Flux distribution in superconducting films with holes

Vestgården, Jørn Inge; Shantsev, D. V.; Galperin, Y. M.; Johansen, T. H.

doi:10.1103/physrevb.77.014521

Cited by 36 publications

(32 citation statements)

References 33 publications

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“…For example, it has been reported that patterning with regular arrays of antidots makes the magnetic flux penetration anisotropic [8,10]. Currently, there are only few numerical simulation works that has considered the critical state flux penetration in samples patterned with antidots [9,11,[51][52][53][54]. In order to improve the theoretical knowledge on the field, we will here consider the numerically challenging sample configuration of a superconducting ring patterned with a square array of disc-shaped antidots.…”

Section: Film With Antidotsmentioning

confidence: 99%

Nonlocal electrodynamics of normal and superconducting films

Vestgården¹,

Mikheenko²,

Galperin³

et al. 2013

New J. Phys.

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Electrically conducting films in a time-varying transverse applied magnetic field are considered. Their behavior is strongly influenced by the self-field of the induced currents, making the electrodynamics nonlocal, and consequently difficult to analyze both numerically and analytically. We present a formalism which allows many phenomena related to superconducting and Ohmic films to be modeled and analyzed. The formalism is based on the Maxwell equations and a material current-voltage characteristics, linear for normal metals and nonlinear for superconductors, plus a careful account of the boundary conditions. For Ohmic films, we consider the response to a delta function sourcefield turned on instantly. As one of few problems in nonlocal electrodynamics, this has an analytical solution, which we obtain in both Fourier and real space. Next, the dynamical behavior of a square superconductor film during ramping up of the field, and subsequently returning to zero, is treated numerically. Then, this remanent state is used as initial condition for triggering thermomagnetic nonlocality implies that induced currents flow in the entire sample [3,4]. Thus, the film behavior is qualitatively different from that of bulks, and magneto-optical imaging (MOI) of thin superconductors has revealed strong piling up of the magnetic field around the sample edges, where values far above H a are reached [5]. At internal boundaries, such as the inner edge of a planar ring, the field can, due to the nonlocal electrodynamics, be in the opposite direction of the applied field [6,7]. Strongly modified behavior is found also in films patterned with regular arrays of small holes (antidots), which tend to guide the flux into the superconductor [8][9][10][11].The response of Ohmic films exposed to varying transverse magnetic fields is also described by nonlocal electrodynamics, but here the material responds linearly. Numerical solutions for strip and disc geometries have shown that the combination of nonlocality and dissipation causes a rapid penetration of a suddenly applied magnetic field [12,13]. Different from superconductors, even regions deep inside an Ohmic film are quickly penetrated by the magnetic field.A phenomenon that involves both the critical-state and Ohmic properties is the occurrence of flux avalanches or flux jumps. These are commonly observed in type-II superconductors at low temperatures, and are caused by a thermomagnetic instability which drives the superconductor from the critical-state to a high resistivity state [14]. The instability is triggered, e.g. by a small temperature fluctuation which reduces the flux pinning locally, and some quantized flux lines, or vortices, will start moving. This creates local heat dissipation and the temperature will increase even further, thus forming a positive feedback loop. The result can be an exponential growth in the temperature and a large-scale runaway of magnetic flux. In superconducting films the thermomagnetic instability is seen by MOI to manifest as abrupt avalanches of mag...

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Section: Film With Antidotsmentioning

confidence: 99%

Nonlocal electrodynamics of normal and superconducting films

Vestgården¹,

Mikheenko²,

Galperin³

et al. 2013

New J. Phys.

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“…Hence, the current density quickly rises to the critical value, causing major rearrangements of both the current flow and the flux distribution. 22 Magneto-optical imaging (MOI) is a unique experimental tool for observing the nontrivial redistributions created by patterning of superconducting films. The technique allows direct observation of the flux density over length scales ranging from the entire sample size and down to the size of individual antidots.…”

Section: Introductionmentioning

confidence: 99%

Mechanism for flux guidance by micrometric antidot arrays in superconducting films

et al. 2012

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Abstract"A study of magnetic flux penetration in a superconducting film patterned with arrays of micron-sized antidots (microholes) is reported. Magneto-optical imaging (MOI) of a YBa(2)Cu(3)O(x) film shaped as a long strip with perpendicular antidot arrays revealed both strong guidance of flux and, at the same time, large perturbations of the overall flux penetration and flow of current. These results are compared with a numerical flux creep simulation of a thin superconductor with the same antidot pattern. To perform calculations on such a complex geometry, an efficient numerical scheme for handling the boundary conditions of the antidots and the nonlocal electrodynamics was developed. The simulations reproduce essentially all features of the MOI results. In addition, the numerical results give insight into all other key quantities (e. g., the electrical field), which become extremely large in the narrow channels connecting the antidots." A study of magnetic flux penetration in a superconducting film patterned with arrays of micron-sized antidots (microholes) is reported. Magneto-optical imaging (MOI) of a YBa 2 Cu 3 O x film shaped as a long strip with perpendicular antidot arrays revealed both strong guidance of flux and, at the same time, large perturbations of the overall flux penetration and flow of current. These results are compared with a numerical flux creep simulation of a thin superconductor with the same antidot pattern. To perform calculations on such a complex geometry, an efficient numerical scheme for handling the boundary conditions of the antidots and the nonlocal electrodynamics was developed. The simulations reproduce essentially all features of the MOI results. In addition, the numerical results give insight into all other key quantities (e.g., the electrical field), which become extremely large in the narrow channels connecting the antidots.

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“…Local magnetic field measurements were carried out via scanning Hall probe microscopy (SHPM) near the sample's border. It is important to remark that although previous works have shown spatially resolved flux penetration in bulk and thin films, 19 the power of SHPM allows us to determine unambiguously the flux penetration with unprecedented resolution of a single vortex.…”

Section: Sample Detailsmentioning

confidence: 99%

First vortex entry into a perpendicularly magnetized superconducting thin film

et al. 2013

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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 H c1 . However, the actual first flux penetration does not occur at H c1 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.

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Flux distribution in superconducting films with holes

Cited by 36 publications

References 33 publications

Nonlocal electrodynamics of normal and superconducting films

Nonlocal electrodynamics of normal and superconducting films

Mechanism for flux guidance by micrometric antidot arrays in superconducting films

First vortex entry into a perpendicularly magnetized superconducting thin film

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