| 1. |
- Ao, Ping, et al.
(författare)
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Vortex dynamics within the BCS theory
- 1997
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Ingår i: Physica. C, Superconductivity. - : Elsevier. - 0921-4534 .- 1873-2143. ; 282-287:Part 1, s. 367-370
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Tidskriftsartikel (refereegranskat)abstract
- Based on the BCS theory we outline a conventional path integral derivation of the transverse force and the friction for a vortex in a superconductor. The derivation is valid in both clean and dirty limits at both zero and finite temperatures. The transverse force is found to be precisely as what has been obtained by Ao and Thouless using the Berry's phase method. The friction is essentially the same as the Bardeen and Stephen's result.
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| 2. |
- Grivel, Jean-Claude, et al.
(författare)
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First-order melting transition observed from resistivity measurements in ultra-pure YBa2Cu3O7-delta single crystals with high twin boundary density
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 322:3-4, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- R(T) measurements have been performed on optimally and overdoped heavily twinned high-purity YBa2Cu3O7-delta single crystals, under a magnetic field B oriented parallel to the twin boundary planes (B parallel to c). The characteristic feature attributed to the flux line lattice melting transition has been observed in the overdoped case for B greater than or equal to 5 T. The first-order transition was not found in the optimally doped sample, even when B was tilted with respect to the c-axis. Differences between these samples are discussed.
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| 3. |
- Hu, Q H, et al.
(författare)
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Properties of Tl-2201 thin films
- 1997
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 282-287:Part 2, s. 1075-1076
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Tidskriftsartikel (refereegranskat)abstract
- Tl2Ba2CuO6 (Tl-2201) thin films were synthesised on single crystal LaAlO3 and SrTiO3 substrates and on bicrystal LaAlO3 by an ex-situ process. Depending on thallium content and processing conditions, the films were orthorhombic or tetragonal. Tc was in the range 30 – 92 K while Jc reached 4.106A/cm2 at 12 K. By oxygen depletion, Tc was increased by 15 – 20 K for some films.
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| 4. |
- Istomin, Sergey Ya., et al.
(författare)
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A new superconducting sulfide—'EuNb2S5'
- 1998
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Ingår i: Physica. C, Superconductivity. - : Elsewier. - 0921-4534 .- 1873-2143. ; 300, s. 67-70
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Tidskriftsartikel (refereegranskat)abstract
- A new low-temperature superconducting (Tc≈3 K) niobium sulfide ‘EuNb2S5' with a hexagonal structure (a=3.3556(8) Å, c=23.440(9) Å) was synthesized from a mixture of EuS, Nb(m) and S in evacuated and sealed silica tubes, heated at 1100°C for 48 h. This superconductor was characterized by EDX analysis, X-ray powder and electron diffraction studies. Electron diffraction revealed the presence of a supercell: asuper=bsuper=√7×a.
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| 5. |
- Jukna, A, et al.
(författare)
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Electric properties of planar Ag/HgBa2CaCu2O6+delta interface
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 316:1-2, s. 83-88
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Tidskriftsartikel (refereegranskat)abstract
- Silver coatings were magnetron sputtered onto the surface of highly c-axis-oriented HgBa2CaCu2O6+delta superconducting thin films exhibiting zero resistance T-c at about 120 K and the critical current density similar to 10(5) A/cm(2) at 100 K. Electrical resistance of the Ag/HgBa2CaCu2O6+delta planar interface and current-voltage dependencies were investigated in a course of post-deposition annealing of the Ag/HgBa2CaCu2O6+delta at 50-350 degrees C in both purl oxygen and oxygen-free ambient. Results of the electrical measurements are explained in terms of the insulating layer formation at the Ag/HgBa2CaCu2O6+delta interface. It is assumed this insulator is a product created by oxygen non-stoichiometry and decomposition of the superconductor at the interface between both materials. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 6. |
- Langmann, Edwin, et al.
(författare)
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Mean field analysis of a model for superconductivity in an anti-ferromagnetic background
- 1998
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Ingår i: Physica. C, Superconductivity. - : Elsevier. - 0921-4534 .- 1873-2143. ; 296:1-2, s. 119-136
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Tidskriftsartikel (refereegranskat)abstract
- We study a lattice fermion model for superconductivity in the presence of an anti-ferromagnetic background, described as a fixed external staggered magnetic field. We discuss the possibility that our model provides an effective description of coexistence of anti-ferromagnetic correlations and superconductivity, and its possible application to high-temperature superconductivity. We also argue that, under certain conditions, this model describes a variant of the periodic Anderson model for heavy fermions. Using a path integral formulation we construct mean field equations, which we study in some detail. We evaluate the superconducting critical temperature and show that it is strongly enhanced by anti-ferromagnetic order. We also evaluate the superconducting gap, the superconducting density of states, and the tunneling conductivity, and show that the most stable channel usually has a dx2-y2-wave gap.
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| 7. |
- Lundqvist, Björn, et al.
(författare)
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Vortex dynamics in oxygen deficient single crystals of YBa2Cu3O7-delta
- 1997
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 282, s. 1959-1960
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Tidskriftsartikel (refereegranskat)abstract
- In YBa2Cu3O7-delta (YBCO), oxygen deficiencies in the CuO chains change the coupling between the charge carriers in adjacent superconducting CuO2 planes and thereby the electrical anisotropy, gamma=(m(c)/m(ab))(1/2). Such crystals therefore provide a simple test system for systematic studies of the influence of anisotropy on vortex dynamics. We have studied the vortex glass transition of YBCO single crystals with delta in the range of 0.07 to 0.27, corresponding to gamma between 9 and 18, for magnetic fields 0
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| 8. |
- Qvarford, M., et al.
(författare)
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X-ray absorption study of oxygen in the high-Tc superconductor Bi2Sr2CaCu2O8 near the interfaces to Cu, Ag and Au
- 1996
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 265:1-2, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- The influence on O 2p holes in single crystalline Bi2Sr2CaCu2O8 upon the interface formation to Cu, Ag and Au has been studied by O K edge X-ray absorption measurements. It was found that Cu reduces the amount of doping induced O 2p holes significantly in the vicinity of the interface, whereas Ag and Au gave a much smaller reduction of these states. Photoemission spectra confirmed previous findings that Cu causes a strong chemical reaction at the Bi-O surface of Bi2Sr2CaCu2O8, in contrast to Ag and Au which induced only a minimal reaction. The results support the opinion that the Bi-O layers are essential for the doping of the Cu-O2 layers in Bi2Sr2CaCu2O8.
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| 9. |
- Kakihana, M., et al.
(författare)
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A simple and reproducible way to synthesize PrBa2Cu4O8 under 1 atm of oxygen by amorphous citrate method
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 321, s. 74-80
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Tidskriftsartikel (refereegranskat)abstract
- A simple aqueous solution technique utilizing citric acid (CA) as a complexant was applied to prepare PrBa2Cu4O8 (Pr124) at ambient oxygen pressure. Heating of a mixed-solution of CA, water (H2O) and ions of Pr, Ba and Cu with a molar ratio of [CA]:[H2O]:[Pr + Ba + Cu] = 3.6:40:1 on a hot-plate set at 200 degrees C produced a transparent amorphous citrate "gel" without any precipitation, which after heat-treatment at 450 degrees C was converted to a precursor for Pr124. The Pr124 compound with only minor traces of BaCuO2, PrBaO3 and CuO formed after heat-treating the precursor twice at 850 degrees C for 60 h under 1 atm oxygen pressure. The amount of impurities in the citrate-derived Pr124 was approximately half of that in the best sample previously prepared by the more elaborate high-pressure technique. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 10. |
- Chakalov, R, et al.
(författare)
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Fabrication and investigation of YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 thin film structures for voltage tunable devices
- 1998
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Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 308:3-4, s. 279-288
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature superconducting/ferroelectric thin film structures were deposited by laser ablation. Three types of voltage tunable devices were fabricated and investigated-trilayer capacitor, planar interdigital capacitor and coplanar waveguide. As ferroelectric the solid solution BaxSr1-xTiO3 was chosen with barium content x = 0.05 because its Curie temperature is close to the liquid nitrogen boiling point (77 K). Temperature and voltage dependences of the Ba0.05Sr0.95TiO3 dielectric constant epsilon(r,BSTO) were studied. High epsilon(r,BSTO) values were determined-up to 3000 at 75 K, 20 GHz and zero de bias. Efficient voltage tunability was demonstrated (up to 40%) at loss level tan delta=0.01-0.1. Compact YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 coplanar waveguide with as narrow gap as 18 mu m was tested as electrically tunable phase-shifter and field-induced phase shifts of more than 180 degrees were obtained by 35 V de bias at 20 GHz. This improvement was attained by proper choice of the ferroelectric material, accomplished epitaxial growth of the films and decrease of the specific dimensions. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
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