arXiv subjects

Gun Sang Jeon

Publications and source records attributed to Gun Sang Jeon.

45 records · Page 3Linked to original sources

arXiv2002

Dynamic transitions and resonances in Josephson-junction arrays under oscillating magnetic fields

We investigate dynamic transitions and stochastic resonance phenomena in two-dimensional fully frustrated Josephson-junction arrays driven by staggered oscillating magnetic fields. As the temperature is lowered, the dynamic order parameter, defined to be the average staggered magnetization, is observed to acquire nonzero values. The resulting transition is found to belong to the same universality as the equilibrium Z_2 transition for small driving amplitudes while large driving fields appear to induce deviation from the universality class. The transition is also manifested by the stochastic resonance peak of the signal-to-noise ratio, which develops above the transition temperature.

cond-mat↗

arXiv2001

Spontaneous phase oscillation induced by inertia and time delay

We consider a system of coupled oscillators with finite inertia and time-delayed interaction, and investigate the interplay between inertia and delay both analytically and numerically. The phase velocity of the system is examined; revealed in numerical simulations is emergence of spontaneous phase oscillation without external driving, which turns out to be in good agreement with analytical results derived in the strong-coupling limit. Such self-oscillation is found to suppress synchronization and its frequency is observed to decrease with inertia and delay. We obtain the phase diagram, which displays oscillatory and stationary phases in the appropriate regions of the parameters.

cond-mat.stat-mech↗

arXiv2001

XY model in small-world networks

The phase transition in the XY model on one-dimensional small-world networks is investigated by means of Monte-Carlo simulations. It is found that long-range order is present at finite temperatures, even for very small values of the rewiring probability, suggesting a finite-temperature transition for any nonzero rewiring probability. Nature of the phase transition is discussed in comparison with the globally-coupled XY model.

cond-mat.stat-mech↗

arXiv2001

Double stochastic resonance peaks in systems with dynamic phase transitions

To probe the connection between the dynamic phase transition and stochastic resonance, we study the mean-field kinetic Ising model and the two-dimensional Josephson-junction array in the presence of appropriate oscillating magnetic fields. Observed in both systems are {\it double} stochastic resonance peaks, one below and the other above the dynamic transition temperature, the appearance of which is argued to be a generic property of the system with a continuous dynamic phase transition. In particular, the frequency matching condition around the dynamic phase transition between the external drive frequency and the internal characteristic frequency of the system is identified as the origin of such double peaks.

cond-mat.stat-mech↗

arXiv2000

Spatiotemporal Stochastic Resonance in Fully Frustrated Josephson Ladders

We consider a Josephson-junction ladder in an external magnetic field with half flux quantum per plaquette. When driven by external currents, periodic in time and staggered in space, such a fully frustrated system is found to display spatiotemporal stochastic resonance under the influence of thermal noise. Such resonance behavior is investigated both numerically and analytically, which reveals significant effects of anisotropy and yields rich physics.

cond-mat.supr-con↗

arXiv2000

Intrinsic finite-size effects in the two-dimensional XY model with irrational frustration

This study investigates in detail the finite-size scaling of the two-dimensional irrationally frustrated XY model. By means of Monte Carlo simulations with entropic sampling, we examine the size dependence of the specific heat, and find remarkable deviation from the conventional finite-size scaling theory, which reveals novel intrinsic finite-size effects. Relaxation dynamics of the system is also considered, and correspondingly, finite-size scaling of the relaxation time is examined, again giving evidence for the intrinsic finite-size effects and suggesting a zero-temperature glass transition.

cond-mat↗

arXiv2000

Boundary Effects on Dynamic Behavior of Josephson-Junction Arrays

The boundary effects on the current-voltage characteristics in two-dimensional arrays of resistively shunted Josephson junctions are examined. In particular, we consider both the conventional boundary conditions (CBC) and the fluctuating twist boundary conditions (FTBC), and make comparison of the obtained results. It is observed that the CBC, which have been widely adopted in existing simulations, may give a problem in scaling, arising from rather large boundary effects; the FTBC in general turn out to be effective in reducing the finite-size effects, yielding results with good scaling behavior. To resolve the discrepancy between the two boundary conditions, we propose that the proper scaling in the CBC should be performed with the boundary data discarded: This is shown to give results which indeed scale well and are the same as those from the FTBC.

cond-mat.supr-con↗

arXiv1998

Quantum phase transitions in superconducting arrays under external magnetic fields

We study the zero-temperature phase transitions of two-dimensional superconducting arrays with both the self- and the junction capacitances in the presence of external magnetic fields. We consider two kinds of excitations from the Mott insulating phase: charge-dipole excitations and single-charge excitations, and apply the second-order perturbation theory to find their energies. The resulting phase boundaries are found to depend strongly on the magnetic frustration, which measures the commensurate-incommensurate effects. Comparison of the obtained values with those in recent experiment suggests the possibility that the superconductor-insulator transition observed in experiment may not be of the Berezinskii-Kosterlitz-Thouless type. The system is also transformed to a classical three-dimensional XY model with the magnetic field in the time-direction; this allows the analogy to bulk superconductors, revealing the nature of the phase transitions.

cond-mat.supr-con↗

arXiv1996

Coulomb Gaps in One-Dimensional Spin-Polarized Electron Systems

We investigate the density of states (DOS) near the Fermi energy of one-dimensional spin-polarized electron systems in the quantum regime where the localization length is comparable to or larger than the inter-particle distance. The Wigner lattice gap of such a system, in the presence of weak disorder, can occur precisely at the Fermi energy, coinciding with the Coulomb gap in position. The interplay between the two is investigated by treating the long-range Coulomb interaction and the random disorder potential in a self-consistent Hartree-Fock approximation. The DOS near the Fermi energy is found to be well described by a power law whose exponent decreases with increasing disorder strength.

cond-mat↗