927 research outputs found
Strength diagrams of fibrous composites with unidirectional structure
The dependence of the composite strength on the volume proportion of fiber and the transfer factor is analyzed. Four types of diagrams are constructed for the strength of composites as a function of the volume proportion of fibers and the transfer factor
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
Microwave-induced flow of vortices in long Josephson junctions
We report experimental and numerical study of microwave-induced flow of
vortices in long Josephson junctions at zero dc magnetic field. Our intriguing
observation is that applying an ac-bias of a small frequency and
sufficiently large amplitude changes the current-voltage characteristics
(- curve) of the junction in a way similar to the effect of dc magnetic
field, well known as the flux-flow behavior. The characteristic voltage of
this low voltage branch increases with the power of microwave radiation as
with the index . Experiments
using a low-temperature laser scanning microscope unambiguously indicate the
motion of Josephson vortices driven by microwaves. Numerical simulations agree
with the experimental data and show strongly {\it irregular} vortex motion. We
explain our results by exploiting an analogy between the microwave-induced
vortex flow in long Josephson junctions and incoherent multi-photon absorption
in small Josephson junctions in the presence of large thermal fluctuations. In
the case of long Josephson junctions the spatially-temporal chaos in the vortex
motion mimics the thermal fluctuations. In accordance with this analogy, a
control of the intensity of chaos in a long junction by changing its damping
constant leads to a pronounced change in the shape of the - curve. Our
results provide a possible explanation to previously measured but not yet
understood microwave-driven properties of intrinsic Josephson junctions in
high-temperature superconductors.Comment: 8 pages, 13 figure
Spatial and frequency dependencies of local photoresponse of HTS strip-line resonator in regime of two-tone microwave intermodulation excitation
A new phenomenological approach to spatially-resolved research of nonlinear
(NL) microwave properties of operating thin-film superconducting resonators is
proposed. The approach is based on frequency and spatial singularity of Laser
Scanning Microscopy (LSM) images that can be extracted from a set of 2-D
patterns representing x-y distribution of the LSM photoresponse, PR(x, y), at
fixed third-order intermodulation (IMD) frequencies 2f1-f2 and 2f2-f1 as a
result of two-tone resonator microwave excitation at equidistant frequencies f1
and f2 relative to the fundamental resonance, f0. It was shown by us earlier
that the total LSM PR(x, y) originates from two independent (resistive, PRR(x,
y), and inductive, PRX(x, y)) contributions which can be extracted directly
from the LSM images acquired at f1 and f2 by using a method of
spatially-resolved complex impedance partition [1]. Here, we show that
practically the same manipulation of LSM images at 2f1-f2 and 2f2-f1 can be
used to present NL components of IMD LSM PR(x, y) in terms of its independent
spatial variations of (i) inductive IMD_IND(x, y) and (ii) resistive IMD_RES(x,
y) contributions reflecting the origin of the local sources of microwave NL.
[1] A.P. Zhuravel, S.M. Anlage, and A.V. Ustinov, Appl. Phys. Lett., vol. 88,
p. 212503, 2006.Comment: 3 pages, 4 figures, submitted to the Seventh International Kharkov
Symposium (MSMW'10) Proceeding
Imaging of Microscopic Sources of Resistive and Reactive Nonlinearities in Superconducting Microwave Devices
The technique of low-temperature Laser Scanning Microscopy (LSM) has been
applied to the investigation of local microwave properties in operating
YBa2Cu3O7/LaAlO3 thin-film resonators patterned into a meandering strip
transmission line. By using a modified newly developed procedure of
spatially-resolved complex impedance partition, the influence of inhomogeneous
current flow on the formation of nonlinear (NL) microwave response in such
planar devices is analyzed in terms of the independent impact from resistive
and inductive components. The modified procedure developed here is dramatically
faster than our previous method. The LSM capability to probe the spatial
variations of two-tone, third-order intermodulation currents on micron length
scales is used to find the 2D distribution of the local sources of microwave
NL. The results show that the dominant sources of microwave NL are strongly
localized in the resistive domains.Comment: 4 pages, 6 figures, 2-column format,submitted for the 2006 Applied
Superconductivity Conferenc
Quantum dissociation of a vortex-antivortex pair in a long Josephson junction
We report a theoretical analysis and experimental observation of the quantum
dynamics of a single vortex-antivortex (VAV) pair confined in a long narrow
annular Josephson junction. The switching of the junction from the
superconducting state to the resistive state occurs via the dissociation of a
pinned VAV pair. The pinning potential is controlled by external magnetic field
and dc bias current . We predict a specific magnetic field dependence of
the oscillatory energy levels of the pinned VAV state and the crossover to a
{\it macroscopic quantum tunneling} mechanism of VAV dissociation at low
temperatures. Our analysis explains the experimentally observed {\it increase}
of the width of the switching current distribution with and the
crossover to the quantum regime at the temperature of about 100 mK.Comment: 4 pages, 3 figure
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