Flux Flow of Abrikosov-Josephson Vortices along Grain Boundaries in High-Temperature Superconductors (original) (raw)
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Intragranular defects and Abrikosov–Josephson vortices in Bi-2223 bulk superconductors
Journal of Materials Science: Materials in Electronics, 2017
The Abrikosov–Josephson (AJ) vortices that emerge at intragranular defects of Bi-2223 bulk superconductors are detected. The study is based on the combination of magnetic and transport characterizations with a brief theoretical formulation that allow estimating the minimum angle of the intragranular planar defects where the AJ vortices emerges for a given applied magnetic field. Measurements of magnetization versus applied magnetic field, M(H_{a})$$M(Ha), in powder samples reveal that the intrinsic anisotropy effects of the grains in these materials suffer almost a complete attenuation due to their high shape anisotropy. In fact, powder samples behave as composed of isotropic grains with lower critical field ~80 Oe. However, a more detailed analysis of the quasi-linear part of these curves show that the penetration of the magnetic flux into intragranular defects occurs at similar values of applied magnetic fields than those reported in whiskers or well textured ceramics for their ...
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We have directly observed well-separated Josephson vortex splinters with unquantized magnetic flux at asymmetric 45° grain boundaries in YBa2Cu3O7-δ films by imaging magnetic flux with scanning SQUID microscopy. The existence of these splinter vortices has been predicted and is well described by a model based on dx2-y2 pairing symmetry and facetting of the grain boundary on a length scale shorter than the Josephson penetration depth.
Observation of splintered Josephson vortices at grain boundaries in YBa2Cu3O7-d
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We have directly observed well-separated Josephson vortex splinters with unquantized magnetic flux at asymmetric 45 grain boundaries in YBa 2 Cu 3 O 7ÿ films by imaging magnetic flux with scanning SQUID microscopy. The existence of these splinter vortices has been predicted and is well described by a model based on d x 2 ÿy 2 pairing symmetry and facetting of the grain boundary on a length scale shorter than the Josephson penetration depth.
Observation of Splintered Josephson Vortices at Grain Boundaries in YBa2Cu3O7-δ
Physical Review Letters, 2002
We have directly observed well-separated Josephson vortex splinters with unquantized magnetic flux at asymmetric 45 grain boundaries in YBa 2 Cu 3 O 7ÿ films by imaging magnetic flux with scanning SQUID microscopy. The existence of these splinter vortices has been predicted and is well described by a model based on d x 2 ÿy 2 pairing symmetry and facetting of the grain boundary on a length scale shorter than the Josephson penetration depth.
Materials Science, 1970
The 0.3-mm-thick, 50-mm-wide and 100-mm-long YBa2Cu3O7-x superconducting bridges with a laser-written, single, Π-shaped channel have been investigated by means of electronic transport measurements at temperatures below the onset of the bridge's superconducting transition temperature. Our results demonstrate that the coherent vortex motion confined in the P-shaped channel can be used for determination of both the density and velocity of Abrikosov magnetic vortices in the channel. The coherent motion of Abrikosov vortices expresses itself as Josephson-like voltage steps, observed on the current-voltage characteristics of our microbridges, measured at zero external magnetic field, in a limited range of temperatures and bias currents. The steps' amplitude corresponds to the entrance of an additional vortex-antivortex pair into the channel's area and change in the vortex velocity. This amplitude also affects the increase of the Lorentz force for energy dissipative drift of th...
Physical Review B, 1993
The critical fluctuations and pinning effects in the vortex state of twinned superconducting Y-Ba-Cu-O single crystals are investigated. A second-order vortex-solid melting transition is manifested by the uniUersal static and dynamic exponents v= 3 and z =3 and the universal vortex-transport functions, independent of the experimental techniques and the magnitude and orientation of the applied magnetic fields. The vortex-correlation length and the critical-relaxation rate are also determined. The large thermal and disorder fluctuations in the vortex state of high-temperature superconductors (HTS) result in interesting vortex properties which have stimulated intense research effort. ' ' However, it is sti11 controversial whether the "phase boundary" below the meanfield upper critical field in the vortex phase diagram is a vortex-solid "melting transition, "' or an "irreversible line" that defines the onset of vortex "depinning. " Although a first-order vortex-solid melting transition may exist in untwinned, clean-limit single crystals, a secondorder melting transition should be common in most samples with moderate disorder. Such a second-order phase transition, if it exists, should be manifested by universal static and dynamic critical exponents which are indepen; dent of the sample, experimental technique, magnitude, and orientation of the applied magnetic field. However,
Bulletin of Materials Science, 1999
Quantized magnetic flux lines (vortices) in a Nb foil were directly observed in different magnetic fields up to 200 G by a cryo-Lorentz electron microscope. The interaction of vortices with dislocations in the specimen was examined and clarified; edge-on dislocations weakly pin individual vortices at magnetic fields below 100 G. In higher magnetic fields the formation of a regular hexagonal vortex lattice started preferentially at in-plane dislocations. At 200 G the Abrikosov vortex lattice was formed with small domains, whose centre included the dislocations, showing their important role on the formation of the vortex lattice. For a NbTi foil no clear image of vortices could be seen, because the surface was rough due to the formation of fine grains and precipitates.
Interlayer vortices and edge dislocations in high-temperature superconductors
Physical review. B, Condensed matter, 1995
The interaction of an edge dislocation made of half the superconducting plane with a magnetic interlayer vortex is considered within the framework of the Lawrence-Doniach model with negative as well as positive Josephson interlayer coupling. In the first case the binding energy of the vortex and the dislocation has been calculated by employing a variational procedure. The current distribution around the bound vortex turns out to be asymmetric. In the second case the dislocation carries a spontaneous magnetic half-vortex, whose binding energy with the dislocation turns out to be infinite. The halfvortex energy has been calculated by the same variational procedure. Implications of the possible presence of such half-vortices for the properties of high temperature superconductors are discussed.
Journal of Applied Physics, 2007
It has been well established that the critical current density J c across grain boundaries ͑GBs͒ in high-temperature superconductors decreases exponentially with misorientation angle beyond ϳ2°-3°. This rapid decrease is due to a suppression of the superconducting order parameter at the grain boundary, giving rise to weakly pinned Abrikosov-Josephson ͑AJ͒ vortices. Here we show that if the GB plane meanders, this exponential dependence no longer holds, permitting greatly enhanced J c values: up to six times at 0 T and four times at 1 T at ϳ 4°-6°. This enhancement is due to an increase in the current-carrying cross section of the GBs and the appearance of short AJ vortex segments in the GB plane, confined by the interaction with strongly pinned Abrikosov ͑A͒ vortices in the grains.
2008
We present our recent results on the temperature dependence of current-voltage characteristics for polycrystalline Y 1-x Pr x Ba 2 Cu 3 O 7- superconductors with x = 0.0, 0.1 and 0.3. The experimental results are found to be reasonably well fitted for all samples by a power like law of the form ) (T a c I I R V . Here, we assume that a(T)=1+ 0 I C (T)/2k B T and I C (T)=I C (0)(1-T/T C) 3/2 for the temperature dependences of the power exponent and critical current, respectively. According to the theoretical interpretation of the obtained results, nonlinear deviation of our current-voltage characteristics curves from Ohmic behavior (with a(T C)=1) below T C is attributed to the manifestation of dissipation processes. They have a characteristic temperature T p defined via the power exponent as a(T p)=2 and are related to the current induced depinning of Abrikosov vortices. Both T C (x) and T p (x) are found to decrease with an increase of Pr concentration x reflecting deterioration of the superconducting properties of the doped samples.