The current–voltage (I–V) characteristics of break junctions of polycrystalline La1.85Sr0.15CuO4, Y0.75Lu0.25Ba2Cu3O7−δ, Bi1.8Pb0.3Sr1.9Ca2Cu3Ox and composite YBa2Cu3O7−δ+Ag are investigated. The ...experimental I–V curves exhibit the specific peculiarities of superconductor/normal-metal/superconductor junctions. The relation between an I–V characteristic of network of weak links and I–V dependencies of typical weak links is suggested to describe the experimental data. The I–V curves of typical weak links are calculated by the Kümmel–Gunsenheimer–Nicolsky model considering the multiple Andreev reflections.
The current-voltage characteristics of a porous superconductor Bi
2
Sr
2
Ca
2
Cu
3
O
x
(Bi2223) have been measured at temperatures in the range from 10 to 90 K in magnetic fields of 0–80 kOe. The ...experimental dependences have been analyzed within the model allowing for pinning by clusters of a normal phase with fractal boundaries, as well as the model taking into account phase transformations of vortex matter. It has been found that the electrical resistance of the superconductor material significantly increases at temperatures of 60–70 K over the entire range of magnetic fields under consideration without changing in the sign of the curvature of the dependence
R
(
I
). It has been assumed that this behavior is associated with the specific feature of the pinning in a highly porous high-temperature superconductor, which lies in the fractality of the distribution of pinning centers in a wide range of self-similarity scales. The studied material at the aforementioned temperatures is characterized by the melting of the vortex structure.
Magnetoresistance curves
R(
H) and time relaxation of the residual resistance of bulk YBCO
+
CuO composites have been studied. These composites represent the network of Josephson junctions, where CuO ...acts as a barrier between YBCO grains. It has been shown that hysteresis of the
R(
H) dependences is related to the flux trapping within the YBCO crystallites. This flux induces magnetic field in the intergrain media. Time relaxation of the residual resistance is caused by relaxation of the magnetization of YBCO grains. The time dependence of the residual resistance obeys a logarithmic law, which describes the Anderson-like relaxation processes in the YBCO grains.
The transport properties of a novel foamed superconductor Bi1.8Pb0.3Sr1.9Ca2Cu3Ox have been studied. As the analysis of resistive transitions in a magnetic field shows, the dissipation follows a ...thermally activated flux creep model with the temperature-independent pinning potential in S-N-S-type Josephson junctions.
The construction of a solenoid with nanostructured Cu-Nb wire winding is studied and its electromagnetic, mechanical, and thermal parameters are analytically and numerically calculated. Comparing the ...results of the calculation and testing, the solenoid operability at an amplitude strength of the generated magnetic field of 40 T and a pulse length of 20 ms is established. The obtained parameters make the solenoid applicable in experimental research aimed at solving topical fundamental problems.
The hysteretic behavior of critical current jC(H) and magneto-resistance R(H) of composites Y-Ba-Cu-O+CuO have been studied and presented. The composites represent the network of tunnel-type ...Josephson junctions where copper oxide acts as a material forming barriers between superconducting (YBCO) crystallites. The characteristic features of R(H) and jC(H) dependences are discussed in the frames of the conception of 'two level superconducting system' (the Josephson media and HTSC crystallites) which is realized in the composites under study.
HTSC Bi
1.8Pb
0.3Sr
2Ca
2Cu
3O
x
of low density has been synthesized and its structural and physical properties have been studied. Scanning electron microscopy (SEM) image shows that the material ...obtained has porous “foam” structure. The levitation force measured for the porous Bi
1.8Pb
0.3Sr
2Ca
2Cu
3O
x
is appeared to be approximately the same as for polycrystalline YBCO of high density. These “foam” structures may be an ideal material for some practical applications of HTSCs in bulk form.
The dependence of magnetization on magnetic field M(H) was measured for textured BSCCO samples in directions H‖c,H‖ab at different temperatures. Inclusion of the pinning parameter in the ...Valkov–Khrustalev model V.V. Valkov, B.P. Khrustalev, JETP 80 (1995) 680 allowed to describe successfully the asymmetric M(H) dependencies. The temperature and magnetic field dependencies of critical current and pinning parameter for H‖c and H‖ab were estimated.
The transport properties of the two phases composites based on Y3/4Lu1/4Ba2Cu3O7 (YBCO) and Y3(Al1-xFex)5O12 (x=0.0...1.0) have been studied to investigate the effect of magnetic ordering in garnet ...on superconducting properties of the composites. The composites represent network of Josephson junctions where the non-superconducting ingredient (garnet) acts as barriers separating YBCO grains. It is found that magneto-active ions (Fe) in garnet are responsible for an additional suppression of Josephson coupling in the composites. At some critical concentration of Fe atoms full suppression of super current is observed in a temperature range from TC of YBCO grains down to the characteristic temperature Tm. This behavior is attributed to the interaction of super current carriers with spins of Fe atoms located in the barriers. The crossover from S-I-S (S - superconductor, I - insulator) to S-F-S (F - ferrimagnet) junctions is observed in the composites Y3/4Lu1/4Ba2Cu3O7+Y3(Al1-xFex)5O12 with x increase.
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