| 1. |
- Andersson, Magnus, et al.
(författare)
-
Scaling of the vortex-liquid resistivity in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals
- 2001
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:18, s. 1845111-1845119
-
Tidskriftsartikel (refereegranskat)abstract
- The consequences of a recently proposed model [A. Rydh. O. Rapp. and M. Andersson. Phys. Rev. Lett. 83. 1850 (1999)] for the vortex-liquid resistivity close to a vortex liquid-to-glass transition are anal-zed in detail. We find a detailed quantitative agreement between the model and resistivity measurements on disordered, optimally doped YBa2Cu3O7-delta single crystals. For temperatures below the superconducting transition temperature. a scaling of all measured resistivity curves in magnetic field (0
|
|
| 2. |
- Andersson, Magnus, et al.
(författare)
-
Vortex liquid properties in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 332:1-4, s. 86-92
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical anisotropy, gamma = (m(c)/m(ab))(1/2), can easily be varied by changing the oxygen content in single crystals of YBa2Cu3O7-delta (YBCO); thus making this system useful as a test system For vortex dynamics in high-temperature superconductors (HTSC). Here, some recent results are reviewed. Measurements of the c-axis resistivity with the magnetic field B II ab-plane is shown to be a powerful tool in studying vortex velocity correlations both parallel and perpendicular to the applied field. In optimally doped crystals, we iind evidence that the in-plane vortex lattice melts at T-m into a disentangled vortex liquid, which looses its correlation along the c-axis at a higher temperature T-br > T-m. For weakly disordered crystals and magnetic fields B \\ c-axis, a relation between the vortex glass line and the magnetic field dependence of the characteristic energy, U*, in the pinned vortex liquid is proposed. This approach is shown to give support to our idea of describing the vortex glass resistivity in the liquid regime by a modified glass correlation Length, xi(g) = xi(0)\k(B)T/U-0 - 1\(-nu) which depends on the average pinning energy, Lr,, in the system [A. Rydh, O. Rapp, M. Andersson, Phys. Rev. Lett. 83 (1999) 1850].
|
|
| 3. |
- Andersson, Magnus, et al.
(författare)
-
Vortex liquid resistivity in disordered YBa2Cu3O7-delta single crystals
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1239-1240
-
Tidskriftsartikel (refereegranskat)abstract
- The vortex solid-to-liquid transition line, T-g(B) and the linear resistivity in the vortex liquid of an optimally doped disordered YBa2Cu3O7-delta Single crystal is analyzed in detail. Our previously proposed description [Rydh, Rapp and Andersson, Phys.Rev.Lett. 83 (1999) 1850] is shown to quantitatively describe both T-g(B) and the vortex liquid resistivity above T-g using the same parameters. Furthermore, a comparison with the thermally activated behaviour usually employed to account for the resistivity in the vortex liquid is reported.
|
|
| 4. |
- Andersson, Magnus, et al.
(författare)
-
Vortex liquid-to-solid transition in underdoped YBa2Cu3O7-delta single crystals with B parallel to ab
- 2003
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 388, s. 691-692
-
Tidskriftsartikel (refereegranskat)abstract
- A nearly magnetic field independent vortex liquid-to-solid transition has been observed in both the ab-plane and in the c-axis resistivity of underdoped YBa2Cu3O7-delta single crystals for magnetic fields Bparallel toab-plane. These observations suggest that intrinsic pinning caused by the superconducting layers do neither lead to a system of completely decoupled superconducting layers nor to a smectic vortex phase at high fields. A possible explanation may include a transition driven by changes in elastic properties (e.g., the shear modulus) of the vortex system.
|
|
| 5. |
- Axnas, J., et al.
(författare)
-
Magnetoconductivity of polycrystalline Hg,Tl-1223
- 2000
-
Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1009-1010
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetoconductivity of polycrystalline Hg1-xTlxBa2Ca2Cu3O8+delta With x = 0 and 0.2 has been measured above T-c and analysed in terms of superconducting fluctuations. Such studies are numerous and successful for Y- and Bi-based materials, but still rare for Hg- and Tl-based materials. Results for the coherence lengths and the role of the Maki-Thompson contribution are briefly discussed.
|
|
| 6. |
- Bjornangen, T., et al.
(författare)
-
In-plane anisotropy and chain contribution from the magnetoresistivity of YBa2Cu3O7-delta
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1885-1886
-
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.
|
|
| 7. |
- Bjornangen, T., et al.
(författare)
-
In-plane anisotropy and possible chain contribution to magnetoconductivity in YBa2Cu3O7-delta
- 2001
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 6322:22
-
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.
|
|
| 8. |
- Bjornangen, T., et al.
(författare)
-
Multiterminal transport measurements : In-plane anisotropy and vortex liquid correlation in YBa2Cu3O7-delta
- 2001
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 64:22
-
Tidskriftsartikel (refereegranskat)abstract
- Using a modified pseudoflux transformer geometry, the in-plane anisotropy and vortex-liquid correlation of an untwinned YBa2Cu3O7-delta single crystal have been studied. The square-shaped, multiterminal sample design allows comparative studies of a- and b-axis properties for arbitrarily oriented magnetic fields. We compare the in-plane resistivity in the case of intrinsic pinning with the longitudinal resistivity, i.e., with the resistivity in absence of a macroscopic Lorentz force. The relative ratio between resistivities rho (a) and rho (b) in the vortex state can be made to vary over a wide range by controlling the direction of the applied magnetic field. Evidence is found for almost isotropic fluctuations corresponding to a fluctuation anisotropy gamma (A)(ab)approximate to1.1, noted to be clearly lower than the anisotropy gamma (ab)=1.27 obtained from the vortex phase diagram.
|
|
| 9. |
- Bjornangen, T., et al.
(författare)
-
Vortex liquid and solid correlation in untwinned YBa2Cu3O7-delta
- 2003
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 388, s. 727-728
-
Tidskriftsartikel (refereegranskat)abstract
- Longitudinal- and inter-vortex correlations in an untwinned YBa2Cu3O7-delta single crystal were studied in the liquid and driven solid state, using a modified, symmetric pseudo-flux transformer method. The response of the flowing vortex system below T-m was significantly different along the field (Hparallel toa) and perpendicular to it (Hparallel toc), with both cases probed by an in-plane current mainly parallel to b.
|
|
| 10. |
- Björnängen, Therese, et al.
(författare)
-
Vortex correlation parallel in underdoped and perpendicular to H vertical bar vertical bar ab YBa2Cu3O7-delta
- 2004
-
Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 408-10, s. 564-565
-
Tidskriftsartikel (refereegranskat)abstract
- Vortex correlation in the region of the depinning transition has been studied in twinned YBa2Cu3O7-delta single crystals with T-c approximate to 80 K. Transport properties along the e-axis were performed in magnetic fields parallel to the ab-plane, using the pseudo flux-transformer method. By rotating the sample around the c-axis, both longitudinal and transverse vortex correlation could be studied. Compared to optimally doped samples, transverse vortex velocity correlation was enhanced at high fields, while longitudinal correlation remained qualitatively the same.
|
|
