Edge effect pinning in mesoscopic superconducting strips with non-uniform distribution of defects

February 11, 2019

In a study published in Scientific Reports, researchers determined the spatial distribution of the defects optimizing the critical current and found that it is in general non-uniform and asymmetric.

(a) Two-dimensional superconducting strip of width W = 64ξ with non-homogeneous inclusion distribution. The current J is applied vertically (along the x-axis), the magnetic field B is perpendicular to the figure plane, and the resulting Lorentz force FL acts to the right (along the y-axis). The sample has a length of L = 1024ξ with quasi-periodic boundary conditions in the x direction; in the y direction, we have open boundary conditions, i.e., superconductor-vacuum surfaces. The strip contains (uncorrelated) randomly placed circular inclusions of diameter d = 3ξ. The density of these inclusions depends on y: in the middle of the sample, the volume fraction occupied by inclusions is f = 0.2, which corresponds approximately to conditions for the maximum possible critical current density in bulk samples. The density of the inclusion ρi(y) decreases linearly near the sample boundaries (see bottom plot): within a region of width lin at the boundary where vortices enter the sample and lout at the boundary where vortices leave the sample. (b) The critical current Jc as a function of lin and lout normalized by Jc(0, 0) at applied magnetic field B = 0.1Hc2. The critical current is increased by ~30% for finite lin and lout compared to the critical current from a homogeneous defect distribution (lin = lout = 0). The values of lin and lout corresponding to the maximum of the critical current Jc(lin, lout) are shown by colored circles for B = 0.1Hc2, 0.2Hc2, and 0.3Hc2. The effect is asymmetric and depends on the direction of vortex motion. The maximum is indicated by a (blue) circle. Corresponding maxima for fields 0.2Hc2 and 0.3Hc2 are indicated by (cyan and green) circles, marked by the field value.

Scientific Achievement

Gained insight into the interplay between bulk pinning and edge barriers for vortex transport in mesoscopic superconducting strips and bridges.

Significance and Impact

Developed recipes to optimize configuration of the bulk pinning for the best performance.

Research Details

Utilized large-scale time-dependent Ginzburg-Landau simulations of heterogenous pinning landscapes.
Strategic defect distribution dramatically increases critical current in mesoscopic super-conducting strips.
Uncovered the non-additive nature of geometrical and bulk pinning

DOI: 10.1038/s41598-018-36285-4

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