Magnetic flux in active and passive superconducting devices

Wördenweber, R.; Lahl, P.; Dymashevski, P.

doi:10.1016/s0921-4534(01)01232-1

Cited by 7 publications

(3 citation statements)

References 18 publications

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“…These systems rely essentially on either static arrays, such as pinning centers [2,3,4,5] and vortex-antivortex generators [6,7], or components influencing the vortex dynamics like channels [8,9,10,11] and ratchets [12,13]. The ultimate motivation behind the manipulation of the local vortex density is to enhance the performance of superconductor-based devices by reducing the noise in squid-based systems [14,15], gaining control on superconducting THz emitters [16] or even providing a way to predefine the optical transmission through the system [17].Unfortunately, for the majority of the components used in fluxonics devices, once they are created there is no margin for further modifications. In some cases this lack of flexibility becomes a limiting factor in the performance of the devices.…”

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confidence: 99%

Switchable magnetic dipole induced guided vortex motion

Verellen

Silhanek

Gillijns

et al. 2008

Applied Physics Letters

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We present evidence of magnetically controlled guided vortex motion in a hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of a square array of permalloy square rings. When the rings are magnetized with an in-plane external field H, an array of point-like dipoles with moments antiparallel to H, is formed. The resulting magnetic template generates a strongly anisotropic pinning potential landscape for vortices in the superconducting layer. Transport measurements show that this anisotropy is able to confine the flux motion along the high symmetry axes of the square lattice of dipoles. This guided vortex motion can be either re-routed by 90 degrees by simply changing the dipole orientation or even strongly suppressed by inducing a flux-closure magnetic state with very low stray fields in the rings. During the last years there has been a considerable effort to conceive and realize new superconducting devices that allow to modulate locally the magnetic fields practically at will [1]. These systems rely essentially on either static arrays, such as pinning centers [2,3,4,5] and vortex-antivortex generators [6,7], or components influencing the vortex dynamics like channels [8,9,10,11] and ratchets [12,13]. The ultimate motivation behind the manipulation of the local vortex density is to enhance the performance of superconductor-based devices by reducing the noise in squid-based systems [14,15], gaining control on superconducting THz emitters [16] or even providing a way to predefine the optical transmission through the system [17].Unfortunately, for the majority of the components used in fluxonics devices, once they are created there is no margin for further modifications. In some cases this lack of flexibility becomes a limiting factor in the performance of the devices. For instance, a predefined ratchet system designed to effectively remove vortices from a specific location can work properly at low fields but ignores the inevitable reversed ratchet at higher fields thus making its functionality rather impractical [12,13,18,19]. A way to circumvent this shortcoming can be worked out by introducing magnetic pinning centers which have additional internal degrees of freedom not available in conventional nanostructured pinning sites or defects created via irradiation.In this work we demonstrate that reversible and switchable guidance of the vortex motion can be achieved using a square array of magnetic square rings lying underneath a superconducting film. Transport measurements unambiguously show that the vortex dynamics is fully dominated by the magnetic landscape generated by the ring structures. When the magnetic unit cell is rotated 45 degrees off the Lorentz force F L the average vortex velocity v follows the direction of the principal axis of the magnetic lattice rather than the driving force. This channeling effect can be easily suppressed when inducing a nearly isotropic pinning landscape by setting the square rings in a flux-closure state with very low stray fields.The two samples used f...

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confidence: 99%

Switchable magnetic dipole induced guided vortex motion

Verellen

Silhanek

Gillijns

et al. 2008

Applied Physics Letters

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“…As an example the response of a coplanar [12,13] and a strip-line resonators [14,15], which are ones of mostly-used techniques for investigation of microwave response was calculated. The current distributions are J , OC 1 / J ( W 2 -x 2 ) ( a 2 -x 2 ) for coplanar resonator [12,13] ( W , a are the parameters of coplanar resonator) and J , oc 1 /JD for strip-line one [14,15].…”

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confidence: 99%

“…The current distributions are J , OC 1 / J ( W 2 -x 2 ) ( a 2 -x 2 ) for coplanar resonator [12,13] ( W , a are the parameters of coplanar resonator) and J , oc 1 /JD for strip-line one [14,15].…”

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confidence: 99%

The universal approach to calculation of the linear microwave response of thin superconducting films in perpendicular magnetic field with the trapped magnetic flux

Luzhbin

The Fifth International Kharkov Symposium on Physics and Engineering of Microwaves, Millimeter, and Submillimeter Waves (IEEE C

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The microwave response of thin superconducting films placed in the perpendicular magnetic field brings us the variety of unexpected phenomena in the dynamics of the mixed state of superconductors. The variety of dependences in the high-frequency response in nonlinear regime [ 1,2 and references therein] as well as in linear one [3,4] was measured in thin films of superconductors in a magnetic field. One of the features to be explained is the nonmonotonous dependence of the surface resistance (or quality factor or energy losses) on the static (linear response) or on the amplitude of high-frequency (nonlinear response) magnetic fields. The variety of experimental results [ 1-41 and theoretical approaches to explain them [4-6 and references therein] are still controversial and no any generally accepted mechanism of such behavior still exists. The general task of analysis of the experimental data is to distinguish between real physics of the vortex matter and some artificial experimental factors like geometry of sample, measurement methods etc.Laying aside the nonlinear response of superconductors the main attention in this work will be paid to the linear response of thin films in perpendicular magnetic field. The general method of calculation of energy losses caused by vortex motion in thin superconducting films placed in perpendicular magnetic field is proposed. As an example the responses of coplanar and strip-line resonators are calculated. The dependences calculated are compared with available experimental data.Theoretical consideration.Let us consider the thin superconducting film (infinitely long along they direction, with thickness d and width 2w , w >> d ) placed in a perpendicular dc magnetic field Bo (along the z-axis). Hereafter the film will be considered in the "one-dimensional" approximation, which means that all currents and fields are distributed only along the x-axis with some averaged along the z-axis values. This approach can be exploited for A [7,8]. The static magnetic field Bo generates the shielding current Jo(x) [7]:(some corrections need to be taken into account in order to avoid the divergence at the film's edges, see [ 131).The magnetic field trapped inside the film is concentrated in the region -b < x < b with some magnetic field distribution function B ( x ) [7,8]. The vortices trapped inside the film (the field B(x)) generate additional shielding current J , (x) : dt so that the magnetic field component perpendicular to the film's surface is nonzero only in the -b < x < b region.The external ac field generates shielding current J $ ( x ) inside the film. This current forces the vortices to oscillate with the same frequency o as the ac field. Vortices located in some Ax region move under that force on a distance u ( x ) leading to the change in the magnetic field distribution inside the film: 0-7803-841 1-3/04/$20.0002004 IEEE 433

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Four coplanar superconducting strips: flux-focusing effects and inductance

Brojeny

Clem

2004

Supercond. Sci. Technol.

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We present analytic solutions for the Meissner-state magnetic-field and current-density distributions for four long parallel coplanar superconducting strips carrying subcritical currents in a perpendicular magnetic field when there is no net magnetic flux through the two slots between the outermost strips. We make use of these solutions to investigate the flux-focusing effect; i.e., we calculate how much magnetic flux per unit length is focused into the central slot when the strips are in a perpendicular magnetic field Ha = Ba/μ0 and the outermost pairs of strips carry no net current. We also calculate the inductance per unit length of the system when the net current flowing in the two right strips is equal in magnitude and but opposite in direction to the net current flowing in the two left strips. We show that for narrow superconducting strips mutual-inductance calculations based on exact results for two strips provide good approximations to our exact results for four strips.

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Magnetic flux in active and passive superconducting devices

Cited by 7 publications

References 18 publications

Switchable magnetic dipole induced guided vortex motion

Switchable magnetic dipole induced guided vortex motion

The universal approach to calculation of the linear microwave response of thin superconducting films in perpendicular magnetic field with the trapped magnetic flux

Four coplanar superconducting strips: flux-focusing effects and inductance

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