743 research outputs found
Cherenkov radiation from fluxon in a stack of coupled long Josephson junctions
We present a systematic study of the Cherenkov radiation of Josephson plasma
waves by fast moving fluxon in a stack of coupled long Josephson junctions for
different fluxon modes. It is found that at some values of parameters
current-voltage characteristic may exhibit a region of the back-bending on the
fluxon step. In the opposite limit the emission of the Cherenkov radiation
takes place. In the annular junctions of moderate length the interaction of the
emitted waves with fluxon results in the novel resonances which emerge on the
top of the fluxon step. We present more exact formulas which describe the
position of such resonances taking into account difference between junction and
non-linear corrections. The possibility of direct detection of the Cherenkov
radiation in junctions of linear geometry is discussed.Comment: 10 pages, 12 figures, accepted to JLT
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
Geometry-induced phase transition in fluids: capillary prewetting
We report a new first-order phase transition preceding capillary condensation
and corresponding to the discontinuous formation of a curved liquid meniscus.
Using a mean-field microscopic approach based on the density functional theory
we compute the complete phase diagram of a prototypical two-dimensional system
exhibiting capillary condensation, namely that of a fluid with long-ranged
dispersion intermolecular forces which is spatially confined by a substrate
forming a semi-infinite rectangular pore exerting long-ranged dispersion forces
on the fluid. In the T-mu plane the phase line of the new transition is
tangential to the capillary condensation line at the capillary wetting
temperature, Tcw. The surface phase behavior of the system maps to planar
wetting with the phase line of the new transition, termed capillary prewetting,
mapping to the planar prewetting line. If capillary condensation is approached
isothermally with T>Tcw, the meniscus forms at the capping wall and unbinds
continuously, making capillary condensation a second-order phenomenon. We
compute the corresponding critical exponent for the divergence of adsorption.Comment: 5 pages, 4 figures, 5 movie
AC induced damping of a fluxon in long Josephson junction
We present a theoretical and experimental study of Josephson vortex (fluxon)
moving in the presence of spatially homogeneous dc and ac bias currents. By
mapping this problem to the problem of calculating the current-voltage
characteristic of a small Josephson junction, we derive the dependence of the
average fluxon velocity on the dc bias current. In particular we find that the
low frequency ac bias current results in an additional nonlinear damping of
fluxon motion. Such ac induced damping crucially depends on the intrinsic
damping parameter and increases drastically as this parameter is reduced. We
find a good agreement of the analysis with both the direct numerical
simulations and the experimentally measured current-voltage characteristics of
a long annular Josephson junction with one trapped fluxon.Comment: Physical Review B, in pres
Incommensurate dynamics of resonant breathers in Josephson junction ladders
We present theoretical and experimental studies of resonant localized
resistive states in a Josephson junction ladder. These complex breather states
are obtained by tuning the breather frequency into the upper band of linear
electromagnetic oscillations of the ladder. Their prominent feature is the
appearance of resonant steps in the current-voltage (I-V) characteristics. We
have found the resonant breather-like states displaying incommensurate
dynamics. Numerical simulations show that these incommensurate resonant
breathers persist for very low values of damping. Qualitatively similar
incommensurate breather states are observed in experiments performed with
Nb-based Josephson ladders. We explain the appearance of these states with the
help of resonance-induced hysteresis features in the I-V dependence.Comment: 5 pages, 6 figure
Andreev reflection and strongly enhanced magnetoresistance oscillations in GaInAs/InP heterostructures with superconducting contacts
We study the magnetotransport in small hybrid junctions formed by
high-mobility GaInAs/InP heterostructures coupled to superconducting (S) and
normal metal (N) terminals. Highly transmissive superconducting contacts to a
two-dimensional electron gas (2DEG) located in a GaInAs/InP heterostructure are
realized by using a Au/NbN layer system. The magnetoresistance of the S/2DEG/N
structures is studied as a function of dc bias current and temperature. At bias
currents below a critical value, the resistance of the S/2DEG/N structures
develops a strong oscillatory dependence on the magnetic field, with an
amplitude of the oscillations considerably larger than that of the reference
N/2DEG/N structures. The experimental results are qualitatively explained by
taking Andreev reflection in high magnetic fields into account.Comment: 5 pages, 5 figure
Two-tone spectroscopy of a SQUID metamaterial in the nonlinear regime
Compact microwave resonantors made of superconducting rings containing
Josephson junctions (SQUIDs) are attractive candidates for building frequency
tunable metamaterials with low losses and pronounced nonlinear properties. We
explore the nonlinearity of a SQUID metamaterial by performing a two-tone
resonant spectroscopy. The small-amplitude response of the metamaterial under
strong driving by a microwave pump tone is investigated experimentally and
theoretically. The transmission coefficient of a weak probe signal is
measured in the presence of the pump tone. Increasing the power of the pump, we
observe pronounced oscillations of the SQUID's resonance frequency
. The shape of these oscillations varies significantly with
the frequency of the pump tone . The response to the probe
signal displays instabilities and sidebands. A state with strong second
harmonic generation is observed. We provide a theoretical analysis of these
observations, which is in good agreement with the experimental results
Fluxon-semifluxon interaction in an annular long Josephson 0-pi-junction
We investigate theoretically the interaction between integer and half-integer
Josephson vortices (fluxons and semifluxons) in an annular Josephson junction.
Semifluxons usually appear at the 0--boundary where there is a
-discontinuity of the Josephson phase. We study the simplest, but the most
interesting case of one -discontinuity in a loop, which can be created
only artificially. We show that measuring the current-voltage characteristic
after injection of an integer fluxon, one can determine the polarity of a
semifluxon. Depending on the relative polarity of fluxon and semifluxon the
static configuration may be stable or unstable, but in the dynamic state both
configurations are stable. We also calculate the depinning current of
fluxons pinned by an arbitrary fractional vortex.Comment: 8pages, 6 figures, submitted to PR
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