2,994 research outputs found
Critical currents for vortex defect motion in superconducting arrays
We study numerically the motion of vortices in two-dimensional arrays of
resistively shunted Josephson junctions. An extra vortex is created in the
ground states by introducing novel boundary conditions and made mobile by
applying external currents. We then measure critical currents and the
corresponding pinning energy barriers to vortex motion, which in the
unfrustrated case agree well with previous theoretical and experimental
findings. In the fully frustrated case our results also give good agreement
with experimental ones, in sharp contrast with the existing theoretical
prediction. A physical explanation is provided in relation with the vortex
motion observed in simulations.Comment: To appear in Physical Review
Dynamic transition and Shapiro-step melting in a frustrated Josephson-junction array
We consider a two-dimensional fully frustrated Josephson-junction array
driven by combined direct and alternating currents. Interplay between the mode
locking phenomenon, manifested by giant Shapiro steps in the current-voltage
characteristics, and the dynamic phase transition is investigated at finite
temperatures. Melting of Shapiro steps due to thermal fluctuations is shown to
be accompanied by the dynamic phase transition, the universality class of which
is also discussed
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.Comment: 8 pages in two columns, 8 figures, to appear in Phys. Rev.
Counting statistics based on the analytic solutions of the differential-difference equation for birth-death processes
Birth-death processes take place ubiquitously throughout the universe. In
general, birth and death rates depend on the system size (corresponding to the
number of products or customers undergoing the birth-death process) and thus
vary every time birth or death occurs, which makes fluctuations in the rates
inevitable. The differential-difference equation governing the time evolution
of such a birth-death process is well established, but it resists solving for a
non-asymptotic solution. In this work, we present the analytic solution of the
differential-difference equation for birth-death processes without
approximation. The time-dependent solution we obtain leads to an analytical
expression for counting statistics of products (or customers). We further
examine the relationship between the system size fluctuations and the birth and
death rates, and find that statistical properties (variance subtracted by mean)
of the system size are determined by the mean death rate as well as the
covariance of the system size and the net growth rate (i.e., the birth rate
minus the death rate). This work suggests a promising new direction for
quantitative investigations into birth-death processes
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