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| Author |
López, D.; Decca, R.; de la Cruz, F. |
| Title |
Topological pinning and flux flow in ceramic superconductors |
Type |
Journal Article |
Year  |
1991 |
Publication |
Solid State Communications |
Abbreviated Journal |
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| Volume |
79 |
Issue |
11 |
Pages |
959-962 |
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| Abstract |
The transport current dissipation in the high Tc superconducting ceramic La1.85Sr0.15CuO4−δ shows a sin2 Θ voltage dependence where Θ is the angle between the transport current and the magnetic field. This result and the experimental evidence of an angle independent critical current cannot be explained by the conventional description of flux motion in homogeneous type II superconductors. The results are analyzed in the framework of a granular system where pinning is induced by the topological distribution of current flowing through a multiply connected medium. The dissipation in the superconducting state is found to be due to two additive contributions, one induced by the movement of magnetic flux and the other associated to dissipation in the Josephson junction. |
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0038-1098 |
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BT @ pedrazp @ |
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808 |
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| Author |
Safar, H.; Rodriguez, E.; de la Cruz, F.; Gammel, P.L.; Schneemeyer, L.F.; Bishop, D.J. |
| Title |
Observation of two-dimensional vortices in Bi2Sr2CaCu2Ox |
Type |
Journal Article |
| Year |
1992 |
Publication |
Physical Review B |
Abbreviated Journal |
Phys. Rev. B |
| Volume |
46 |
Issue |
21 |
Pages |
14238-14241 |
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| Abstract |
We report transport measurements in the mixed state of single crystals of Bi2Sr2CaCu2Ox using a modified version of the dc flux transformer geometry pioneered by Giaever in low-Tc materials. We find that over a wide range of the phase diagram the vortices are effectively two dimensional in character. Our results suggest that vortex cutting is an efficient process and that it is unlikely that the vortices are strongly entangled in this region of the phase diagram. |
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American Physical Society |
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BT @ pedrazp @ 10.1103/PhysRevB.46.14238 |
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801 |
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| Author |
López, D.; Rodríguez, E.; Nieva, G.; de la Cruz, F.; Cheong, S. W. |
| Title |
Three-dimensional vortex flux flow in LSCO and YBCO through pseudo dc flux transformer measurements |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physica B: Condensed Matter |
Abbreviated Journal |
Physica B |
| Volume |
194-196 |
Issue |
2 |
Pages |
1977-1978 |
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| Abstract |
A pseudo dc flux transformer configuration shows that the flux flow in La2−xSrxCuO4 (x=0.075) and YBa2Cu3O7 single crystals is due to the movement of 3-D vortices across the sample. We show that the loss of c-axis long range vortex correlation is achieved either by thermal fluctuations or by an inhomogeneus Lorentz force acting on the vortices. |
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BT @ gnieva @ |
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442 |
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Safar, H.; Gammel, P.L.; Huse, D.A.; Majumdar, S.N.; Schneemeyer, L.F.; Bishop, D.J.; Lopez, D.; Nieva, G.L.; de la Cruz, F. |
| Title |
Observation of a nonlocal conductivity in the mixed state of YBa2Cu3O7-d: Experimental evidence for a vortex line liquid |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physical Review Letters |
Abbreviated Journal |
Phys. Rev. Lett. |
| Volume |
72 |
Issue |
8 |
Pages |
1272 |
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| Abstract |
We report on transport measurements in the mixed state of YBa2Cu3O7 single crystals using the dc flux transformer geometry. In the vortex fluid regime we have observed the onset of a nonlocal conductivity. At lower temperatures, close to but above the phase transition temperature the vortices become effectively three dimensional in character. This is in sharp contrast to recent flux transformer experiments on Bi2Sr2CaCu2O which have failed to see a nonlocal conductivity, confirming the two-dimensional character at high temperatures of the vortices in that system. These observations suggest that in a finite temperature interval, the vortex state in YBa2Cu3O7 is a line liquid. |
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BT @ gnieva @ |
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443 |
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| Author |
López, D.; Nieva, G.; de la Cruz, F. |
| Title |
In- and out-of-plane vortex correlations in YBa2Cu3O7 |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physical Review B |
Abbreviated Journal |
Phys. Rev. B |
| Volume |
50 |
Issue |
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Pages |
7219 |
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BT @ gnieva @ |
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444 |
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| Author |
López, D.; Nieva, G.; de la Cruz, F.; Jensen, Henrik Jeldtoft; O’Kane, Dominic |
| Title |
Flux cutting in YBa2Cu3O7-δ single crystals: Experiment and phenomenological model |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physical Review B |
Abbreviated Journal |
Phys. Rev. B |
| Volume |
50 |
Issue |
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Pages |
9684 |
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| Abstract |
We measured the current-induced loss of vortex correlation in YBa2Cu3O7-δ crystals using the pseudo-dc-flux-transformer geometry. We find that the current density Jcut at which the top and bottom voltage drops differ is a linear function of temperature, is independent of pinning, and depends on the thickness of the sample. This thickness dependence strongly suggests that the electrical current flows at the surface of the sample. The observed behavior with temperature, magnetic field, and thickness is described by a phenomenological model. |
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BT @ gnieva @ |
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445 |
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Safar, H.; Lopez, D.; Gammel, P.L.; Huse, D.A.; Majumdar, S.N.; Schneemeyer, L.F.; Bishop, D.J.; Nieva, G.; de la Cruz, F. |
| Title |
Experimental evidence of a non-local resistivity in a vortex line liquid |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physica C: Superconductivity |
Abbreviated Journal |
Physica C |
| Volume |
235-240 |
Issue |
4 |
Pages |
2581-2582 |
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| Abstract |
We present transport measurements on YBCO single crystals in the vortex liquid regime using the DC flux transformer geometry. We show that the data are inconsistent with the material being an anisotropic, local conductor. The results provided evidence for non-local transport which indicate that there can be correlated vortex motion over macroscopic distances in this system. We have shown that this correlated vortex motion can be destroyed by either thermal fluctuations or the applications of large driving forces. |
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BT @ gnieva @ |
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450 |
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López, D.; Nieva, G.; de la Cruz, F. |
| Title |
Long range correlations of the vortex structure in YBCO single crystals |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physica C: Superconductivity |
Abbreviated Journal |
Physica C |
| Volume |
235-240 |
Issue |
4 |
Pages |
2575-2576 |
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Transport measurements in the mixed state of YBa2Cu3O7 single crystals using the “DC flux transformer” configuration show that the glass-liquid phase transition at the irreversibility line, TI(H), behaves as a three dimensional vortex phase transition. These results together with resistance measurements in the c direction show that the vortex correlation across the sample is destroyed at a temperature Tth(H), higher than TI(H). The sample thickness dependence of Tth(H) suggest that in the real thermodynamic phase transition (infinite sample), the long range correlation in the ab plane as well in the c direction is lost at the single temperature TI(H). |
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BT @ gnieva @ |
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451 |
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de la Cruz, F.; Pastoriza, H.; López, D.; Goffman, M. F.; Arribére, A.; Nieva, G. |
| Title |
Consequences of 3D-2D vortex decoupling on the phase diagram of HTS |
Type |
Journal Article |
| Year |
1994 |
Publication |
Physica C: Superconductivity |
Abbreviated Journal |
Physica C |
| Volume |
235-240 |
Issue |
1 |
Pages |
83-86 |
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We discuss the quench of the long range order in the direction parallel and perpendicular to the field, in the mixed state of BSCCO(2212) and YBCO(123) single crystals. The experimental data show that the high temperature vortex phase in both systems is an uncorrelated liquid phase in all directions. |
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no |
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BT @ gnieva @ |
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453 |
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| Author |
de la Cruz, F.; López, D.; Nieva, G. |
| Title |
Thermally induced change in the vortex dimensionality of YBa2Cu3O7 single crystals |
Type |
Journal Article |
| Year |
1994 |
Publication |
Philosophical Magazine Part B |
Abbreviated Journal |
Philos. Mag. B |
| Volume |
70 |
Issue |
3 |
Pages |
773 - 786 |
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Transport measurements in YBa2Cu3O7 single crystals using a modification of the d.c. flux transformer configuration are reported. We show that, for applied magnetic fields in the crystallographic c direction, the vortex correlation length in this direction is reduced to values smaller than the thickness of the sample. The reduction can be induced either by thermal disorder (linear response) or by flux cutting after the vortices reach a critical velocity (nonlinear response). The results show that, in the transition from a vortex-glass state to a vortex-liquid state, the vortices are effectively three dimensional in character. A two-dimensional regime is induced at higher temperatures well inside the reversibility region. |
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BT @ gnieva @ |
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456 |
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