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1
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Fracton Contribution to the Electron and Magnon Pairing

100%
Bąk Z.
|
|
vol. 126
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issue 1
372-373
EN
We show that high temperature superconductivity contrary to the Bardeen-Cooper-Schrieffer /BCS/ superconductors exhibits three important energy scales. The highest is associated with the formation of Cooper pairs coupled due to the magnetic fracton excitations, the second (pseudogap) we ascribe to the formation of coherent but not nonsuperfluid condensate. The lowest energy scale (superconducting gap) we associate with the onset of superfluidity of the condensate that is due to the phonon aided fracton hopping.
2
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Heavy Fermion Superconductor Order Parameter in High Magnetic Field

100%
Kowalewski L., Wojciechowski R., Thomas M., Nogala M.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
347-350
EN
It is shown that, independently on either the nature and the strength of pairing, the orbital effects of a high magnetic field in heavy fermion superconductor change the form of both the effective pairing and the gap function.
3
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Pairing Correlations around Negative-U Centre in the Two-Band Model

100%
Ciechan A., Wysokiński K.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
123-127
EN
The electron energy spectrum of many superconducting materials is characterised by the presence of few bands at the Fermi level. In some cases the superconducting properties seem to be dominated by single band but in others the many-band approach is essential ingredient of their description. In this paper we shall study the properties of superconducting impurity placed in a non-superconducting medium. We are interested in the evolution of superconducting correlations within non-superconducting 1- or 2-dimensional system, their dependence on the distance from impurity and changes induced by the presence of the second band and interband scattering. We use real space description of the material and Bogolyubov-de Gennes approach to superconductivity.
4
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Finite Size Corrections in the Two-Level BCS Model

100%
Ciechan A., Wysokiński K.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
569-572
EN
Superconducting properties of small metallic grains modelled by highly degenerate two-level spectrum have been studied. We have solved numerically Richardson's exact equations for the system of 2N electrons in two levels. Characterising the size of the grain by the level degeneracy we study the finite size corrections to the thermodynamic limit of the ground and lowest excited state energy. The interparticle distance∝ N^{-1/3} seems to be the expansion parameter. The obtained results have been compared with those of other authors.
5
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Thermodynamics of the Two-Level Richardson Model

100%
Ciechan A., Wysokiński K.
Acta Physica Polonica A
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2007
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vol. 111
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issue 4
467-473
EN
The two-level version of the Richardson model presents a unique possibility to calculate numerically exactly thermodynamic properties of the system it describes. The point is that all energies and the degeneracies of the many-body system can be easily calculated. The energies are given by the eigenvalues of the small (of order of N×N, where 2N is a number of electrons in the system) tridiagonal matrices. Here we numerically obtain a complete spectrum of the interacting two-level model and calculate the specific heat and the pairing energy of the small system at finite temperatures.
6
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Magnetic Properties of Milled and Thermal Relaxed YBa_{2} (Cu_{1-x}Fe_{x})_{3}O_{y}

100%
Timko M., Kováč J., Sargánková I., Zentková M., Mihalik M., Maťaš S., Čiasnohová A.
Acta Physica Polonica A
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1997
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vol. 91
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issue 2
355-358
EN
The influence of the mechanical milling and subsequent thermal relaxation on magnetic and superconducting behaviour of YBa_{2}(Cu_{1-x}Fe _{x})_{3}O_{y} system has been studied. Two methods of heat treatment were used: Set I - slow cooling from 980°C in flowing O_{2} and Set II - reducing at 770°C in flowing Ar_{2} followed by reoxidation in flowing O_{2} below 400°C. The transition to superconductivity, diamagnetic response, critical current density and the effective magnetic moment in the normal state have been estimated. Our measurements indicate that the reducing atmosphere preparation is less detrimental on superconducting properties. The results are discussed in terms of occupancy Cu sites by Fe and redistribution of oxygen atoms.
7
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Fault Current Limitation by 2G HTS Superconducting Transformer - Experimental Investigation

75%
Wojtasiewicz G.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
516-520
EN
Transformers represent one of the oldest and most mature elements in a power transmission and distribution network. The new superconducting transformers are smaller and lighter than conventional ones and they have lower power losses, too. Also, the new 2G superconducting tapes with high resistivity in the normal state allow to build transformers with high short-circuit strength. The short-circuit current limiting feature of the superconducting transformer, which is the most important benefit of replacing conventional windings by superconducting ones, provides protection and significantly reduces the wear and tear of circuit breakers and other substation power equipment. This paper describes the design and experimental investigations results of a model of a 1-phase, 8.8 kVA superconducting transformer with windings made of 2G HTS tape. A special regard is given to the ability of the device's superconducting winding to limit the short-circuit current, in particular its equivalent resistance in normal state at a temperature of 77 K (i.e. resistance of the resistive layers of the HTS tape just after transition to the non-superconducting state).
8
Content available remote

Superconducting Devices for Power Engineering

63%
Janowski T., Kondratowicz-Kucewicz B., Wojtasiewicz G., Kozak S., Kozak J., Majka M., Jaroszyński L.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
537-544
EN
The paper presents the current state of research on superconducting devices for the electrical power system, i.e. transformers, fault-current limiters, and energy storages. In particular, it describes scientific achievements of the Laboratory of Superconducting Technologies of Electrotechnical Institute. The development of distributed and renewable energy sources, as well as the increasing number of receivers with low power factor will rise interest in superconducting fault-current limiters and superconducting transformers rated below 1 MVA. Previous studies were focused on the largest power transformers and highest current superconducting fault-current limiters. ReBCO coated conductors allow to build efficient superconducting AC devices. Superconducting tape of a layered structure (second generation HTS tape) enables the construction of transformer rated up to a few MVA without the usage of parallel conductors. Relatively high resistance of the tape in normal state allows to build fault-current limiters and fault-current limiting transformers. Superconducting transformers and superconducting fault-current limiters can help to increase connected power of distribution stations and thereby accelerate development of renewable energy sources.
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