows a continuous quantum phase transition to the Kondo singlet state. We obtain the value of the critical point where the magnetizations of the localized moments and the conduction electrons vanish. The magnetization curves yield a universal critical exponent independent of the filling factors and the strength of the interaction between localized moments. It is shown that the direct exchange interaction between localized moments introduces another phase transition from an antiferromagnetic ordering to a ferromagnetic ordering for small Kondo exchange interaction. We also explain the local minimum of the Kondo temperature in recent experiments.

cond-mat↗
arXiv2003

Double-Well Potentials in Current Qubits

The effective potentials of the rf-SQUID and three-Josephson junction loop with a penetrating external magnetic flux are studied. Using the periodic boundary condition for the phase evolution of the wave function of Cooper pairs, we obtain new periodic potentials with cusp barriers in contrast with the usual smooth double-well potential. The tunneling through the cusp barrier becomes dominant for a parameter regime where the self inductance of the superconducting loop and the Josephson coupling energy are large. Calculating the tunneling frequency we see that the cusp potential may offer a more efficient qubit.

cond-mat.supr-con↗
arXiv2003

Dc-Driven Diatomic Frenkel-Kontorova Model

We investigate the resonance steps, spatiotemporal dynamics, and dynamical phase diagrams of the dc-driven diatomic Frenkel-Kontorova model. The complete resonance velocity spectrum is given. The diatomic effects result in each resonant state being characterized by two integer pairs, $(k_1,k_2)$ and $(k_1,k_2^{\prime})$. In the high-velocity region the linear response of the average velocity, $v$, of the chain to the driving force $F$ is often punctuated by subharmonic resonances $(k_1>k_2)$. There are two kinds of nonlinear response regions in the high-velocity region. A new physical interpretation of the mean-field treatment is presented.

cond-mat.mtrl-sci↗
arXiv1999

The Generalized Quantum Statistics

The concept of wavefunction reduction should be introduced to standard quantum mechanics in any physical processes where effective reduction of wavefunction occurs, as well as in the measurement processes. When the overlap is negligible, each particle obey Maxwell-Boltzmann statistics even if the particles are in principle described by totally symmetrized wavefunction [P.R.Holland, The Quantum Theory of Motion, Cambridge Unversity Press, 1993, p293]. We generalize the conjecture. That is, particles obey some generalized statistics that contains the quantum and classical statistics as special cases, where the degree of overlapping determines the statistics that particles should obey among continuous generalized statistics. We present an example consistent with the conjecture.

quant-ph↗
arXiv1999

Power-Laws in Nonlinear Granular Chain under Gravity

The signal generated by a weak impulse propagates in an oscillatory way and dispersively in a gravitationally compacted granular chain. For the power-law type contact force, we show analytically that the type of dispersion follows power-laws in depth. The power-law for grain displacement signal is given by $h^{-1/4(1-1/p)}$ where $h$ and $p$ denote depth and the exponent of contact force, and the power-law for the grain velocity is $h^{-1/4({1/3}+1/p)}$. Other depth-dependent power-laws for oscillation frequency, wavelength, and period are given by combining above two and the phase velocity power-law $h^{1/2(1-1/p)}$. We verify above power-laws by comparing with the data obtained by numerical simulations.

cond-mat.stat-mech↗
arXiv1998

Power-Law Behaviors in Nonlinearly Coupled Granular Chain under Gravity

We find power-law behaviors of grain velocity in both propagation and backscattering in a gravitationally compacted granular chain with nonlinear contact force. We focus on the leading peak of the velocity signal which decreases in a power-law $d^{-α}$, where $d$ is the location of the peak, as the signal goes down. The ratio of backscattered to incident leading velocity also follows a power-law $d_i^{-β}$, where $d_i$ is the depth of impurity. The up-going backscattered signal is nearly solitary. Therefore, the overall change of the leading velocity peak is given by the power-law $d_i^{-(α+β)}$. We find $α=0.250$ and $β=0.167$ for the Hertzian contact force.

patt-sol↗
arXiv1997

A Nonperturbative Approach to One-Particle Green's Function

A nonperturbative method to obtain on- and off-site one-particle Green's function is introduced and applied to noninteracting Hubbard model with next nearest neighbor hopping and interacting Hubbard model in large dimensions, for example. The former gives some lessons on the method and shows the advantage of the method compared with continued fraction formalism. The latter is treated by selecting important dynamic processes contributing to the Green's function when correlation is strong. We consider the model in the Bethe lattice with large connectivity. The dynamic processes describing on-site spin fluctuation clearly shows metal-insulator transition in the paramagnetic ground state at half filling.

cond-mat.str-el↗
arXiv1997

Hybridization effect in the Falicov-Kimball model

The extended Falicov-Kimball model which contains hybridization between localized level and conduction band has been studied using the exact diagonalization method. We obtain the single-particle density of states and the valency from this method and analyze the behaviors of valence transition and activation gap. We find that the valence transition is continuous due to hybridization, while the activation gap closes discontinuously. Moreover, the onset of the valence transition and the closing point of the activation gap mismatch each other. Our result is well consistent with the recent experiment on SmB_6.

cond-mat.str-el↗
arXiv1996

Temperature and Pressure Effects on the Resistivity of the Manganese Oxides

The temperature and pressure effects on the resistivity of the manganese oxides are studied analytically via the Kondo lattice model with a strong Hund's coupling. We obtain analytically the single-particle density of states on the Bethe lattice in the large connectivity limit using the analytical variant of the dynamic Lanczos method. From the density of states for the doped system, we obtain resistivity and show resistivity drop when temperature crosses the magnetic transition point. We also demonstrate the effect of pressure both below and above the transition temperature.

cond-mat↗
arXiv1995

Strong correlation effects in the doped Hubbard model in infinite dimensions

The density of states and the optical conductivity of the doped Hubbard model on a Bethe lattice with infinite connectivities have been studied using an analytic variant of the Lanczos continued fraction method. The spectral weight of the gap states and the position of the chemical potential upon hole or electron doping have been studied. We argue that the strong correlation effects such as gap states and midinfrared band shown in two dimensions also appear in infinite dimensions.

cond-mat↗
arXiv1995

Quantitative Description of $V_2O_3$ by the Hubbard Model in Infinite Dimensions

We show that the analytic single-particle density of states and the optical conductivity for the half-filled Hubbard model on the Bethe lattice in infinite dimensions describe quantitatively the behavior of the gap and the kinetic energy ratio of the correlated insulator $V_2O_3$. The form of the optical conductivity shows $ω^{3/2}$ rising and is quite similar to the experimental data, and the density of states shows $ω^{1/2}$ behavior near the band edges.

cond-mat↗
arXiv1995

Analytic Treatment of Mott-Hubbard Transition in the Half-Filled Hubbard Model

The Mott-Hubbard transition in the half-filled Hubbard model is studied analytically for the paramagnetic ground state and the classical Néel state. The single-particle density of states is obtained by calculating the Green's function represented by the infinite continued fraction. The paramagnetic solution shows that the Mott-Hubbard transition is signaled by both collapsing Hubbard bands and appearing $δ$-function peak at midgap, and the transition is second order at the ground state. We also provide specific heats in metallic regime to demonstrate that our results recover those of infinite dimension.

cond-mat↗