| 1. |
- Brisbois, J., et al.
(author)
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Flux penetration in a superconducting film partially capped with a conducting layer
- 2017
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 95:9
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Journal article (peer-reviewed)abstract
- The influence of a conducting layer on the magnetic flux penetration in a superconducting Nb film is studied by magneto-optical imaging. The metallic layer partially covering the superconductor provides an additional velocity-dependent damping mechanism for the flux motion that helps to protect the superconducting state when thermomagnetic instabilities develop. If the flux advances with a velocity slower than omega = 2/mu(0)sigma t, where sigma is the cap layer conductivity and t is its thickness, the flux penetration remains unaffected, whereas for incoming flux moving faster than w, the metallic layer becomes an active screening shield. When the metallic layer is replaced by a perfect conductor, it is expected that the flux braking effect will occur for all flux velocities. We investigate this effect by studying Nb samples with a thickness step. Some of the observed features, namely the deflection of the flux trajectories at the border of the thick center, as well as the favored flux penetration at the indentation, are reproduced by time-dependent Ginzburg-Landau simulations.
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| 2. |
- Cerbu, D., et al.
(author)
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Vortex ratchet induced by controlled edge roughness
- 2013
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15
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Journal article (peer-reviewed)abstract
- We demonstrate theoretically and experimentally the generation of rectified mean vortex displacement resulting from a controlled difference between the surface barriers at the opposite borders of a superconducting strip. Our investigation focuses on Al superconducting strips where, in one of the two sample borders, a saw tooth-like array of micro-indentations has been imprinted. The origin of the vortex ratchet effect is based on the fact that (i) the onset of vortex motion is mainly governed by the entrance/nucleation of vortices and (ii) the current lines bunching produced by the indentations facilitates the entrance/nucleation of vortices. Only for one current direction the indentations are positioned at the side of vortex entry and the onset of the resistive regime is lowered compared to the opposite current direction. This investigation points to the relevance of ubiquitous border effects typically neglected when interpreting vortex ratchet measurements on samples with arrays of local asymmetric pinning sites.
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| 3. |
- Motta, M., et al.
(author)
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Controllable morphology of flux avalanches in microstructured superconductors
- 2014
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 89:13
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Journal article (peer-reviewed)abstract
- The morphology of abrupt bursts of magnetic flux into superconducting films with engineered periodic pinning centers (antidots) has been investigated. Guided flux avalanches of thermomagnetic origin develop a treelike structure, with the main trunk perpendicular to the borders of the sample, while secondary branches follow well-defined directions determined by the geometrical details of the underlying periodic pinning landscape. Strikingly, we demonstrate that in a superconductor with relatively weak random pinning the morphology of such flux avalanches can be fully controlled by proper combinations of lattice symmetry and antidot geometry. Moreover, the resulting flux patterns can be reproduced, to the finest details, by simulations based on a phenomenological thermomagnetic model. In turn, this model can be used to predict such complex structures and to estimate physical variables of more difficult experimental access, such as the local values of temperature and electric field.
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| 4. |
- Motta, M., et al.
(author)
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Enhanced pinning in superconducting thin films with graded pinning landscapes
- 2013
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:21
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Journal article (peer-reviewed)abstract
- A graded distribution of antidots in superconducting a-Mo79Ge21 thin films has been investigated by magnetization and magneto-optical imaging measurements. The pinning landscape has maximum density at the sample border, decreasing linearly towards the center. Its overall performance is noticeably superior than that for a sample with uniformly distributed antidots: For high temperatures and low fields, the critical current is enhanced, whereas the region of thermomagnetic instabilities in the field-temperature diagram is significantly suppressed. These findings confirm the relevance of graded landscapes on the enhancement of pinning efficiency, as recently predicted by Misko and Nori.
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| 5. |
- Kupresak, Mario, et al.
(author)
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Nonlocal Hydrodynamic Response of Plasmonic Structures at Deep-nanometer Scale
- 2020
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In: Proceedings Elmar - International Symposium Electronics in Marine. - 1334-2630. ; 2020-September, s. 1-4
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Conference paper (peer-reviewed)abstract
- The electromagnetic properties of plasmonic nano-Antennas and scatterers with the characteristic dimensions at deep-nanometer scale, governed by quantum mechanical effects, have been extensively studied by a hydrodynamic approach. Several hydrodynamic models, together with additional boundary conditions, have been proposed to deal with the collective motion of the free electron gas in metals. In this work, four hydrodynamic models, namely the hard-wall hydrodynamic model, the curl-free hydrodynamic model, the shear forces hydrodynamic model, and the quantum hydrodynamic model are employed. The study is performed for a deep-nanometer metal core-dielectric shell sphere, excited by a plane wave. It is demonstrated that the far field characteristics of the core-shell nanosphere are largely affected by the choice of a specific hydrodynamic model.
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| 6. |
- Kupresak, Mario, et al.
(author)
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Nonlocal Response of Plasmonic Nanostructures Excited by Dipole Emitters
- 2021
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In: Proceedings Elmar - International Symposium Electronics in Marine. - 1334-2630. ; 2021-September, s. 25-28
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Conference paper (peer-reviewed)abstract
- The interaction between light and plasmonic structures at the deep-nanometer scale, which is essentially governed by nonclassical effects, has been increasingly investigated by the hydrodynamic model. Several hydrodynamic models have been introduced, in order to describe the motion of the free electron gas in metals. In this work, by employing the hard wall hydrodynamic model (HW-HDM) and the quantum hydrodynamic model (Q-HDM), the nonlocal response of an isolated metallic nanoparticle, excited by a dipole emitter, is investigated. The analysis is performed for the local density of states of an emitter coupled with a spherical nanoparticle, which may be treated analytically. Both radial and tangential emitters are studied, while varying the emitter-nanoparticle separation, and the nanoparticle's size and material. It is shown that HW-HDM and Q-HDM may generate striking spectral features, which do not arise within the classical approach.
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| 7. |
- Kupresak, Mario, et al.
(author)
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Hydrodynamic approach for deep-nanometer scale topologies: Analysis of metallic shell
- 2021
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In: 2020 International Symposium on Antennas and Propagation, ISAP 2020. ; , s. 269-270
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Conference paper (peer-reviewed)abstract
- In order to describe light-matter interaction at deep-nanometer scale, which is governed by nonclassical phenomena, a semiclassical hydrodynamic model with additional boundary conditions has been introduced. This model investigates the motion of the charged gas in metals, characterized by nonlocal material parameters. Based on different treatments of the nonlocality, several hydrodynamic models have been proposed. This work employs the hard wall hydrodynamic model (HW-HDM) and the quantum hydrodynamic model (Q-HDM). The study is performed for the mode structure (natural modes) of a spherical metallic nanoshell, supplemented by the plane wave response of the system. It is shown that the main transverse resonances of HW-HDM and Q-HDM experience nearly identical blueshifts in comparison to the classical resonances. The corresponding longitudinal resonances show noticeable spectrum shifts.
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