References of "Gillijns, W"
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See detailEnhanced pinning in superconducting thin films with graded pinning landscapes
Motta, M.; Colauto, F.; Ortiz, W.A. et al

in Applied Physics Letters (2013), 102

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 ... [more ▼]

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 [Phys. Rev. B 85, 184506 (2012)]. [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 detailImaging the Statics and Dynamics of Superconducting Vortices and Antivortices Induced by Magnetic Microdisks
Kramer, R. B. G.; Silhanek, Alejandro ULg; Gillijns, W. et al

in Physical Review X (2011), 1(2), 021004

If a magnet of microscopic dimensions is brought in close proximity to a superconductor, the quantized nature of their interaction due to the creation of flux quanta in the superconducting system becomes ... [more ▼]

If a magnet of microscopic dimensions is brought in close proximity to a superconductor, the quantized nature of their interaction due to the creation of flux quanta in the superconducting system becomes noticeable. Herein, we directly image, via scanning Hall microscopy, the vortex-antivortex pairs in a superconducting film created by micromagnets. The number of antivortices at equilibrium conditions can be changed either by tuning the magnetic moment of the magnets or by annihilation with externally induced vortices. We demonstrate that small ac field excitations shake the antivortices sitting next to the micromagnets whereas no sizable motion is observed for the vortices sitting on top of the magnets, clearly revealing the different mobility of these two vortex species. A metastable state, which is obtained by applying a field after the system has been cooled down below the superconducting transition, shows a complex graded distribution of coexisting vortices and antivortices forming an intertwined critical state. [less ▲]

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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 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 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 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 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 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 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 detailField polarity dependent superconducting properties in a superconductor/ferromagnet hybrid with in-plane magnetic moment
Gillijns, W.; Godts, F.; Ataklti, G. W. et al

in Physica C: Superconductivity (2010), 470(19), 880-882

The transport properties of an Al type-II superconducting thin film covering a Py plain film with a rectangular array of triangular holes are investigated. We show that, although the magnetization of the ... [more ▼]

The transport properties of an Al type-II superconducting thin film covering a Py plain film with a rectangular array of triangular holes are investigated. We show that, although the magnetization of the Py lies in the plane of the structure, both the critical temperature and the critical current are asymmetric with respect to the polarity of the external field, which is applied perpendicularly to the structure. The asymmetric nucleation can be explained in terms of field compensation effects between internal and external magnetic fields, whereas the presence of vortex-antivortex pairs are responsible for the observed features in the critical current. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailPinning effects on the vortex critical velocity in type-II superconducting thin films
Leo, A.; Grimaldi, G.; Nigro, A. et al

in Physica C: Superconductivity (2010), 470(19), 904-906

We study the influence of artificial pinning centers on the vortex critical velocity in Al thin films deposited on top of a periodic array of Permalloy (FeNi) square rings. We demonstrate that the field ... [more ▼]

We study the influence of artificial pinning centers on the vortex critical velocity in Al thin films deposited on top of a periodic array of Permalloy (FeNi) square rings. We demonstrate that the field dependence of the flux flow velocity strongly depends on the particular magnetic state of the rings. In particular, we find that, even when the rings are in a flux closure state, i.e. with little stray field, the vortex critical velocity shows a non-monotonic magnetic field dependence. This behaviour is in sharp contrast with the results obtained in a reference plain film, with no rings underneath. A comparison with the intrinsic strong pinning Nb films previously studied, suggests an interpretation in terms of a channel-like motion of vortices, here induced by the artificial pinning structure. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailLinearly polarized second harmonic generation microscopy reveals chirality
Valev, V. K.; Silhanek, Alejandro ULg; Smisdom, N. et al

in Optics Express (2010), 18(8), 8286-8293

In optics, chirality is typically associated with circularly polarized light. Here we present a novel way to detect the handedness of chiral materials with linearly polarized light. We performed Second ... [more ▼]

In optics, chirality is typically associated with circularly polarized light. Here we present a novel way to detect the handedness of chiral materials with linearly polarized light. We performed Second Harmonic Generation (SHG) microscopy on G-shaped planar chiral nanostructures made of gold. The SHG response originates in distinctive hotspots, whose arrangement is dependent of the handedness. These results uncover new directions for studying chirality in artificial materials. (C) 2010 Optical Society of America [less ▲]

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See detailGuided nucleation of superconductivity on a graded magnetic substrate
Milosevic, M. V.; Gillijns, W.; Silhanek, Alejandro ULg et al

in Applied Physics Letters (2010), 96(3),

We demonstrate the controlled spatial nucleation of superconductivity in a thin film deposited on periodic arrays of ferromagnetic dots with gradually increasing diameter. The perpendicular magnetization ... [more ▼]

We demonstrate the controlled spatial nucleation of superconductivity in a thin film deposited on periodic arrays of ferromagnetic dots with gradually increasing diameter. The perpendicular magnetization of the dots induces vortex-antivortex molecules in the sample, with the number of (anti)vortices increasing with magnet size. The resulting gradient of antivortex density between the dots predetermines local nucleation of superconductivity in the sample as a function of the applied external field and temperature. In addition, the compensation between the applied magnetic field and the antivortices results in an unprecedented enhancement of the critical temperature. [less ▲]

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See detailTransition from turbulent to nearly laminar vortex flow in superconductors with periodic pinning
Gutierrez, J.; Silhanek, Alejandro ULg; Van de Vondel, J. et al

in Physical Review. B : Condensed Matter (2009), 80(14),

We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex ... [more ▼]

We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex flow transition which manifests itself as a negative differential resistivity. This transition is accompanied by a strong irreversibility in the voltage-current characteristics. The dynamical phase diagrams obtained as a function of commensurability, temperature, and driving force are in good agreement with the early predictions by Reichhardt et al. [Phys. Rev. Lett. 78, 2648 (1997)] based on molecular dynamic simulations. [less ▲]

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See detailA Study of Chirality in Gold Nanostructures with Second Harmonic Generation
Valev, V. K.; Silhanek, Alejandro ULg; Gillijns, W. et al

in Acta Physica Polonica A (2009), 116(4), 498-500

We present the second harmonic generation - circular dichroism response from C-shaped gold nanostructures for P-polarized incoming light. By eliminating the contributions of anisotropy to the signal, an ... [more ▼]

We present the second harmonic generation - circular dichroism response from C-shaped gold nanostructures for P-polarized incoming light. By eliminating the contributions of anisotropy to the signal, an absolute measure of the second harmonic generation - circular dichroism is presented. The system of planar nanostructures is an excellent model for studying the correlation between optical properties and chiral morphology at the nanoscale. Samples with both enantiomorphs of the chiral pattern were prepared and, demonstrating the unambiguous presence of chirality, the second harmonic generation - circular dichroism response from two such samples was fitted simultaneously with a single set of fitting parameters. [less ▲]

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See detailPlasmonic Ratchet Wheels: Switching Circular Dichroism by Arranging Chiral Nanostructures
Valev, V. K.; Smisdom, N.; Silhanek, Alejandro ULg et al

in Nano Letters (2009), 9(11), 3945-3948

We demonstrate circular dichroism (CD) in the second harmonic generation (SHG) signal from chiral assemblies of G-shaped nanostructures made of gold. The arrangement of the G shapes is crucial since upon ... [more ▼]

We demonstrate circular dichroism (CD) in the second harmonic generation (SHG) signal from chiral assemblies of G-shaped nanostructures made of gold. The arrangement of the G shapes is crucial since upon reordering them the SHG-CD effect disappears. Microscopy reveals SHG "hotspots" assemblies, which originate in enantiomerically sensitive plasmon modes, having the novel property of exhibiting a chiral geometry themselves in relation with the handedness of the material. These results open new frontiers in studying chirality. [less ▲]

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See detailMagnetically controlled superconducting weak links
Van de Vondel, J.; Silhanek, Alejandro ULg; Raes, B. et al

in Applied Physics Letters (2009), 95(3),

We have designed and characterized a magnetic template which can be switched between chains of parallel and antiparallel field distribution by applying an in-plane magnetic field. The parallel field ... [more ▼]

We have designed and characterized a magnetic template which can be switched between chains of parallel and antiparallel field distribution by applying an in-plane magnetic field. The parallel field profile creates highly mobile vortex channels in a superconducting film deposited on top, reproducing the behavior of a weak link as evidenced by the presence of Shapiro steps in the current-voltage characteristics under rf excitation. The Josephson coupling can be fully suppressed by changing the field distribution to the antiparallel state. As a result, a reversible ON/OFF switch for magnetically induced weak links has been demonstrated. [less ▲]

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