Exact theoretical results are
obtained for critical state of thin superconductors with field-dependent
critical current, Jc.
We have determined that the low-field peak in major magnetization
loops of thin strips [1]
is found at zero applied field for any Jc(B)-dependence.
We calculated flux and
current distributions as well as magnetization and ac susceptibility for a thin disk
[2]
with a general Jc(B)-dependence.
Spatial inhomogeneity of HTSC films
Due to anomalously small coherence length and a very complicated crystal
structure properties of HTSC are strongly affected by various spatial inhomogeneities.
We have studied effect of Tc-inhomogeneity on resistance
[1,2] and its noise
[2,3,7]
in the vicinity of superconducting transition; methods to measure Tc-inhomogeneity
by low-temperature SEM [1,4];
correlation between Tc- and jc-inhomogeneity
[5,6] observed by magneto-optical
imaging and relation of spatial inhomogeneities to cation defect formation
[8].
Magnetic flux penetration
into HTSC films
Penetration of magnetic flux
into HTSC samples of various shapes can now be easily visualized by magneto-optical
and other spatially-resolved techniques. We studied flux penetration into
a thin current-carrying strip and compared experimental results with the
Bean model predictions and our flux creep simulations [1].
Besides, we observed an evolution of flux distribution after switching
on transport current [2].
Using magneto-optical imaging
a temperature dependence of filament coupling in Bi-2223 tapes have been
studied [3].
We also studied a large- and small-scale structure of flux distrbution in various
current-carrying states of Bi-2223 tapes
[4].
Resistance flicker noise
Studies of flicker noise are of great interest because, first, this noise
limits sensitivity of HTSC devices, and, second, such studies present a
powerful tool to characterize a degree of structural disorder. We have
studied resistance flicker noise in the normal phase [1]
and in the vicinity of Tc [2]
as well as noise of a single latent weak link below the transition [3].
Theoretical models for noise associated with local fluctuations of Tc
[4] as well as with temperature fluctuations [5]
have been considered.
Novel HF devices
Some ideas are suggested for fabrication of new and advancement of existing
HF devices based on HTSC. A parametric resonance due to temperature oscillations
in superconducting micron-scale waveguides under laser beam irradiation
is suggested for the creation of high-sensitivity tuneable filters [1].
Use of the resonance effect in bolometers based on superconductors in the
zero-resistance state is suggested to reach the signal/noise ratio above
that of conventional bolometers [2].