HTSC group    -    Department of Theoretical Bases of Microelectronics    -    Ioffe Institute

Critical state in HTSC films with B-dependent Jc

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].

Oxygen subsystem in YBaCuO lattice

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