References of "Raedts, S"
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See detailEnhanced vortex trapping by a composite antidot lattice in a superconducting Pb film
Silhanek, Alejandro ULg; Van Look, L.; Jonckheere, R. et al

in Physica C: Superconductivity (2007), 460

Using electrical transport measurements, we study a composite antidot lattice consisting of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. We show ... [more ▼]

Using electrical transport measurements, we study a composite antidot lattice consisting of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. We show that placing an additional small antidot in the unit cell of the array a higher number of flux quanta per unit cell can be trapped inside the antidots, compared to a reference antidot film without the additional small antidots. As a consequence, the field range in which an enhanced critical current is observed is considerably expanded. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailCrossover from intravalley to intervalley vortex motion in type-II superconductors with a periodic pinning array
Raedts, S.; Silhanek, Alejandro ULg; Moshchalkov, V. V. et al

in Physical Review. B : Condensed Matter (2006), 73(17),

We have determined the transition from intravalley vortex motion (Campbell regime) to intervalley motion (critical state regime) in Pb thin films with and without a square array of holes (antidots) by ... [more ▼]

We have determined the transition from intravalley vortex motion (Campbell regime) to intervalley motion (critical state regime) in Pb thin films with and without a square array of holes (antidots) by means of ac susceptibility chi(T,H) measurements. The Campbell regime is characterized by a maximum dissipation chi(')(max) dependent on the ac excitation h but nearly temperature independent. In contrast, in the critical state regime, the height of the dissipation peak remains constant, whereas its position shifts to lower temperatures with increasing h. We introduce an alternative way for determining the temperature dependence of the ac onset of the Bean critical state by analyzing the critical current density J(T) extracted from the chi(')(T) data at several h. We demonstrate that the presence of a periodic pinning array strongly affects the extension of the crossover area in the h-T diagram between these regimes. We show that this effect can be ascribed to the lower dispersion of the pinning energy together with the higher topological order for the antidot sample. [less ▲]

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See detailAnisotropic avalanches and flux penetration in patterned superconductors
Gheorghe, D. G.; Menghini, M.; Wijngaarden, R. J. et al

in Physica C: Superconductivity (2006), 437-38

Both for a fundamental understanding of the flux penetration process and for technical applications, the role of artificial pinning sites (such as antidots) in superconductors generates a lot of interest ... [more ▼]

Both for a fundamental understanding of the flux penetration process and for technical applications, the role of artificial pinning sites (such as antidots) in superconductors generates a lot of interest. We perform magneto-optical imaging experiments on type-II Pb thin films patterned with square arrays of square antidots and square arrays of rectangular antidots and blind holes. We demonstrate that a square lattice of rectangular antidots can lead to similar anisotropy in flux penetration and critical current as a rectangular lattice of square antidots. In addition we show how thermo-magnetic avalanches can be guided-and hence to a certain extend controlled-by such holes. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailEnhanced vortex pinning by a composite antidot lattice in a superconducting Pb film
Silhanek, Alejandro ULg; Van Look, L.; Jonckheere, R. et al

in Physical Review. B : Condensed Matter (2005), 72(1),

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes (antidots ... [more ▼]

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes (antidots) substantially increase the critical temperature T-c(H) and critical current I-c(H) for all fields. Using electrical transport measurements, we study the effect of placing an additional small antidot in the unit cell of the array. This composite antidot lattice consists of two interpenetrating antidot square arrays with a different antidot size and the same lattice period. The smaller antidots are located at the centers of the cells of the large antidots array. We show that the composite antidot lattice can trap a higher number of flux quanta per unit cell inside the antidots compared to a reference antidot film without the additional small antidots. As a consequence, the field range in which an enhanced critical current is observed is considerably expanded. Finally, the possible stable vortex lattice patterns at several matching fields are determined by molecular-dynamics simulations. [less ▲]

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See detailDendritic flux penetration in Pb films with a periodic array of antidots
Menghini, M.; Wijngaarden, R. J.; Silhanek, Alejandro ULg et al

in Physical Review. B : Condensed Matter (2005), 71(10),

We explore the flux-jump regime in type-II Pb thin films with a periodic array of antidots by means of magneto-optical measurements. A direct visualization of the magnetic flux distribution allows us to ... [more ▼]

We explore the flux-jump regime in type-II Pb thin films with a periodic array of antidots by means of magneto-optical measurements. A direct visualization of the magnetic flux distribution allows us to identify a rich morphology of flux penetration patterns. We determine the phase boundary H-*(T) between dendritic penetration at low temperatures and a smooth flux invasion at high temperatures and fields. For the whole range of fields and temperatures studied, guided vortex motion along the principal axes of the square pinning array is clearly observed. In particular, the branching process of the dendrite expansion is fully governed by the underlying pinning topology. A comparative study between macroscopic techniques and direct local visualization sheds light onto the puzzling T- and H-independent magnetic response observed at low temperatures and fields. Finally, we find that the distribution of avalanche sizes at low temperatures can be described by a power law with exponent tau similar to 0.9(1). [less ▲]

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See detailFlux-pinning properties of superconducting films with arrays of blind holes
Raedts, S.; Silhanek, Alejandro ULg; Van Bael, M. J. et al

in Physical Review. B : Condensed Matter (2004), 70(2),

We performed ac susceptibility measurements to explore the vortex dynamics and the flux-pinning properties of superconducting Pb films with an array of microholes (antidots) and not fully perforated holes ... [more ▼]

We performed ac susceptibility measurements to explore the vortex dynamics and the flux-pinning properties of superconducting Pb films with an array of microholes (antidots) and not fully perforated holes (blind holes). A lower ac shielding together with a smaller extension of the linear regime for the lattice of blind holes indicates that these centers provide a weaker pinning potential than antidots. Moreover, we found that the maximum number of flux quanta trapped by a pinning site, i.e., the saturation number n(s), is lower for the blind hole array. [less ▲]

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See detailExperimental determination of the number of flux lines trapped by microholes in superconducting samples
Silhanek, Alejandro ULg; Raedts, S.; Van Bael, M. J. et al

in Physical Review. B : Condensed Matter (2004), 70(5),

The influence of a periodic landscape of pinning sites on the vortex dynamics in Pb thin films is explored by ac susceptibility measurements. For different amplitudes h of the ac drive, the ac ... [more ▼]

The influence of a periodic landscape of pinning sites on the vortex dynamics in Pb thin films is explored by ac susceptibility measurements. For different amplitudes h of the ac drive, the ac susceptibility chi=chi'+ichi" exhibits a complex field dependence associated with different dynamic regimes. At very low ac drives where both multiquanta vortices trapped by the antidots and interstitial vortices oscillate inside the pinning potential (intravalley motion), a small kink in chi'(H) together with a very low dissipation is observed. At intermediate ac excitations such that vortices in the antidots remain pinned, whereas interstices are driven out of the pinning well, a more pronounced kink in the screening coinciding with the onset of dissipation [chi"(H)not equal0] indicates the entrance of interstitial vortices. Eventually, at high enough amplitudes all vortices are set in motion and the penetration of interstitial vortices appears as a sudden reduction of the shielding power. We show that these distinctive features allow us to identify clearly the maximum number of flux quanta per hole, regardless of the vortex dynamic regime. [less ▲]

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See detailParamagnetic reentrance of ac screening: Evidence of vortex avalanches in Pb thin films
Silhanek, Alejandro ULg; Raedts, S.; Moshchalkov, V. V.

in Physical Review. B : Condensed Matter (2004), 70(14),

We have studied the influence of a square array of pinning centers on the dynamics of vortex avalanches in Pb thin films by means of ac- and dc-magnetization measurements. Close to the superconducting ... [more ▼]

We have studied the influence of a square array of pinning centers on the dynamics of vortex avalanches in Pb thin films by means of ac- and dc-magnetization measurements. Close to the superconducting transition T-c, the commensurability between the vortex lattice and the pinning array leads to the well known local increments of the critical current. As temperature T decreases, matching features progressively fade out and eventually disappear. Further down in temperature, vortex avalanches develop and dominate the magnetic response. These avalanches manifest themselves as jumps in the dc magnetization and produce a lower ac shielding, giving rise to a paramagnetic reentrance in the ac screening chi(')(T). Within the flux-jump regime, two subregimes can be identified. Close to the boundary where vortex avalanches develop, the field separation between consecutive jumps follows the periodicity of the pinning array and a field- and temperature-dependent screening is observed. In this regime, the response also depends on frequency f in agreement with theoretical models for magnetothermal instabilities. At low enough temperatures and fields, the screening saturates to a constant value independent of T, H, and f, where jumps are randomly distributed. We have also found that vortex instabilities occupy a larger portion of the H-T diagram in patterned samples than in films without nanoengineered pinning sites. Finally, we discuss the possible origin of the vortex avalanches and compare our results with previous experimental and theoretical studies. [less ▲]

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See detailAc response of Pb thin films with a periodic pinning potential
Silhanek, Alejandro ULg; Raedts, S.; Moshchalkov, V. V.

in Physica C: Superconductivity (2004), 404(1-4), 345-349

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T, H) measurements. For low amplitudes h of the ac excitation, the field dependence ... [more ▼]

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T, H) measurements. For low amplitudes h of the ac excitation, the field dependence of the ac susceptibility exhibits a series of distinctive features associated with the presence of different dynamic regimes. For fields below a certain characteristic field H-s, vortices strongly pinned by the antidots perform an oscillatory movement inside the pinning potential induced by the external ac drive. For fields between H-s and H-p, interstitial vortices, performing an intra-valley motion in the weak potential wells produced by the repulsive interaction of their pinned neighbors, dominate the ac response. For H-p < H < H-t, the interstitial vortices are driven out of their pinning sites while vortices in the antidots remain trapped. For higher fields all vortices are set in motion and a critical state develops. We show that the characteristic h-independent field H-s allows one to clearly identify the maximum number of flux quanta per hole. Unlike H-s, the fields H-p and H-t, signaling the onset of motion of interstitial vortices and vortices trapped by the antidots, respectively, strongly depend on h. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailFlux pinning properties of holes and blind holes arranged periodically in a superconductor
Raedts, S.; Silhanek, Alejandro ULg; Van Bael, M. J. et al

in Physica C: Superconductivity (2004), 404(1-4), 298-301

We investigate the dynamic response of a vortex lattice in nanostructured superconducting Pb films by means of ac-magnetization measurements. We compare the flux pinning properties of superconducting Pb ... [more ▼]

We investigate the dynamic response of a vortex lattice in nanostructured superconducting Pb films by means of ac-magnetization measurements. We compare the flux pinning properties of superconducting Pb films with arrays of fully perforated holes (antidots) and partially drilled holes (blind holes). Our results show that an array of blind holes, characterized by a thin superconducting bottom layer, gives rise to a less efficient pinning potential than an array of antidots. On top of that, a lower number of flux quanta trapped per pinning site (the saturation number), is observed for the blind hole array. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailAC susceptibility of superconducting films with a periodic pinning array
Silhanek, Alejandro ULg; Raedts, S.; Lange, M. et al

in Physica C: Superconductivity (2004), 408

We use AC-susceptibility measurements to study the dynamic response of vortices in a Pb thin film with a periodic array of antidots. In the linear regime, from the field dependence of the AC-penetration ... [more ▼]

We use AC-susceptibility measurements to study the dynamic response of vortices in a Pb thin film with a periodic array of antidots. In the linear regime, from the field dependence of the AC-penetration depth lambda we determine the curvature of the pinning potential well alpha for different matching fields. For applied fields H below the first matching field H-1, alpha reaches its highest value due to the strong vortex localization at the pinning sites. For H-1 < H < H-2, the metallic-like behavior of interstitial vortices gives rise to a reduction of alpha and a further decrease of the pinning strength is observed for H-2 < H < H-3. However, for H-3 < H < H-4, a reentrance in the pinning strength appears, due to a specific configuration of the flux line lattice which strongly restricts the mobility of vortices. [less ▲]

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See detailDynamic regimes in films with a periodic array of antidots
Silhanek, Alejandro ULg; Raedts, S.; Van Bael, M. J. et al

in European Physical Journal B -- Condensed Matter (2004), 37(1), 19-24

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T,H) measurements. At low enough ac drive amplitudes h, vortices moving inside the ... [more ▼]

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T,H) measurements. At low enough ac drive amplitudes h, vortices moving inside the pinning potential give rise to a frequency- and h-independent response together with a scarce dissipation. For higher amplitudes, the average distance travelled by vortices surpasses the pinning range and a critical state develops. We found that the boundary h*(H,T) between these regimes smoothly decreases as T increases whereas a step-like behavior is observed as a function of field. We demonstrate that these steps in h*(H) arise from sharp changes in the pinning strength corresponding to different vortex configurations. For a wide set of data at several fields and temperatures in the critical state regime, we show that the scaling laws based on the simple Bean model are satisfied. [less ▲]

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See detailIn-plane anisotropic vortex motion induced by a square array of antidots
Silhanek, Alejandro ULg; Van Look, L.; Raedts, S. et al

in Physica C: Superconductivity (2004), 404(1-4), 340-344

We report on electro-transport measurements on a Pb thin film with a square array of antidots, for the whole angular range of in-plane current orientations. We demonstrate that the interaction of a moving ... [more ▼]

We report on electro-transport measurements on a Pb thin film with a square array of antidots, for the whole angular range of in-plane current orientations. We demonstrate that the interaction of a moving flux line lattice with a periodic pinning potential, breaks the rotational symmetry and induces a guided vortex motion along the principal symmetry orientations of the pinning array. As a consequence, we found that for orientations different than the symmetry directions, the vortex velocity is not aligned with the Lorentz force. We show that this anisotropic vortex motion is temperature dependent and progressively fades out when approaching the normal state. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailGuided vortex motion in superconductors with a square antidot array
Silhanek, Alejandro ULg; Van Look, L.; Raedts, S. et al

in Physical Review. B : Condensed Matter (2003), 68(21),

We have measured the in-plane anisotropy of the vortex mobility in a thin Pb film with a square array of antidots. The Lorentz force, acting on the vortices, was rotated by adding two perpendicular ... [more ▼]

We have measured the in-plane anisotropy of the vortex mobility in a thin Pb film with a square array of antidots. The Lorentz force, acting on the vortices, was rotated by adding two perpendicular currents and keeping the amplitude of the net current constant. One set of voltage probes was used to detect the vortex motion. We show that the pinning landscape provided by the square antidot lattice influences the vortex motion in two different ways. First, the modulus of the vortex velocity becomes angular dependent with a lower mobility along the diagonals of the pinning array. Second, the vortex displacement is preferentially parallel to the principal axes of the underlying pinning lattice, giving rise to a misalignment between the vortex velocity and the applied Lorentz force. We show that this anisotropic vortex motion is temperature dependent and progressively fades out when approaching the normal state. [less ▲]

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See detailField-dependent vortex pinning strength in a periodic array of antidots
Silhanek, Alejandro ULg; Raedts, S.; Lange et al

in Physical Review. B : Condensed Matter (2003), 67(6),

We explore the dynamic response of vortex lines in a Pb thin film with a periodic array of antidots by means of ac-susceptibility measurements. For low drive field amplitudes, within the Campbell regime ... [more ▼]

We explore the dynamic response of vortex lines in a Pb thin film with a periodic array of antidots by means of ac-susceptibility measurements. For low drive field amplitudes, within the Campbell regime, vortex motion is of intravalley type and the penetration depth is related to the curvature of the pinning potential well alpha. For dc fields below the first matching field H-1, alpha reaches its highest value associated with a Mott insulator like phase where vortex lines are strongly localized at the pinning sites. For H-1<H-dc<H-2, the response is mainly due to the interstitial vortices and α drops to smaller values as expected for this metallic like regime. Strikingly, for H-2<H-dc<H-3, we observe that α reduces further down. However, for H-3<H-dc<H-4, a reentrance in the pinning strength is observed, due to a specific configuration of the flux-line lattice which strongly restricts the mobility of vortices. We present a possible explanation for the measured α(H-dc) dependence based on the different flux-line lattice configurations. [less ▲]

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