12,108 research outputs found
Synchronization of One Dimensional Array of Point Josephson Junctions Coupled to a Common Load
We study the synchronization in a one dimensional array of point Josephson
junctions coupled to a common capacitor, which establishes a long-range
interaction between junctions and synchronizes them. The stability diagram of
synchronization in a noise-free system is obtained. The current when junctions
transform from resistive state into superconducting state, is then calculated
and its dependence on the shunt parameters and the dissipation of junctions is
revealed. In the presence of thermal noise, the synchronized oscillations are
destroyed at a critical temperature and the system undergoes a continuous phase
transition of desynchronization. A possible stability diagram of the
synchronized oscillations with respect to thermal noise, current, dissipations
and shunt capacitance is then constructed. Finally we investigate the dynamic
relaxation from random oscillations into synchronized state. The relaxation
time increases with the system size and temperature, but is reduced by the
shunt capacitor.Comment: 11.2 pages, 14 figure
Dispersionless motion in a driven periodic potential
Recently, dispersionless (coherent) motion of (noninteracting) massive
Brownian particles, at intermediate time scales, was reported in a sinusoidal
potential with a constant tilt. The coherent motion persists for a finite
length of time before the motion becomes diffusive. We show that such coherent
motion can be obtained repeatedly by applying an external zero-mean square-wave
drive of appropriate period and amplitude, instead of a constant tilt. Thus,
the cumulative duration of coherent motion of particles is prolonged. Moreover,
by taking an appropriate combination of periods of the external field, one can
postpone the beginning of the coherent motion and can even have coherent motion
at a lower value of position dispersion than in the constant tilt case.Comment: 4 pages, 4 figure
Charged currents, color dipoles and xF_3 at small x
We develop the light-cone color dipole description of highly asymmetric
diffractive interactions of left-handed and right-handed electroweak bosons. We
identify the origin and estimate the strength of the left-right asymmetry
effect in terms of the light-cone wave functions. We report an evaluation of
the small-x neutrino-nucleon DIS structure functions xF_3 and 2xF_1 and present
comparison with experimental data.Comment: 11 pages, 3 figures, misprints correcte
Zurek-Kibble Mechanism for the Spontaneous Vortex Formation in Josephson Tunnel Junctions: New Theory and Experiment
New scaling behavior has been both predicted and observed in the spontaneous
production of fluxons in quenched annular Josephson tunnel
junctions as a function of the quench time, . The probability
to trap a single defect during the N-S phase transition clearly follows an
allometric dependence on with a scaling exponent , as
predicted from the Zurek-Kibble mechanism for {\it realistic} JTJs formed by
strongly coupled superconductors. This definitive experiment replaces one
reported by us earlier, in which an idealised model was used that predicted
, commensurate with the then much poorer data. Our experiment
remains the only condensed matter experiment to date to have measured a scaling
exponent with any reliability.Comment: Four pages, one figur
Investigation of resonant and transient phenomena in Josephson junction flux qubits
We present an analytical and computational study of resonances and transient
responses in a classical Josephson junction system. A theoretical basis for
resonances in a superconducting loop with three junctions is presented,
outlining both the direct relationship between the dynamics of single- and
multi-junction systems, and the direct relationships between observations of
the classical counterparts to Rabi oscillations, Ramsey fringes, and spin echo
oscillations in this class of systems. We show simulations data along with
analytical analyses of the classical model, and the results are related to
previously reported experiments conducted on three junction loops. We further
investigate the effect of off-resonant microwave perturbations to, e.g., the
Rabi-type response of the Josephson system, and we relate this response back to
the nonlinear and multi-valued resonance behavior previously reported for a
single Josephson junction. The close relationships between single and
multi-junction behavior demonstrates the underlying dynamical mechanism for a
whole class of classical counterparts to expected quantum mechanical
observations in a variety of systems; namely the resonant and transient
behavior of a particle in an anharmonic potential well with subsequent escape.Comment: 11 pages, seven figure
Anomalous transport in biased ac-driven Josephson junctions: Negative conductances
We investigate classical anomalous electrical transport in a driven,
resistively and capacitively shunted Josephson junction device. Novel transport
phenomena are identified in chaotic regimes when the junction is subjected to
both, a time periodic (ac) and a constant, biasing (dc) current. The dependence
of the voltage across the junction on the dc-current exhibits a rich diversity
of anomalous transport characteristics: In particular, depending on the chosen
parameter regime we can identify so termed absolute negative conductance around
zero dc-bias, the occurrence of negative differential conductance and, after
crossing a zero conductance, the emergence of a negative nonlinear conductance
in the non-equilibrium response regime remote from zero dc-bias.Comment: 7 pages, 5 figure
Diffusion Enhancement in a Periodic Potential under High-Frequency Space-Dependent Forcing
We study the long-time behavior of underdamped Brownian particle moving
through a viscous medium and in a systematic potential, when it is subjected to
a space-dependent high-frequency periodic force. When the frequency is very
large, much larger than all other relevant system-frequencies, there is a
Kapitsa time-window wherein the effect of frequency dependent forcing can be
replaced by a static effective potential. Our new analysis includes the case
when the forcing, in addition to being frequency-dependent, is space-dependent
as well. The results of the Kapitsa analysis then lead to additional
contributions to the effective potential. These are applied to the numerical
calculation of the diffusion coefficient (D) for a Brownian particle moving in
a periodic potential. Presented are numerical results, which are in excellent
agreement with theoretical predictions and which indicate a significant
enhancement of D due to the space-dependent forcing terms. In addition we study
the transport property (current) of underdamped Brownian particles in a ratchet
potential.Comment: RevTex 6 pages, 5 figure
Spontaneous Fluxon Production in Annular Josephson Tunnel Junctions in the Presence of a Magnetic Field
We report on the spontaneous production of fluxons in the presence of a
symmetry-breaking magnetic field for annular Josephson tunnel junctions during
a thermal quench. The dependence on field intensity of the probability
to trap a single defect during the N-S phase transition drastically
depends on the sample circumferences. We show that the data can be understood
in the framework of the Kibble-Zurek picture of spontaneous defect formation
controlled by causal bounds.Comment: Submitted to Phys. Rev. B with 5 figures on Nov. 15, 200
New Experiments for Spontaneous Vortex Formation in Josephson Tunnel Junctions
It has been argued by Zurek and Kibble that the likelihood of producing
defects in a continuous phase transition depends in a characteristic way on the
quench rate. In this paper we discuss an improved experiment for measuring the
Zurek-Kibble scaling exponent for the production of fluxons in
annular symmetric Josephson Tunnel Junctions. We find .
Further, we report accurate measurements of the junction gap voltage
temperature dependence which allow for precise monitoring of the fast
temperature variations during the quench.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
DMRG analysis of the SDW-CDW crossover region in the 1D half-filled Hubbard-Holstein model
In order to clarify the physics of the crossover from a spin-density-wave
(SDW) Mott insulator to a charge-density-wave (CDW) Peierls insulator in
one-dimensional (1D) systems, we investigate the Hubbard-Holstein Hamiltonian
at half filling within a density matrix renormalisation group (DMRG) approach.
Determining the spin and charge correlation exponents, the momentum
distribution function, and various excitation gaps, we confirm that an
intervening metallic phase expands the SDW-CDW transition in the weak-coupling
regime.Comment: revised versio
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