| 1. |
- Babaev, Egor, et al.
(författare)
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Type-1.5 superconductivity in multiband systems : Magnetic response, broken symmetries and microscopic theory - A brief overview
- 2012
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 479, s. 2-14
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Tidskriftsartikel (refereegranskat)abstract
- A conventional superconductor is described by a single complex order parameter field which has two fundamental length scales, the magnetic field penetration depth lambda and the coherence length xi. Their ratio kappa determines the response of a superconductor to an external field, sorting them into two categories as follows; type-I when kappa < 1/root 2 and type-II when kappa > 1/root 2. We overview here multicomponent systems which can possess three or more fundamental length scales and allow a separate "type-1.5" superconducting state when, e. g. in two-component case xi(1) < root 2 lambda < xi(2). In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges. As a consequence the system should form an additional Semi-Meissner state which properties we discuss below. In that state vortices form clusters in low magnetic fields. Inside the cluster one of the component is depleted and the superconductor-to-normal interface has negative energy. In contrast the current in second component is mostly concentrated on the cluster's boundary, making the energy of this interface positive. Here we briefly overview recent developments in Ginzburg-Landau and microscopic descriptions of this state.
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| 2. |
- Babaev, Egor, et al.
(författare)
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Type-1.5 superconductivity in two-band systems
- 2010
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 470:19, s. 717-721
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Tidskriftsartikel (refereegranskat)abstract
- In the usual Ginzburg-Landau theory the critical value of Ginzburg-Landau parameter kappa(c) = 1/root 2 separates regimes of type-I and type-II superconductivity. The latter regime possess thermodynamically stable vortex excitations which interact with each other repulsively and tend to form vortex lattices. It was shown in [5] that this dichotomy in broken in U(1) x U(1) Ginzburg-Landau models which possess a distinct phase with vortex excitations which interact attractively at large length scales and repulsively at shorter distances. Here we discuss the influence of the Josephson coupling and that similar kind of superconductivity can also arise for entirely different reasons in superconductors where only one band is superconducting if this band interacting via a proximity effect with another band (the report is partially based on [1]).
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| 3. |
- Edström, Alexander
(författare)
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Three and four-body intervortex forces in the Ginzburg-Landau model of single- and multicomponent superconductivity
- 2013
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 487, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- A systematic numerical study of non-pairwise vortex interaction forces in the Ginzburg-Landau model for single-and multicomponent superconductivity is presented. The interactions are obtained by highly accurate numerical free energy minimization. In particular a three-body interaction is defined as the difference between the total interaction and sum of pairwise interactions in a system of three vortices and such interactions are studied for single and two-component type-1, type-2, and type-1.5 superconductors. In the investigated regimes, the three-body inter action is found to be short-range repulsive but long-range attractive in the type-1 case, zero in the critical kappa (Bogomoln'y) case, attractive in the type-2 case and repulsive in the type-1.5 case. Some systems of four vortices are also studied and results indicate that four-body forces are of substantially less significance than the three-body interactions.
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| 4. |
- Fiolhais, Miguel C. N., et al.
(författare)
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Magnetic field expulsion from an infinite cylindrical superconductor
- 2014
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 497, s. 54-57
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Tidskriftsartikel (refereegranskat)abstract
- The solutions of the London equations for the magnetic field expulsion from superconductors are presented in this paper for the cylindrical symmetry. The result is analyzed in detail and represented numerically for the case of a uniform external magnetic field in the transverse plane. In particular, several contour plots of the magnetic energy density are depicted for the regions inside and around the superconducting area for a wide range of penetration lengths, showing how the expulsion and penetration of the magnetic field evolve with the ratio between the penetration length and the cylinder radius.
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| 5. |
- Freelon, B., et al.
(författare)
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Low energy electronic spectroscopy of an infinite-layer cuprate : A resonant inelastic X-ray scattering study of CaCuO2
- 2010
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 470:3, s. 187-192
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of Oxygen K-edge soft X-ray absorption and emission spectroscopy that was performed on an infinite-layer insulating cuprate thin film CaCuO2 Experimentally obtained spectra arc consistent with local density approximation calculations X-ray absorption spectra show a close resemblance to spectra obtained from homologous single crystal cuprates In addition to d-d excitations. X-ray emission spectra reveal the presence of Zhang-Rice singlet states in the infinite-layer CuO2 planes The question of whether the Zhang-Rice singlet features are masked by the O 2p main-band is addressed. it is possible to quantify the position of the Zhang-Rice singlet using emission intensity profiles X-ray emission is demonstrated as a tool for understanding CuO2 planar electronic correlation in the prototypical infinite-layer The energy difference, 2 0 eV, between the oxygen main-band and the Zhang-Rice singlet band is found to match values obtained theoretically using established planar electronic correlation parameters.
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| 6. |
- Golod, Taras, et al.
(författare)
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Application of nano-scale Josephson junction as phase sensitive detector for analysis of vortex states in mesoscopic superconductors
- 2010
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 570:19, s. 890-892
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Tidskriftsartikel (refereegranskat)abstract
- We study phase shifts in a Josephson junction induced by vortices in superconducting mesoscopic electrodes. The position of the vortices are controlled by suitable geometry of a nano-scale Nb–Pt1−xNix–Nb junction of the overlap type made by Focused Ion Beam (FIB) sculpturing. The vortex is kept outside the junction, parallel to the junction plane. From the measured Fraunhofer characteristics the entrance and exit of vortices are detected. By changing the bias current through the junction at constant magnetic field the vortices can be manipulated and the system can be switched between two consecutive vortex states which are characterized by different critical currents of the junction. A mesoscopic superconductor thus acts as a non-volatile memory cell in which the junction is used both for reading and writing information (vortex). Furthermore, we observe that the critical current density of Nb–Pt1−xNix–Nb junctions decreases non-monotonously with increasing Ni concentration. It exhibits a minimum at 40 at.% Ni, which is an indication of switching into the π state.
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| 7. |
- Motzkau, Holger, 1985-, et al.
(författare)
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Strong polaritonic interaction between flux-flow and phonon resonances in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions : Angular dependence and the alignment procedure
- 2013
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 491, s. 51-55
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Tidskriftsartikel (refereegranskat)abstract
- Bi2Sr2CaCu2O8+x single crystals represent natural stacks of atomic scale intrinsic Josephson junctions, formed between metallic CuO2–Ca–CuO2 and ionic insulating SrO–2BiO–SrO layers. Electrostriction effect in the insulating layers leads to excitation of c-axis phonons by the ac-Josephson effect. Here we study experimentally the interplay between and velocity matching (Eck) electromagnetic resonances in the flux-flow state of small mesa structures with c-axis optical phonons. A very strong interaction is reported, which leads to formation of phonon-polaritons with infrared and Raman-active transverse optical phonons. A special focus in this work is made on analysis of the angular dependence of the resonances. We describe an accurate sample alignment procedure that prevents intrusion of Abrikosov vortices in fields up to 17 T, which is essential for achieving high-quality resonances at record high frequencies up to 13 THz.
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| 8. |
- Ögren, Magnus, 1977-, et al.
(författare)
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Self-consistent Ginzburg-Landau theory for transport currents in superconductors
- 2012
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Ingår i: Physica. C, Superconductivity. - : Elsevier. - 0921-4534 .- 1873-2143. ; 479, s. 157-159
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Tidskriftsartikel (refereegranskat)abstract
- We elaborate on boundary conditions for Ginzburg-Landau (GL) theory in the case of external currents. We implement a self-consistent theory within the finite element method (FEM) and present numerical results for a two-dimensional rectangular geometry. We emphasize that our approach can in principle also be used for general geometries in three-dimensional superconductors. © 2012 Elsevier B.V. All rights reserved.
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| 9. |
- Anders, S., et al.
(författare)
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European roadmap on superconductive electronics - Status and perspectives
- 2010
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 470:23-24, s. 2079-2126
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Tidskriftsartikel (refereegranskat)abstract
- For four decades semiconductor electronics has followed Moore's law: with each generation of integration the circuit features became smaller, more complex and faster. This development is now reaching a wall so that smaller is no longer any faster. The clock rate has saturated at about 3-5 GHz and the parallel processor approach will soon reach its limit. The prime reason for the limitation the semiconductor electronics experiences is not the switching speed of the individual transistor, but its power dissipation and thus heat. Digital superconductive electronics is a circuit- and device-technology that is inherently faster at much less power dissipation than semiconductor electronics. It makes use of superconductors and Josephson junctions as circuit elements, which can provide extremely fast digital devices in a frequency range - dependent on the material - of hundreds of GHz: for example a flip-flop has been demonstrated that operated at 750 GHz. This digital technique is scalable and follows similar design rules as semiconductor devices. Its very low power dissipation of only 0.1 mu W per gate at 100 GHz opens the possibility of three-dimensional integration. Circuits like microprocessors and analogue-to-digital converters for commercial and military applications have been demonstrated. In contrast to semiconductor circuits, the operation of superconducting circuits is based on naturally standardized digital pulses the area of which is exactly the flux quantum Phi(0). The flux quantum is also the natural quantization unit for digital-to-analogue and analogue-to-digital converters. The latter application is so precise, that it is being used as voltage standard and that the physical unit 'Volt' is defined by means of this standard. Apart from its outstanding features for digital electronics, superconductive electronics provides also the most sensitive sensor for magnetic fields: the Superconducting Quantum Interference Device (SQUID). Amongst many other applications SQUIDs are used as sensors for magnetic heart and brain signals in medical applications, as sensor for geological surveying and food-processing and for non-destructive testing. As amplifiers of electrical signals. SQUIDs can nearly reach the theoretical limit given by Quantum Mechanics. A further important field of application is the detection of very weak signals by 'transition-edge' bolo-meters, superconducting nanowire single-photon detectors, and superconductive tunnel junctions. Their application as radiation detectors in a wide frequency range, from microwaves to X-rays is now standard. The very low losses of superconductors have led to commercial microwave filter designs that are now widely used in the USA in base stations for cellular phones and in military communication applications. The number of demonstrated applications is continuously increasing and there is no area in professional electronics, in which superconductive electronics cannot be applied and surpasses the performance of classical devices. Superconductive electronics has to be cooled to very low temperatures. Whereas this was a bottleneck in the past, cooling techniques have made a huge step forward in recent years: very compact systems with high reliability and a wide range of cooling power are available commercially, from microcoolers of match-box size with milli-Watt cooling power to high-reliability coolers of many Watts of cooling power for satellite applications. Superconductive electronics will not replace semiconductor electronics and similar room-temperature techniques in standard applications, but for those applications which require very high speed, low-power consumption, extreme sensitivity or extremely high precision, superconductive electronics is superior to all other available techniques. To strengthen the European competitiveness in superconductor electronics research projects have to be set-up in the following field: - Ultra-sensitive sensing and imaging. - Quantum measurement instrumentation. - Advanced analogue-to-digital converters. - Superconductive electronics technology.
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| 10. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Resistive state triggered by vortex entry in YBa2Cu3O7-delta nanostructures
- 2014
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 506, s. 165-168
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Tidskriftsartikel (refereegranskat)abstract
- We have realized YBa2Cu3O7-delta nanowires and nano Superconducting Quantum Interference Devices (nanoSQUID). The measured temperature dependence of the wire resistances below the superconducting transition temperature has been analyzed using a thermally activated vortex entry model valid for wires wider than the superconducting coherence length. The extracted zero temperature values of the London penetration depth, lambda(0) similar or equal to 270 +/- 15 nm, are in good agreement with the value obtained from critical current modulations as a function of an externally applied magnetic field in a nanoSQUID implementing two nanowires.
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