Abrikosov vortex

Vortices in a 200-nm-thick YBCO film imaged by scanning SQUID microscopy^[1]

In superconductivity, an Abrikosov vortex is a vortex of supercurrent in a type-II superconductor theoretically predicted by Alexei Abrikosov in 1957.^[2] The supercurrent circulates around the normal (i.e. non-superconducting) core of the vortex. The core has a size $\sim \xi$ — the superconducting coherence length (parameter of a Ginzburg-Landau theory). The supercurrents decay on the distance about $\lambda$ (London penetration depth) from the core. Note that in type-II superconductors $\lambda >\xi /{\sqrt {2}}$ . The circulating supercurrents induce magnetic fields with the total flux equal to a single flux quantum $\Phi_0$ . Therefore, an Abrikosov vortex is often called a fluxon.

The magnetic field distribution of a single vortex far from its core can be described by

B(r)={\frac {\Phi _{0}}{2\pi \lambda ^{2}}}K_{0}\left({\frac {r}{\lambda }}\right)\approx {\sqrt {{\frac {\lambda }{r}}}}\exp \left(-{\frac {r}{\lambda }}\right),

where $K_{0}(z)$ is a zeroth-order Bessel function. Note that, according to the above formula, at $r\to 0$ the magnetic field $B(r)\propto \ln(\lambda /r)$ , i.e. logarithmically diverges. In reality, for $r\lesssim \xi$ the field is simply given by

B(0)\approx {\frac {\Phi _{0}}{2\pi \lambda ^{2}}}\ln \kappa ,

where κ = λ/ξ is known as the Ginzburg-Landau parameter, which must be $\kappa >1/{\sqrt {2}}$ in type-II superconductors.

Abrikosov vortices can be trapped in a type-II superconductor by chance, on defects, etc. Even if initially type-II superconductor contains no vortices, and one applies a magnetic field $H$ larger than the lower critical field $H_{{c1}}$ (but smaller than the upper critical field $H_{{c2}}$ ), the field penetrates into superconductor in terms of Abrikosov vortices. Each vortex carries one thread of magnetic field with the flux $\Phi_0$ . Abrikosov vortices form a lattice, usually triangular, with the average vortex density (flux density) approximately equal to the externally applied magnetic field. As with other lattices, defects may form as dislocations.

References

↑ Wells, Frederick S.; Pan, Alexey V.; Wang, X. Renshaw; Fedoseev, Sergey A.; Hilgenkamp, Hans (2015). "Analysis of low-field isotropic vortex glass containing vortex groups in YBa₂Cu₃O_7−x thin films visualized by scanning SQUID microscopy". Scientific Reports. 5: 8677. PMC 4345321 . PMID 25728772. doi:10.1038/srep08677.
↑ Abrikosov, A. A. (1957). The magnetic properties of superconducting alloys. Journal of Physics and Chemistry of Solids, 2(3), 199-208.

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Abrikosov vortex

See also

References