| 1. |
- Andersson, Magnus, et al.
(författare)
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Vortex liquid properties in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals
- 2000
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 332:1-4, s. 86-92
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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].
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| 2. |
- Andersson, Magnus, et al.
(författare)
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Vortex liquid-to-solid transition in underdoped YBa2Cu3O7-delta single crystals with B parallel to ab
- 2003
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 388, s. 691-692
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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.
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| 3. |
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| 4. |
- Lundqvist, Björn, et al.
(författare)
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Cutoff of the vortex-glass behavior in Tl(2)Ba(2)CaCu(2)O(8+delta) superconducting thin films
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:10, s. 6580-6584
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Tidskriftsartikel (refereegranskat)abstract
- The vortex dynamics of a Tl(2)Ba(2)CaCu(2)O(8+delta) thin film has been measured by electrical resistivity and I-V characteristics. The temperature T*(B) defined from a vortex-glass analysis of the resistivity in the vortex liquid state using the Vogel-Fulcher relation is shown to be consistent with a vortex-glass-like scaling of the I-V characteristics in the high dissipation regime. Below T*, there is however a significant temperature range in which the flux creep does not vanish at low currents. This suggests that the transition into a glassy vortex state is cut off at some length scale.
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| 5. |
- Lundqvist, Björn, et al.
(författare)
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Empirical scaling of the vortex glass line above 1T for high-T(c) superconductors of varying anisotropy
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:22, s. 14064-14067
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Tidskriftsartikel (refereegranskat)abstract
- The resistive transition into a glassy vortex state in oxygen-deficient YBa(2)CU(3)O(7-delta) twinned single crystals of varying anisotropy gamma (8.7 less than or equal to gamma less than or equal to 35) has been studied with an applied magnetic field along the crystallographic c axis. For B greater than or similar to 1T, the glass. line is well described by the empirical relation B(g)=B(o)[(1 -T/T(c))/(T/T(c))](alpha), where alpha approximate to 1 and B(o) approximate to 1.85 Phi(o)/(gamma d)(2). The successful fit to this relation both below and above an alleged crossover in the solid vortex state has important consequences for the H-T phase diagram of high-temperature superconductors.
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| 6. |
- Lundqvist, Björn, et al.
(författare)
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Experimental evidence for a three-dimensional-two-dimensional crossover for magnetic fields parallel to the ab plane in oxygen-deficient single crystals of YBa2Cu3O7-delta
- 2000
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 62:5, s. 3542-3546
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Tidskriftsartikel (refereegranskat)abstract
- Resistive measurements on oxygen-deficient YBa2Cu3O7-delta single crystals of varying anisotropy gamma (22 less than or equal to gamma less than or equal to 36) have been used for investigations of the transition into a glassy vortex state for magnetic fields 0 less than or equal to B less than or equal to 12 T parallel to the ab plane. When B is accurately aligned parallel to the nb plane there is a remarkable change in behavior to a field-independent vortex solid-to-liquid transition at high magnetic fields. A possible explanation is suggested for the vertical transition involving a complete decoupling of the superconducting planes that leads to a two-dimensional system where the resistivity is given by nucleation of vortex-antivortex pairs.
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| 7. |
- Lundqvist, Björn, et al.
(författare)
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Field independent vortex solid-to-liquid transition for B parallel to ab in oxygen deficient single crystals of YBa(2)Cu(3)O(7-delta)
- 2000
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341:Part 3, s. 1335-1336
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of YBa(2)Cu(3)O(7-delta) provide a suitable test system for vortex dynamics in high temperature superconductors, since the electrical anisotropy gamma = (m(c)/m(ab))(1/2) can easily be varied over a large range by changing the oxygen content. In this paper the vortex solid-to-liquid transition, as determined from a vortex-glass analysis of the resistivity, has been studied for magnetic fields 012 T parallel with the ab plane of oxygen deficient single crystals of YBCO. Strikingly for high magnetic fields a field independent vortex solid-to-liquid transition is observed. A possible explanation for this phenomenon involving a crossover to a two-dimensional (2D) system is suggested.
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| 8. |
- 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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| 9. |
- Lundqvist, Björn, et al.
(författare)
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Vortex dynamics for in- and out-of-plane magnetic fields in oxygen deficient single crystals of YBa2Cu3O7-delta
- 2000
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284:Part. 1, s. 705-706
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Tidskriftsartikel (refereegranskat)abstract
- The resistive transition into a glassy vortex state in oxygen deficient single crystals of YBa2Cu3O7-delta (YBCO) has been studied for magnetic fields 0 less than or equal to B less than or equal to 12 T along the crystallographic c-axis, parallel to the ab plane, and also with a small misalignment of 1 degrees from the ab plane. Angular sweeps of the magnetic field reveal a sharp dip in the resistivity for B \textbackslash\textbackslash ab, which is attributed to intrinsic pinning of vortices between the planes. For Bile the vortex glass line is well described by B-g(T)= B-0[(1 - T/T-c)/(T/T-c)](alpha), where B-0 is anisotropy dependent and alpha approximate to 1.0-1.2. For B \textbackslash\textbackslash ab the behaviour is significantly different, and at high magnetic fields a change to a field-independent vortex solid-to-liquid transition is observed. This behaviour disappears for small misalignments between B and ab.
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| 10. |
- Lundqvist, Björn, et al.
(författare)
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Vortex dynamics in a thin film of Tl2Ba2CuO6
- 1999
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Ingår i: Journal of Low Temperature Physics. - 0022-2291 .- 1573-7357. ; 117:5-6, s. 1441-1445
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Tidskriftsartikel (refereegranskat)abstract
- The vortex dynamics in a Tl2Ba2CuO6 (Tl-2201) thin film with a critical temperature T-c = 80.8 K has been studied by electrical resistivity measurements for magnetic fields 0 less than or equal to B less than or equal to 12 T. The vortex glass line, as determined from the disappearance of linear resistivity, was found to be well described by B-g (T) = B-0[(1 - T/T-c)/(T/T-c)(alpha), with B-0 approximate to 0.65 T and alpha approximate to 1.9. The glass line of Tl-2201 is observed to be located below the one of Tl2Ba2CaCu2O8+delta (Tl-2212) in a magnetic phase diagram based on a reduced temperature scale T/T-c, thus suggesting a higher anisotropy for Tl-2201.
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