| 1. |
- Espinosa-Arronte, Beatriz, et al.
(författare)
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Scaling of the B-dependent resistivity for different orientations in Fe doped YBa2Cu3O7-[delta]
- 2005
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 423:1-2, s. 69-73
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Tidskriftsartikel (refereegranskat)abstract
- The angular dependence of a previously proposed modified model of the vortex glass transition has been investigated. The in-plane resistivity in an optimally oxygen doped YBa2Cu3O7-delta single crystal, doped with 1% Fe, was measured in fields up to 12 T applied with different orientations with respect to the crystallographic c-axis. The transition curves at all orientations were successfully scaled into one curve according to a scaling variable for the normalized resistivity. Characteristic parameters of the model, like the glass transition temperature and the magnetic field B-0, were measured at each orientation and were in good agreement with the expected values. These results show that the model proposed is valid also for fields applied outside the c-axis, giving further support to a more consistent description of the vortex liquid resistivity.
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| 2. |
- Gardchareon, A, et al.
(författare)
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Anisotropic properties of spherical single crystals of La1.8Sr0.2CuO4-delta
- 2006
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 439:2, s. 85-92
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of La1.8Sr0.2CuO4-delta grown by the traveling solvent floating zone method have been ground to spherical shape for studies of anisotropic superconducting properties by SQUID magnetometry. At low enough temperatures and fields, the spheres are perfectly shielding (susceptibility -1.5 [SI]) and thus magnetically isotropic. The field dependence of the critical temperature, the transition width and the field expulsion well below T-c of the two crystals is detailed in this paper. The anisotropy of the first critical field when the applied field is parallel and perpendicular to the c-axis of the crystals amounts to about 3 and is within errorbars independent of temperature for both samples. Magnetization vs. field experiments along principal and intermediate field directions demonstrate the angular dependence of the hysteresis.
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| 3. |
- Ghorbani, S. R., et al.
(författare)
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The normal state Hall effect in Nd1-2xCaxMxBa2Cu3O7-delta (M = Pr, Th) : Evidence for hole localization by disorder
- 2005
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 424:04-mar, s. 159-168
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Tidskriftsartikel (refereegranskat)abstract
- The transport properties of sintered samples of Nd1-2xCaxMxBa2Cu3O7-delta (M = Pr, Th) with 0 <= x <= 0.10 have been studied in the normal state by Hall effect measurements. The Hall coefficient at high temperature was almost constant for Ca-Pr while it increased with increasing Ca-Th doping concentration. The results for the Hall coefficient as a function of temperature and doping concentration were analyzed within two different models. A good agreement between models and data was obtained. On the basis of these models, it was inferred that Ca-Pr and Ca-Th doping introduce electronic disorder in the CUO2 planes. The localization tendency is driven by electronic disorder. This is the main reason for strong depression of the superconducting critical temperature in both alloys. It was found that the Hall angle is proportional to T-2 in the whole measured temperature range in Ca-Pr doped samples while there are deviations at high temperature in the Ca-Th doped series. In a phenomenological narrow band model, the conduction band was asymmetric for the pure sample and this asymmetry decreased with increasing Ca-Th doping while it was almost constant for Ca-Pr doped samples.
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| 4. |
- Khmelevskuyi, S., et al.
(författare)
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Frustrated magnetism in superconducting hexagonal Fe : Calculation of inter-atomic pair exchange interactions
- 2007
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 460, s. 647-648
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Tidskriftsartikel (refereegranskat)abstract
- We calculate magnetic exchange interaction parameters in hcp Fe using magnetic force theorem in density functional theory in a range of volumes, which covers the region of stability of the superconducting state. The calculations are done for a paramagnetic state using disordered local moment model within a local fixed spin-moment constraint. It is found that exchange interaction parameters strongly favor antiferromagnetic inter-plane stacking of the basal hcp planes. At the same time, the nearest neighbor in-plane exchange interaction parameters are also strongly antiferromagnetic, which should lead to magnetic frustrations in the planar triangular lattice. Eventual consequences of the magnetic frustration effects on the interplay between magnetism and superconductivity in hcp Fe under pressure are discussed.
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| 5. |
- Bauch, Thilo, 1972, et al.
(författare)
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YBCOSQUIDs with unconventional current phase relation
- 2007
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 463-465:1 October 2007, s. 979-984
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the dynamics of YBa2Cu3O7-delta,5 (YBCO) dc sperconducting quantum interference devices (SQUIDs) characterized by an unconventional Josephson current phase relation (CPR). We have focused on SQUID configurations with Josephson junctions where the lobe of the order parameter in one electrode is facing a node in the other electrode. This order parameter arrangement should enhance the appearance of a sin(2(p) term in the CPR. The response of the critical current of the dc SQUID, under the effect of an external magnetic field, has been measured in temperature, down to 20 mK. Our experimental data have been compared with numerical simulations of the SQUIDs dynamics by considering a CPR of a single junction of the form I(phi) = I-I sin(phi) - I-II sin(2 phi) where I-I, and I-II are, respectively, the first and second harmonic component. In our devices the values of the sin(2 phi) term are such that the fundamental state of the SQUID is naturally double degenerate. This is of great relevance for applications of d-wave SQUIDs in quantum information processing. (C) 2007 Elsevier B.V. All rights reserved.
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| 6. |
- Gustafsson, David, 1982, et al.
(författare)
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Low capacitance HTS junctions for single electron transistors
- 2009
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 470:SUPPL.1, s. S188-S190
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Konferensbidrag (refereegranskat)abstract
- We have fabricated and characterized YBa2Cu3O7-δ grain boundary junctions to determine their feasibility as tunnel barriers in single electron transistors. Superconducting quantum interference devices with injection lines have been used to measure the junctions capacitance. We have extracted capacitance values which allow us to achieve a Coulomb blockade regime for sufficiently small junction dimensions.
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| 7. |
- Kawabata, Shiro, et al.
(författare)
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Cooper pair transport and macroscopic quantum dynamics in Josephson junctions through ferromagnetic insulators
- 2008
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 468:7-10, s. 701-704
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically investigate the cooper pair transport and the macroscopic quantum dynamics of a Josephson junction with a superconductor (S) and a ferromagnetic insulator (FI). By use of the recursive Green's function method, we numerically found the formation of the pi junction in the case of the fully spin-polarized FI. On the other hand, the Josephson current through the spin filtering barrier does not show the pi junction behaviors. By deriving the effective action from microscopic Hamiltonian, a pi junction flux qubit is proposed. In this qubit, a quantum two-level system is spontaneously generated and the effect of the quasiparticle dissipation is found to be very weak.. These features make it possible to realize a quiet qubit with high coherency.
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| 8. |
- Kornev, V. K., et al.
(författare)
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Dynamics of underdamped Josephson junctions with non-sinusoidal current-phase relation
- 2006
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 435:1-2, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Results on analytical and computational investigations of high-frequency dynamics of Josephson junctions, characterized by non-zero capacitance and the second harmonic in the current-phase relation are presented. These attributes each have influence on the behaviour of integer Shapiro steps and lead to the formation of non-integer Shapiro steps. Analytic theory of the integer and non-integer Shapiro steps has been developed for the so-called high-frequency limit. The analytical and numerical results are compared with experimental data for hybrid heterostructures YBCO/Au/Nb. Detector response for the case of high fluctuation level has been considered as well.
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| 9. |
- Kuzmin, Leonid, 1946
(författare)
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Ultra-sensitive cryogenic thermometer based on an array of the SIN tunnel junctions
- 2008
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 468:3, s. 142-146
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Tidskriftsartikel (refereegranskat)abstract
- A novel concept of an ultra-sensitive thermometer based on a series array of superconductor-insulator-normal (SIN) tunnel junctions has been proposed. The array helps to improve matching with an amplifier proportionally to the number of junctions. There is no fundamental limit for total noise and the main limitation is electron-phonon noise of the normal island reverse proportional to volume of the normal metal. (c) 2007 Elsevier B.V. All rights reserved.
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| 10. |
- Larsson, Sven, 1941
(författare)
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Strong electron correlation and phonon coupling in high T-c superconductors
- 2007
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 460, s. 1063-1065
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Tidskriftsartikel (refereegranskat)abstract
- Systems with one active electron (or hole) per site may be spin-alternating (SDW) or charge alternating (CDW). Typical SDW systems (CuO) cannot be described with a single Slater determinant. Electron correlation is also important in typical CDW systems such as BaBiO3 (on-site correlation). If the CDW and the SDW phases have similar free energies, they are either connected by a phase transition, or, if the zero-point vibrations overlap sufficiently, mix quantum mechanically and form a new phase. It will be shown, using very accurate quantum chemical calculations that a four-site Cu-O cluster has local energy minima for both phases. The properties of the mixed phase are those of a superconductor: The electrons are coupled in pairs, move in a delocalized non-activated way, and give a current in a magnetic field equivalent to the Meissner effect. (c) 2007 Elsevier B.V. All rights reserved.
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