The analysis of possible phenomena in the superconductor-constriction-superconductor (S-c-S) junctions inserted into microwave circuits is carried out. The results of experiments in which properties of the junctions making them different in comparison with usual nonlinear microwave elements were studied are discussed. The characteristics of receiving devices such as amplifiers, detectors and converters operating on the basis of these phenomena are obtained. The limit characteristics of these devices in different regimes of operation are analysed and compared with experimentally achieved characteristics. It is shown that the noise properties of the receiving devices utilizing the S-c-S junctions close to ideal can be obtained for the frequencies lower than characteristic frequency of the junction. This frequency for known realizations of the S-c-S junctions (point contacts and thin film bridges of small dimensions) can reach of order of 500-1 000 GHz or in other words of the middle of the submillimeter waveband range

A decisive role in electrical transport in high T c superconducting materials with anisotropic pairing, like cuprate superconductors [1,2] and Fe based compounds [3][4][5][6], belongs to grain boundaries (GB). Among a variety of possible crystallographic orienta tions of grains forming a boundary, the [001] tilt GB (see Fig. 1a) had been studied the most intensively with an emphases on the effect of order parameter symmetry and the mechanisms of charge transfer across the GB interface [1,2,[7][8][9][10][11][12][13][14][15].Recently, [100] tilt high T c GB junctions with mutually tilted c axis's (see Fig. 1b) have been fabri cated [16][17][18][19][20][21][22][23][24][25] with an order of magnitude lower GB meandering and up to a threefold increase of the I c R n values [16][17][18][19]. A complete antiphase correlation between low frequency fluctuations of the resistance R n and the critical current I c has been observed in these junctions, thus showing that both quasiparticles and Cooper pairs flow directly through the same regions of the barrier [24]. In spite of intensive efforts, the mech anisms of electrical transport through grain bound aries in high T c superconductors are still far from understanding. This is true not only in respect of phys ics of conductivity of GB itself, but also in respect of influence of normal and supercurrent redistribution in the vicinity of GB on their properties.It is well known that strong anisotropy of resistivity of high T c materials must be taken into account during ¶ The article is published in the original.interpretations of electrical data. A simple assumption that electrical resistivity of the material is proportional to the measured resistance with some coefficient of proportionality given by sample geometry may give an incorrect result [26-36].We developed a self consistent method for the calculation of spatial current distributions in high T c grain boundary junctions. It is found that crystallographic anisotropy of high T c superconducting electrodes results in the effects, which previously were not taken into account for interpretations of experimental data. Among them is a significant redistribution of electrical currents in superconducting electrodes in the vicinity of a grain boundary. In particular in the case of [100] tilt bicrystal junctions, this current redistribution results in a substantial focusing to the top or bottom part of a thickness of the grain boundary, depending on "roof" or "valley" type of the grain boundary. This redistribution is accompanied by generation of vortex currents around the grain boundary, which leads to self biasing of grain boundary junctions by magnetic field nucle ated by these vortex currents. It is shown that twinning or variation of geometrical shape of the high T c elec trode may also result in intensive redistribution of electrical currents and nucleation of local magnetic fields inside a high T c superconducting electrodes. Fig. 1. Schematic diagram showing the crystallography of a [001] tilt boundary (a), a [100] tilt b...

Values for the maximum Josephson critical current ( / : -) and distortion of the dependence of the critical current (I,) on magnetic field applied parallel to the plane of t h e tunnel junction (HI,) are calculated for different configurations of Abrikosov vortices in a wide range of their concentration. An experimental procedure is developed to trap both misaligned dipole vortices and monopole vortices in the NbiAlOJNb Josephson tunnel junction for study of their influence on the/,(Hll) curves and the value of/?. The results of the theoretical calculations agree well with the experimental data.

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We report on experimental results about Josephson junctions for radiation detection with an annular geometry. The observed suppression of the critical Josephson current and the presence of one single resonance step in the current–voltage characteristic, as predicted by the theory, strongly support the idea that this geometry could be very convenient for radiation detection. The results were obtained when one single magnetic fluxon was trapped in the central hole, and they represent the first experimental confirmation of the theoretical predictions in the case of annular junctions with finite ring width.