References of "Silhanek, Alejandro"
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See detailFirst vortex entry into a perpendicularly magnetized superconducting thin film
Gutierrrez, Joffre; Raes, Bart; Van de Vondel, Joris et al

in Physical Review. B : Condensed Matter (2013), 88

In type-II superconductors, the flux-free state (Meissner state) may be invaded by vortices bearing quantized flux once H is above the lower critical field Hc1. However, the actual first flux penetration ... [more ▼]

In type-II superconductors, the flux-free state (Meissner state) may be invaded by vortices bearing quantized flux once H is above the lower critical field Hc1. However, the actual first flux penetration does not occur at Hc1 due to the presence of a surface barrier and the fact that the Meissner state may also exist as a metastable state up to a larger (superheating) field. In this work we determine the field for the first vortex penetration in superconductors, by directly imaging the first vortex threading a superconducting Pb film with antidots. We find that the first vortex penetration occurs when the surface superconducting currents reach the depairing current, locally breaking superconductivity and allowing a vortex to nucleate. [less ▲]

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See detailQuantifying the sorting efficiency of self-propelled run-and-tumble swimmers by geometrical ratchets
Berdakin; Silhanek, Alejandro ULg; Moyano Cortéz, H. N. et al

in Central European Journal of Physics (2013)

Suitable asymmetric microstructures can be used to control the direction of motion in microorganism populations. This rectification process makes it possible to accumulate swimmers in a region of space or ... [more ▼]

Suitable asymmetric microstructures can be used to control the direction of motion in microorganism populations. This rectification process makes it possible to accumulate swimmers in a region of space or to sort different swimmers. Here we study numerically how the separation process depends on the specific motility strategies of the microorganisms involved. Crucial properties such as the separation effi ciency and the separation time for two bacterial strains are precisely defined and evaluated. In particular, the sorting of two bacterial populations inoculated in a box consisting of a series of chambers separated by columns of asymmetric obstacles is investigated. We show how the sorting e fficiency is enhanced by these obstacles and conclude that this kind of sorting can be effi ciently used even when the involved populations differ only in one aspect of their swimming strategy. [less ▲]

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See detailMapping Magnetic Near-Field Distributions of Plasmonic Nanoantennas
Denkova, D; Verellen, N; Silhanek, Alejandro ULg et al

in ACS Nano (2013)

We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning nearfield optical microscopy (SNOM). By means of full-field ... [more ▼]

We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning nearfield optical microscopy (SNOM). By means of full-field simulations it is demonstrated how the coupling of the hollow-pyramid aperture probe to the nanoantenna induces an effective magnetic dipole which efficiently excites surface plasmon resonances only at lateral magnetic field maxima. This excitation in turn affects the detected light intensity enabling the visualization of the lateral magnetic near-field distribution of multiple odd and even order plasmon modes with subwavelength spatial resolution. [less ▲]

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See detailLocal mapping of dissipative vortex motion
Raes, B; Van de Vondel, J; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2012), 86

We explore, with unprecedented single vortex resolution, the dissipation and motion of vortices in a superconducting ribbon under the influence of an external alternating magnetic field. This is achieved ... [more ▼]

We explore, with unprecedented single vortex resolution, the dissipation and motion of vortices in a superconducting ribbon under the influence of an external alternating magnetic field. This is achieved by combining the phase sensitive character of ac susceptibility, allowing us to distinguish between the inductive and dissipative responses, with the local power of scanning Hall probe microscopy. Whereas the induced reversible screening currents contribute only inductively, the vortices do leave a fingerprint in the out-of-phase component. The observed large phase-lag demonstrates the dissipation of vortices at time scales comparable to the period of the driving force (i.e., 13 ms). These results indicate the presence of slow microscopic loss mechanisms mediated by thermally activated hopping transport of vortices between metastable states. [less ▲]

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See detailControlling flux flow dissipation by changing flux pinning in superconducting films
Grimaldi, G; Leo, A; Nigro, A et al

in Applied Physics Letters (2012), 100

We study the flux flow state in superconducting materials characterized by rather strong intrinsic pinning, such as Nb, NbN, and nanostructured Al thin films, in which we drag the superconducting ... [more ▼]

We study the flux flow state in superconducting materials characterized by rather strong intrinsic pinning, such as Nb, NbN, and nanostructured Al thin films, in which we drag the superconducting dissipative state into the normal state by current biasing. We modify the vortex pinning strength either by ion irradiation, by tuning the measuring temperature or by including artificial pinning centers. We measure critical flux flow voltages for all materials and the same effect is observed: switching to low flux flow dissipations at low fields for an intermediate pinning regime. This mechanism offers a way to additionally promote the stability of the superconducting state. [less ▲]

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See detailInfluence of artificial pinning on vortex lattice instability in superconducting films
Silhanek, Alejandro ULg; Leo, A.; Grimaldi, G. et al

in New Journal of Physics (2012), 14

In superconducting films under an applied dc current, we analyze experimentally and theoretically the influence of engineered pinning on the vortex velocity at which the flux-flow dissipation undergoes an ... [more ▼]

In superconducting films under an applied dc current, we analyze experimentally and theoretically the influence of engineered pinning on the vortex velocity at which the flux-flow dissipation undergoes an abrupt transition from low to high resistance. We argue, based on a nonuniform distribution of vortex velocity in the sample, that in strongly disordered systems the mean critical vortex velocity for flux-flow instability (i) has a nonmonotonic dependence on magnetic field and (ii) decreases as the pinning strength is increased. These findings challenge the generally accepted microscopic model of Larkin and Ovchinnikov (1979 J. Low. Temp. Phys. 34 409) and all subsequent refinements of this model which ignore the presence of pinning centers. [less ▲]

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See detailLocalization of superconductivity in superconductor–electromagnet hybrids
Ataklti, G.W.; Aladyshkin, A.Yu.; Gillijns, W. et al

in Superconductor Science and Technology (2012), 25

We investigate the nucleation of superconductivity in a superconducting Al strip under the influence of the magnetic field generated by a current-carrying Nb wire, perpendicularly oriented and located ... [more ▼]

We investigate the nucleation of superconductivity in a superconducting Al strip under the influence of the magnetic field generated by a current-carrying Nb wire, perpendicularly oriented and located underneath the strip. The inhomogeneous magnetic field, induced by the Nb wire, produces a spatial modulation of the critical temperature Tc, leading to a controllable localization of the superconducting order parameter (OP) wavefunction. We demonstrate that close to the phase boundary Tc(Bext) the localized OP solution can be displaced reversibly by either applying an external perpendicular magnetic field Bext or by changing the amplitude of the inhomogeneous field. [less ▲]

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See detailChirality in nonlinear-optical response of planar G-shaped nanostructures
Mamonov, E.A.; Murzina, T.V.; Kolmychek, I.A. et al

in Optics Express (2012), 20(8), 8518

Chirality effects in optical second harmonic generation (SHG) are studied in periodic planar arrays of gold G-shaped nanostructures. We show that G-shaped structures of different handedness demonstrate ... [more ▼]

Chirality effects in optical second harmonic generation (SHG) are studied in periodic planar arrays of gold G-shaped nanostructures. We show that G-shaped structures of different handedness demonstrate different SHG efficiency for the left and right circular polarizations, as well as the opposite directions of the SHG polarization plane rotation. The observed effects are interpreted as the appearance of chirality in the SHG response which allows clear distinguishing of two enantiomers. [less ▲]

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See detailScanning Hall probe microscopy of unconventional vortex patterns in the two-gap MgB2 superconductor
Gutierrez, J.; Raes, B.; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2012), 85

The low magnetic field vortex patterns nucleation and evolution in a high-quality two-gap superconductor MgB2 single crystal have been investigated by low-temperature scanning Hall probe microscopy. Large ... [more ▼]

The low magnetic field vortex patterns nucleation and evolution in a high-quality two-gap superconductor MgB2 single crystal have been investigated by low-temperature scanning Hall probe microscopy. Large areas have been imaged with single-vortex resolution while changing systematically the thermodynamic parameters for field and temperature. The obtained patterns have been studied and compared with those of a reference 2H-NbSe2 single crystal. We found that the observed vortex patterns in MgB2 (e.g., stripes, clusters) appear due to competing vortex-vortex interactions as suggested by the theory of type-1.5 superconductivity. [less ▲]

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See detailVolumetric method of moments and conceptual multilevel building blocks for nanotopologies
Zheng, X.; Valev, V.K.; Verellen, N. et al

in IEEE Photonics Journal (2012), 4(1), 267-282

Based on the relationship between charge dimensionality and singular field behavior, it is proven that in a volumetric description of a volume current carrying topology, half rooftops of different binary ... [more ▼]

Based on the relationship between charge dimensionality and singular field behavior, it is proven that in a volumetric description of a volume current carrying topology, half rooftops of different binary hierarchical level are allowed without introducing numerical difficulties. This opens the possibility to use a very efficient multi-level hierarchical meshing scheme in a Volumetric Method of Moments (MoM) algorithm. The new meshing scheme is validated by numerical calculations and experiments. It paves the way towards a much more efficient use of MoM in the description of arbitrarily shaped nano-structures at IR and optical frequencies. [less ▲]

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See detailPlasmon-Enhanced Sub-Wavelength Laser Ablation: Plasmonic Nanojets
Valev, V.K.; Denkova, D.; Zheng, X. et al

in Advanced Materials (2012), 24

Plasmonic hotspots are regions on the surface of metal nanostructures where light causes very strong oscillation of the electrons. Because electron oscillations constitute an electric current and because ... [more ▼]

Plasmonic hotspots are regions on the surface of metal nanostructures where light causes very strong oscillation of the electrons. Because electron oscillations constitute an electric current and because electric currents heat up the material the same way an electric stove heats up in the kitchen, the plasmonic hotspots are extremely hot. So hot that they can melt the gold in a spot much smaller than the wavelength of light. We were successfully able to demonstrate that this tiny little pool of molten gold can give rise to the smallest nanojets ever observed. [less ▲]

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See detailFlux avalanches triggered by AC magnetic fields in superconducting thin films
Motta, M; Colauto, F; Johansen, TH et al

in Physica C (2012), 479

Flux avalanches are known to occur as a consequence of thermomagnetic instabilities. Some of their fingerprints are jumps in magnetization curves, or a paramagnetic reentrance in AC susceptibility ... [more ▼]

Flux avalanches are known to occur as a consequence of thermomagnetic instabilities. Some of their fingerprints are jumps in magnetization curves, or a paramagnetic reentrance in AC susceptibility measurements. In this work we have studied flux avalanches triggered by an AC field cycle by means of AC susceptibility and residual magnetization after an applied AC field measured as a function of an AC excitation field (h). These measurements allow comparing both results with magneto-optical imaging carried out in similar conditions. The results show a correspondence for the onset of the avalanche activity, as well as between the residual magnetic moment and the mean gray value calculated from the magneto-optical images in the remanent state. [less ▲]

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See detailCircular dichroism in optical second harmonic generated in reflection from chiral G-shaped metamaterials
Mamonov, Evgeniy; Kolmychek, Irina; Murzina, Tatiana et al

in Journal of Physics: Conference Series (2012), 352

Influence of chirality on the optical second harmonic generated from planar array of G-shaped metamaterials is studied. Circular dichroism of these nanostructures manifests itself via different efficiency ... [more ▼]

Influence of chirality on the optical second harmonic generated from planar array of G-shaped metamaterials is studied. Circular dichroism of these nanostructures manifests itself via different efficiency of left and right circularly polarized second harmonic that is observed for the samples of different handedness. This difference allows to distinguish between the two enantiomers. [less ▲]

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See detailSign reversal of the Hall resistance in the mixed-state of La1.89Ce0.11CuO4 and La1.89Ce0.11(Cu0.99Co0.01)O4 thin films
Jin, K; Wu, BX; Zhu, BY et al

in Physica C (2012), 479

The transport properties of La1.89Ce0.11CuO4(LCCO) and La1.89Ce0.11(Cu0.99Co0.01)O4 (LCCO:Co) superconducting thin films are investigated. When the external field H is applied along the crystallographic c ... [more ▼]

The transport properties of La1.89Ce0.11CuO4(LCCO) and La1.89Ce0.11(Cu0.99Co0.01)O4 (LCCO:Co) superconducting thin films are investigated. When the external field H is applied along the crystallographic c-axis, a double sign reversal of the Hall voltage in the mixed state of LCCO:Co thin films is observed whereas a single sign reversal is detected in LCCO. A double sign reversal of the Hall signal in LCCO can be recovered if the magnetic field is tilted away from the plane of the film. We find that the transition from one to two of the Hall sign reversal coincides with the change in the pinning from strong to weak. This temperature/field induced transition is caused either by the magnetic impurities in LCCO:Co or by the coupling between the pancake vortices and the in-plane Josephson vortices in LCCO. These results are in agreement with early theoretical and numerical predictions. [less ▲]

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See detailDistributing the Optical Near-Field for Efficient Field-Enhancements in Nanostructures
Valev, V; De Clercq, B; Biris, C et al

in Advanced Materials (2012), 24

Circularly polarized light imparts a sense of rotation on the electron density in ring-shaped gold nanostructures. As a consequence, the near-field enhancement becomes homogeneous on the surface of the ... [more ▼]

Circularly polarized light imparts a sense of rotation on the electron density in ring-shaped gold nanostructures. As a consequence, the near-field enhancement becomes homogeneous on the surface of the nanostructures, thereby increasing the opportunity for interaction with molecules. This type of nanostructured samples can find a broad range of applications in chemical processes where the interaction between molecules and local field enhancements play an important role. [less ▲]

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See detailRobustness of the scanning second harmonic generation microscopy technique for characterization of hotspot patterns in plasmonic nanomaterials
Valev, VK; De Clercq, B; Zheng, X et al

in Proceedings of SPIE (2012), 8424

Scanning second harmonic generation (SHG) microscopy is becoming an important tool for characterizing nanopatterned metal surfaces and mapping plasmonic local field enhancements. Here we study G-shaped ... [more ▼]

Scanning second harmonic generation (SHG) microscopy is becoming an important tool for characterizing nanopatterned metal surfaces and mapping plasmonic local field enhancements. Here we study G-shaped and mirror-G-shaped gold nanostructures and test the robustness of the experimental results versus the direction of scanning, the numerical aperture of the objective, the magnification, and the size of the laser spot on the sample. We find that none of these parameters has a significant influence on the experimental results. [less ▲]

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See detailSecond harmonic hotspots at the edges of the unit cells in G-shaped gold nanostructures
Valev, VK; Osley, EJ; De Clercq, B et al

in Proceedings of SPIE (2012), 8424

We report our latest results on second harmonic generation (SHG) microscopy from arrays of G-shaped chiral gold nanostructures. The nanostructures are arranged in unit cells composed of four Gs, each ... [more ▼]

We report our latest results on second harmonic generation (SHG) microscopy from arrays of G-shaped chiral gold nanostructures. The nanostructures are arranged in unit cells composed of four Gs, each rotated at 90° with respect to its neighbors. As it has already been demonstrated, for linearly polarized light, these unit cells yield a pattern of four SHG hotspots. However, upon increasing the pitch of the nanostructured arrays, extra hotspots can be observed at the edges of the unit cells. While the origin of these extra hotspots remains to be elucidated, their position indicates a relationship to coupling behavior between the unit cells. [less ▲]

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See detailImaging the statics and dynamics of vortex-antivortex molecules
Silhanek, Alejandro ULg

Conference (2011, September)

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See detailVortex deformation and stepper motors
Silhanek, Alejandro ULg

Conference (2011, August)

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