References of "Silhanek, Alejandro"
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See detailMesoscopic cross-film cryotrons: Vortex trapping and dc-Josephson-like oscillations of the critical current
Aladyshkin, A Yu; Ataklti, G. W.; Gillijns, W. et al

in Physical Review. B : Condensed Matter (2011), 83(14),

We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the ... [more ▼]

We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the superconducting strip. It is well known that the critical current of the superconducting strip, I(c), in such a cryotron-like system can be tuned by changing the current in the control wire, I(w). We demonstrated that the discrete change in the number of the pinned vortices/antivortices inside the narrow and long strip nearby the current-carrying wire results in a peculiar oscillatory dependence of I(c) on I(w). [less ▲]

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See detailVisualizing the ac magnetic susceptibility of superconducting films via magneto-optical imaging
Motta, M.; Colauto, F.; Zadorosny, R. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 84(21), 214529

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical ... [more ▼]

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical measurements. The investigated samples are three Nb films: a plain specimen, used as a reference sample, and other two films patterned with square arrays of antidots. At low temperatures and small ac amplitudes of the excitation field, the Meissner screening prevents penetration of flux into the sample. Above a certain ac drive threshold, flux avalanches are triggered during the first cycle of the ac excitation. The subsequent periodic removal, inversion, and rise of flux occurs essentially through the already-created dendrites, giving rise to an ac susceptibility signal weakly dependent on the applied field. The intradendrite flux oscillation is followed, at higher values of the excitation field, by a more drastic process consisting of creation of new dendrites and antidendrites. In this more invasive regime, the ac susceptibility shows a clear field dependence. At higher temperatures a smooth penetration occurs, and the flux profile is characteristic of a critical state. We have also shown that the regime dominated by vortex avalanches can be reliably identified by ac susceptibility measurements. [less ▲]

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See detailThe role of chiral local field enhancements below the resolution limit of Second Harmonic Generation microscopy
Valev, V.; Clercq, B.; Zheng, X. et al

in Optics Express (2011), 20(1), 256

While it has been demonstrated that, above its resolution limit, Second Harmonic Generation (SHG) microscopy can map chiral local field enhancements, below that limit, structural defects were found to ... [more ▼]

While it has been demonstrated that, above its resolution limit, Second Harmonic Generation (SHG) microscopy can map chiral local field enhancements, below that limit, structural defects were found to play a major role. Here we show that, even below the resolution limit, the contributions from chiral local field enhancements to the SHG signal can dominate over those by structural defects. We report highly homogeneous SHG micrographs of star-shaped gold nanostructures, where the SHG circular dichroism effect is clearly visible from virtually every single nanostructure. Most likely, size and geometry determine the dominant contributions to the SHG signal in nanostructured systems. [less ▲]

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See detailPlasmons Reveal the Direction of Magnetization in Nickel Nanostructures
Valev, Ventsislav K; Silhanek, Alejandro ULg; Gillijns, Werner et al

in ACS Nano (2011), 5(1), 91-96

We have applied the surface sensitive nonlinear optical technique of magnetization induced second harmonic generation. (MSHG) to plasmonic, magnetic nanostructures made of Ni. We show that surface plasmon ... [more ▼]

We have applied the surface sensitive nonlinear optical technique of magnetization induced second harmonic generation. (MSHG) to plasmonic, magnetic nanostructures made of Ni. We show that surface plasmon contributions to the MSHG signal can reveal the direction of the magnetization. Both the plasmonic and the magnetic nonlinear optical responses can be tuned; our results indicate novel ways to combine nanophotonics, nanoelectronics, and nanomagnetics and suggest the possibility for large magneto-chiral effects in metamaterials. [less ▲]

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See detailHotspot Decorations Map Plasmonic Patterns with the Resolution of Scanning Probe Techniques
Valev, V. K.; Silhanek, Alejandro ULg; Jeyaram, Y. et al

in Physical Review Letters (2011), 106(22),

In high definition mapping of the plasmonic patterns on the surfaces of nanostructures, the diffraction limit of light remains an important obstacle. Here we demonstrate that this diffraction limit can be ... [more ▼]

In high definition mapping of the plasmonic patterns on the surfaces of nanostructures, the diffraction limit of light remains an important obstacle. Here we demonstrate that this diffraction limit can be completely circumvented. We show that upon illuminating nanostructures made of nickel and palladium, the resulting surface-plasmon pattern is imprinted on the structures themselves; the hotspots (regions of local field enhancement) are decorated with overgrowths, allowing for their subsequent imaging with scanning-probe techniques. The resulting resolution of plasmon pattern imaging is correspondingly improved. [less ▲]

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See detailCoherent and incoherent second harmonic generation in planar G-shaped nanostructures
Mamonov, E. A.; Murzina, T. V.; Kolmychek, I. A. et al

in Optics Letters (2011), 36(18), 3681-3683

Azimuthal anisotropy of Stokes parameters of the second harmonic generation ( SHG) generated and observed in reflection from a periodic planar area of G-shaped gold nanostructures is studied. A strong ... [more ▼]

Azimuthal anisotropy of Stokes parameters of the second harmonic generation ( SHG) generated and observed in reflection from a periodic planar area of G-shaped gold nanostructures is studied. A strong anisotropy of both coherent and incoherent SHG components is observed. Finite-difference time-domain calculations prove that the observed effects are due to the anisotropic enhancement of the fundamental radiation within the G-shaped structures. (C) 2011 Optical Society of America [less ▲]

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See detailLocal probing of the vortex-antivortex dynamics in superconductor/ferromagnet hybrid structures
Silhanek, Alejandro ULg; Gladilin, V. N.; Van de Vondel, J. et al

in Superconductor Science and Technology (2011), 24(2),

In-plane ferromagnetic bars, densely packed in a linear array underneath a superconducting bridge, create two types of vortex chains of opposite polarity inside the superconductor. In this work we ... [more ▼]

In-plane ferromagnetic bars, densely packed in a linear array underneath a superconducting bridge, create two types of vortex chains of opposite polarity inside the superconductor. In this work we investigate both experimentally and theoretically the dynamics of these vortex chains as a function of an external magnetic field for two different arrangements of magnetic moments, namely parallel and antiparallel. The theoretical approach, based on the time-dependent Ginzburg-Landau formalism, confirms previously proposed empirical models implemented to describe the basic properties of these hybrid systems. In addition, local transport measurements allow us to probe the dynamics of individual vortex channels as a function of the applied magnetic field. These measurements evidence a drastic reduction of the dissipation in the channel populated with vortices having opposite polarity to the applied field. [less ▲]

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See detailU-Shaped Switches for Optical Information Processing at the Nanoscale
Valev, Ventsislav K; Silhanek, Alejandro ULg; De Clercq, Ben et al

in Small : Nano Micro (2011), 7(18), 2573-2576

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See detailLinearly polarized second harmonic generation microscopy reveals chirality (vol 18, pg 8286, 2010)
Valev, V. K.; Silhanek, Alejandro ULg; Smisdom, N. et al

in Optics Express (2011), 19(10), 9242-9244

An erratum is presented to clarify both the direction of light polarization in our experiments and the unit cell geometry of the samples. Additionally, the spectral dependence of the second harmonic ... [more ▼]

An erratum is presented to clarify both the direction of light polarization in our experiments and the unit cell geometry of the samples. Additionally, the spectral dependence of the second harmonic generation response in the G-shaped nanostructures made of gold is corrected. These changes do not affect our previous conclusions. (C) 2011 Optical Society of America [less ▲]

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See detailMicroscopic picture of the critical state in a superconductor with a periodic array of antidots
Silhanek, Alejandro ULg; Gutierrez, J.; Kramer, R. B. G. et al

in Physical Review. B : Condensed Matter (2011), 83(2),

By using scanning Hall microscopy we visualize the progressive formation of the critical state with individual vortex resolution in a Pb thin film with a periodic pinning array. Slightly above the first ... [more ▼]

By using scanning Hall microscopy we visualize the progressive formation of the critical state with individual vortex resolution in a Pb thin film with a periodic pinning array. Slightly above the first penetration field, we directly observe a terraced critical state as proposed theoretically by Cooley and Grishin [Phys. Rev. Lett. 74, 2788 (1995)]. However, at higher fields, the flux front tends to disorder and the classical Bean profile is restored. This study allows us to establish a clear link between the widely used integrated response measurements in the superconducting state and the nanoscale landscape defined by individual vortices. [less ▲]

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See detailElectrical and Magnetic Characterization of BSCCO and YBCO HTS Tapes for Fault Current Limiter Application
Lamas, Jerika S; Baldan, Carlos A; Shigue, Carlos Y et al

in IEEE Transactions on Applied Superconductivity (2011), 21(3), 3398-3402

Several high temperature superconductor (HTS) tapes have been developed since the late eighties. Due to the new techniques applied for their production, HTS tapes are becoming feasible and practical for ... [more ▼]

Several high temperature superconductor (HTS) tapes have been developed since the late eighties. Due to the new techniques applied for their production, HTS tapes are becoming feasible and practical for many applications. In this work, we present the test results of five commercial HTS tapes from the BSCCO and YBCO families (short samples of 200 mm). We have measured and analyzed their intrinsic and extrinsic properties and compared their behaviors for fault current limiter (FCL) applications. Electrical measurements were performed to determine the critical current and the n value through the V-I relationship under DC and AC magnetic fields. The resistance per unit length was determined as a function of temperature. The magnetic characteristics were analyzed through susceptibility curves as a function of temperature. As transport current generates a magnetic field surrounding the HTS material, the magnetic measurements indicate the magnetic field supported by the tapes under a peak current 1.5 times higher than the critical current, I(c). By pulsed current tests the recovery time and the energy/volume during a current fault were also analyzed. These results are in agreement with the data found in the literature giving the most appropriate performance conductor for a FCL device (I(peak) = 4 kA) to be used in a 220 V-60 Hz grid. [less ▲]

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See detailVortex Dynamics in a Superconducting Film with a Kagome and a Honeycomb Pinning Landscape
Cuppens, J.; Ataklti, G. W.; Gillijns, W. et al

in Journal of Superconductivity & Novel Magnetism (2011), 24(1-2), 7-11

The vortex dynamics in a superconducting thin Al film with a periodic Honeycomb or Kagome array of antidots has been investigated by electrical transport measurements. The large values of the ... [more ▼]

The vortex dynamics in a superconducting thin Al film with a periodic Honeycomb or Kagome array of antidots has been investigated by electrical transport measurements. The large values of the superconducting coherence length and penetration depth of the Al films guarantee a maximum of one flux quantum trapped per pinning site. This allows us to directly compare the experimental results with previous theoretical investigations based on molecular dynamics simulations. For the Kagome lattice, two submatching features not anticipated theoretically at H/H (1)=1/3 and 2/3, where H (1) is the field at which the number of vortices coincides with the number of pinning sites, are observed. Possible corresponding stable vortex patterns are suggested. For the Honeycomb pinning landscape, the commensurability effects are in agreement with the theoretical expectations. A preliminary analysis of the vortex mobility in this lattice shows the presence of a weak vortex guidance. [less ▲]

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See detailBacteria and nanoscale biophysics
Silhanek, Alejandro ULg; Vanderleyden, Jozef

in Microbial Biotechnology (2011), 4(2), 129-130

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See detailVortex Core Deformation and Stepper-Motor Ratchet Behavior in a Superconducting Aluminum Film Containing an Array of Holes
Van de Vondel, J.; Gladilin, V. N.; Silhanek, Alejandro ULg et al

in Physical Review Letters (2011), 106(13),

We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time-dependent ... [more ▼]

We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time-dependent Ginzburg-Landau formalism. We demonstrate that the high frequency vortex behavior can be described as a discrete motion of a particle in a periodic potential, i.e., the so-called stepper-motor behavior. Strikingly, in the more conventional low frequency response a transition takes place from an Abrikosov vortex rectifier to a phase slip line rectifier. This transition is characterized by a strong increase in the rectified voltage and the appearance of a pronounced hysteretic behavior. [less ▲]

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See detailField polarity dependent nucleation of superconductivity in quasi-one-dimensional magnetic templates
Ataklti, G. W.; Silhanek, Alejandro ULg; Van de Vondel, J. et al

in Physica C: Superconductivity (2010), 470(19), 860-862

We investigate the nucleation of superconductivity in an Al/Al(2)O(3)/Py trilayer system by electrical transport measurements. Magnetic force microscopy images taken at room temperature show that the 0.7 ... [more ▼]

We investigate the nucleation of superconductivity in an Al/Al(2)O(3)/Py trilayer system by electrical transport measurements. Magnetic force microscopy images taken at room temperature show that the 0.7 mu m thick Py-film form stripes of magnetic domains with alternating out-of-plane stray field. After applying a strong out of plane magnetic field H the superconductor/normal phase boundary becomes asymmetric with respect to H = 0. This lack of field polarity symmetry results from the unbalanced size distribution of domains with opposite polarity. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailFormation of Stripelike Flux Patterns Obtained by Freezing Kinematic Vortices in a Superconducting Pb Film
Silhanek, Alejandro ULg; Milosevic, M. V.; Kramer, R. B. G. et al

in Physical Review Letters (2010), 104(1),

We demonstrate experimentally and theoretically that the dissipative state of superconducting samples with a periodic array of holes at high current densities consists of flux rivers resulting from a ... [more ▼]

We demonstrate experimentally and theoretically that the dissipative state of superconducting samples with a periodic array of holes at high current densities consists of flux rivers resulting from a short-range attractive interaction between vortices. This dynamically induced vortex-vortex attraction results from the migration of quasiparticles out of the vortex core (kinematic vortices). We have directly visualized the formation of vortex chains by scanning Hall probe microscopy after freezing the dynamic state by a field cooling procedure at a constant bias current. Similar experiments carried out in a sample without holes show no hint of flux river formation. We shed light on this nonequilibrium phenomena modeled by time-dependent Ginzburg-Landau simulations. [less ▲]

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See detailAsymmetric Optical Second-Harmonic Generation from Chiral G-Shaped Gold Nanostructures
Valev, V. K.; Silhanek, Alejandro ULg; Verellen, N. et al

in Physical Review Letters (2010), 104(12),

We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating ... [more ▼]

We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating the sample in an experiment involving solely linearly polarized light. This phenomenon originates in the surface plasmon resonance of chiral gold nanostructures, where homodyne interference of anisotropic and chiral electric and/or magnetic multipoles appears to play an important role. [less ▲]

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See detailDirect visualization of the Campbell regime in superconducting stripes
Kramer, R. B. G.; Ataklti, G. W.; Moshchalkov, V. V. et al

in Physical Review. B : Condensed Matter (2010), 81(14),

A combination of scanning Hall microscopy and scanning ac-susceptibility measurements in superconducting stripes (ribbons) of width w < 10 mu m was used to observe the dimensional phase transitions of the ... [more ▼]

A combination of scanning Hall microscopy and scanning ac-susceptibility measurements in superconducting stripes (ribbons) of width w < 10 mu m was used to observe the dimensional phase transitions of the vortex lattice and its stability under alternating fields. At low dc magnetic fields applied perpendicularly to the plane of the stripes, vortices form a one-dimensional chain at the center of the stripes. Above a certain field H*(w), the vortex chain splits in two parallel rows displaced laterally in such a way that a zigzag vortex pattern is observed. By shaking the vortices with an external magnetic ac field and detecting their in-phase motion locally, we can identify the degree of mobility of each individual vortex. This technique allows us (i) to directly visualize the transition from intravalley (Campbell regime) to intervalley vortex motion as the amplitude of the ac modulation is increased and (ii) to accurately determine the temperature at which the vortex lattice freezes in a field-cooling experiment. [less ▲]

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See detailGuided vortex motion and vortex ratchets in nanostructured superconductors
Silhanek, Alejandro ULg; Van de Vondel, J.; Moshchalkov, V.V.

in Moshchalkov, V.V.; Woerdenweber, R.; Lang, W. (Eds.) Nanoscience and Engineering in Superconductivity (2010)

In type II superconductors, an external magnetic field can partially penetrate into the superconducting phase in the form of magnetic flux lines or vortices. The repulsive interaction between vortices ... [more ▼]

In type II superconductors, an external magnetic field can partially penetrate into the superconducting phase in the form of magnetic flux lines or vortices. The repulsive interaction between vortices makes them to arrange in a triangular lattice, known as Abrikosov vortex lattice. This periodic vortex distribution is very fragile and can be easily distorted by introducing pinning centers such as local alterations of the superconducting condensate density. The dominant role of the vortex-pinning site interaction not only permits to control the static vortex patterns and to enhance the maximum dissipationless current sustainable by the superconducting material but also allows one to gain control on the dynamics of vortices. Among the ultimate motivations behind the manipulation of the vortex motion are the better performance of superconductor-based devices by reducing the noise in superconducting quantum interference-based systems, development of superconducting terahertz emitters, reversiblemanipulation of local field distribution through flux lenses, or even providing a way to predefine the optical transmission through the system. In this chapter, we discuss two relevant mechanisms used in most envisaged fluxonics devices, namely the guidance of vortices through predefined paths and the rectification of the average vortex motion. The former can be achieved with any sort of confinement potential such as local depletion of the order parameter or local enhancements of the current density. In contrast, rectification effects result from the lack of inversion symmetry of the pinning landscape which tends to favor the vortex flow in one particular direction. We also discuss a new route for further flexibility and tunability of these fluxonics components by introducing ferromagnetic pinning centers interacting with vortices via their magnetic stray field. [less ▲]

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See detailFreezing vortex rivers
Silhanek, Alejandro ULg; Kramer, R. G. B.; Van de Vondel, J. et al

in Physica C: Superconductivity (2010), 470(19), 726-729

We demonstrate experimentally and theoretically that the dissipative state at high current densities of superconducting samples with a periodic array of holes consist of flux rivers resulting from a short ... [more ▼]

We demonstrate experimentally and theoretically that the dissipative state at high current densities of superconducting samples with a periodic array of holes consist of flux rivers resulting from a short range attractive interaction between vortices. This dynamically induced vortex-vortex attraction results from the migration of quasiparticles out of the vortex core. We have directly visualized the formation of vortex chains by scanning Hall microscopy after freezing the dynamic state by a field cooling procedure at constant bias current. Similar experiments carried out in a sample without holes show no hint of flux river formation. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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