69 research outputs found
Bunching of fluxons by the Cherenkov radiation in Josephson multilayers
A single magnetic fluxon moving at a high velocity in a Josephson multilayer
(e.g., high-temperature superconductor such as BSCCO) can emit electromagnetic
waves (Cherenkov radiation), which leads to formation of novel stable dynamic
states consisting of several bunched fluxons. We find such bunched states in
numerical simulation in the simplest cases of two and three coupled junctions.
At a given driving current, several different bunched states are stable and
move at velocities that are higher than corresponding single-fluxon velocity.
These and some of the more complex higher-order bunched states and transitions
between them are investigated in detail.Comment: 6 pages + 6 Figures, to be published in Phys. Rev. B on July 1, 200
Ground states of one and two fractional vortices in long Josephson 0-kappa-junctions
Half integer Josephson vortices in 0--junctions, discussed theoretically
and observed experimentally, spontaneously appear at the point where the
Josephson phase is -discontinuous. The creation of \emph{arbitrary}
discontinuities of the Josephson phase has been demonstrated recently. Here we
study fractional vortices formed at an arbitrary -discontinuity,
discuss their stability and possible ground states. The two stable states are
not mirror symmetric. Furthermore, the possible ground states formed at two
-discontinuities separated by a distance are investigated, and the
energy and the regions of stability of each ground state are calculated. We
also show that the ground states may strongly depend on the distance
between the discontinuities. There is a crossover distance such that for
the ground states may be qualitatively different.Comment: 7 figures, submitted to PRB In v.2 one figure is added, and refs are
updated In v.3 major revision, many issues fixe
Effective phase description of noise-perturbed and noise-induced oscillations
An effective description of a general class of stochastic phase oscillators
is presented. For this, the effective phase velocity is defined either by
invariant probability density or via first passage times. While the first
approach exhibits correct frequency and distribution density, the second one
yields proper phase resetting curves. Their discrepancy is most pronounced for
noise-induced oscillations and is related to non-monotonicity of the phase
fluctuations
Controllable plasma energy bands in a 1D crystal of fractional Josephson vortices
We consider a 1D chain of fractional vortices in a long Josephson junction
with alternating phase discontinuities. Since each vortex has its
own eigenfrequency, the inter-vortex coupling results in eigenmode splitting
and in the formation of an oscillatory energy band for plasma waves. The band
structure can be controlled at the design time by choosing the distance between
vortices or \emph{during experiment} by varying the topological charge of
vortices or the bias current. Thus one can construct an artificial vortex
crystal with controllable energy bands for plasmons.Comment: 4 pages, 2 Fig
Modeling the burnout of solid polydisperse fuel under the conditions of external heat transfer
Oscillatory eigenmodes and stability of one and two arbitrary fractional vortices in long Josephson 0-kappa-junctions
We investigate theoretically the eigenmodes and the stability of one and two
arbitrary fractional vortices pinned at one and two -phase
discontinuities in a long Josephson junction. In the particular case of a
single -discontinuity, a vortex is spontaneously created and pinned at
the boundary between the 0 and -regions. In this work we show that only
two of four possible vortices are stable. A single vortex has an oscillatory
eigenmode with a frequency within the plasma gap. We calculate this
eigenfrequency as a function of the fractional flux carried by a vortex.
For the case of two vortices, pinned at two -discontinuities situated
at some distance from each other, splitting of the eigenfrequencies occur.
We calculate this splitting numerically as a function of for different
possible ground states. We also discuss the presence of a critical distance
below which two antiferromagnetically ordered vortices form a strongly coupled
``vortex molecule'' that behaves as a single object and has only one eigenmode.Comment: submitted to Phys. Rev. B (
Self-induced magnetic field effects caused by edge currents in parallel array of Josephson junctions
Interaction of hot spots and THz waves in Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks of various geometry
At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson
junctions a hot spot (a region heated to above the superconducting transition
temperature) coexists with regions still in the superconducting state. In the
``cold'' regions cavity resonances can occur, synchronizing the ac Josephson
currents and giving rise to strong coherent THz emission. We investigate the
interplay of hot spots and standing electromagnetic waves by low temperature
scanning laser microscopy and THz emission measurements, using stacks of
various geometries. For a rectangular and a arrow-shaped structure we show that
the standing wave can be turned on and off in various regions of the stack
structure, depending on the hot spot position. We also report on standing wave
and hot spot formation in a disk shaped mesa structure
Magnetic interference patterns in 0-Pi SIFS Josephson junctions: effects of asymmetry between 0 and Pi regions
We present a detailed analysis of the dependence of the critical current I_c
on the magnetic field B of 0, Pi, and 0-Pi
superconductor-insulator-ferromagnet-superconductor Josephson junctions. I_c(B)
of the 0 and Pi junction closely follows a Fraunhofer pattern, indicating a
homogeneous critical current density j_c(x). The maximum of I_c(B) is slightly
shifted along the field axis, pointing to a small remanent in-plane
magnetization of the F-layer along the field axis. I_c(B) of the 0-Pi junction
exhibits the characteristic central minimum. I_c however has a finite value
here, due to an asymmetry of j_c in the 0 and Pi part. In addition, this I_c(B)
exhibits asymmetric maxima and bumped minima. To explain these features in
detail, flux penetration being different in the 0 part and the Pi part needs to
be taken into account. We discuss this asymmetry in relation to the magnetic
properties of the F-layer and the fabrication technique used to produce the
0-Pi junctions
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