| 1. |
- Bjornangen, T., et al.
(författare)
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In-plane anisotropy and chain contribution from the magnetoresistivity of YBa2Cu3O7-delta
- 2000
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1885-1886
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Tidskriftsartikel (refereegranskat)abstract
- Magnetoresistivity measurements were made in untwinned YBa2Cu3O7-delta above T-c for B\\c and B\\ab, with I\\a or b. A fluctuation theory that allows for an in-plane coherence length anisotropy (gamma = xi (b)/xi (a)) was used to determine gamma. The contribution to the magnetoconductivity from the CuO-chains was also analyzed.
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| 2. |
- Bjornangen, T., et al.
(författare)
-
In-plane anisotropy and possible chain contribution to magnetoconductivity in YBa2Cu3O7-delta
- 2001
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 6322:22
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Tidskriftsartikel (refereegranskat)abstract
- The magnetoresistivity of untwinned YBa2Cu3O7-delta Single crystals was measured in magnetic fields up to 12 T-c for B parallel toc and B parallel to ab. at temperatures up to T-c + 84 K and T-c + 50 K, respectively. Two issues were addressed; determination of the in-plane coherence length anisotropy gamma=xi (b)/xi (a) and discussion of the role of the CuO chains in the magnetoconductivity Delta sigma. A fluctuation conductivity theory that allows for an in-plane coherence length anisotropy (xi (a)not equal xi (b)) as well as an extension of the usual Aronov-Hikami-Larkin theory that does not, were used in analyses. The results suggest that the anisotropy gamma is close to 1. The analyses also suggest a contribution to the magnetoconductivity from the CuO chains of a sign which depends on the direction between held and current.
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| 3. |
- Han, S. H., et al.
(författare)
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Studies of dynamic critical behaviour in YBa2Cu3O7-delta single crystals
- 2000
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1855-1856
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Tidskriftsartikel (refereegranskat)abstract
- Up to now, the value of the dynamic critical exponent z is still an open question. We have studied this exponent in the intermediate (XY) critical regime in zero field for a set of high quality YBa2Cu3O7-delta Single crystals in terms of Fisher-Fisher-Huse (FFH) dynamic scaling, and using previously obtained values for the critical exponents cu of the de critical conductivity fluctuations. In this regime (i.e. the absence of Coulomb interactions), one would expect model-E dynamics (z = 1.5) to apply with the conserved charge-density conjugate to the phase fluctuations. However, we find the dynamic critical exponent to be z = 2, which is in agreement with the suggestion of FFH that due to plasma fluctuations, fully relaxational dynamics, model A (z = 2), should be appropriate.
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| 4. |
- Han, S. H., et al.
(författare)
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Three-dimensional XY critical fluctuations of the dc electrical conductivity in Bi2Sr2CaCu2O8+delta single crystals
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:17, s. 11776-11779
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented to analyze the dc critical fluctuation conductivity Delta sigma of Bi2Sr2CaCu2O8+delta single crystals in zero magnetic field. Two crossovers are obtained upon approaching T-c; first the Ginzburg crossover from the mean-held region to the initial critical regime, where the critical exponent a of Delta sigma changes from -1/2 to -2/3, and then, closer to T-c, a crossover of alpha form -2/3 to 1/3 in the critical region. Good agreement is found with the expectations from the three-dimensional XY model.
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| 5. |
- Lundqvist, Björn, et al.
(författare)
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Nearly field-independent in-plane vortex solid-to-liquid transition in the c-axis resistivity of oxygen deficient single crystals of YBa2Cu3O7-delta
- 2001
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 64:6, s. 060503-
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Tidskriftsartikel (refereegranskat)abstract
- The c-axis resistivity has been measured in oxygen deficient single crystals of YBa2Cu3O7-delta (anisotropy gamma approximate to 24-29) with the magnetic field B accurately aligned parallel to the ab plane. An almost field-independent vortex solid-to-liquid transition is observed at high fields in contrast to the usual field-dependent one, which is recovered for a small misalignment between B and ab. This observation challenges previous interpretations of the same effect in the ab resistivity as coming from a smectic vortex state or a decoupling of the superconducting planes.
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| 6. |
- Rapp, Östen., et al.
(författare)
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Resistivity studies by multiterminal transport measurements on single crystal YBa2Cu3O7-delta
- 2003
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Ingår i: Journal of Low Temperature Physics. - 0022-2291 .- 1573-7357. ; 131:06-maj, s. 1009-1018
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Tidskriftsartikel (refereegranskat)abstract
- Multiterminal transport studies provide a powerful technique to investigate vortex structure and correlations in the vicinity of the vortex solid-to-liquid transition in single crystals of high temperature superconductors. Recent results are described, including new contact configurations, allowing both longitudinal and transverse vortex correlations to be studied in one crystal during a single temperature sweep at constant field.
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