In superconductivity, a Josephson vortex (after

Brian Josephson Brian David Josephson (born 4 January 1940) is a Welsh theoretical physicist and professor emeritus of physics at the University of Cambridge. Best known for his pioneering work on superconductivity and quantum tunnelling, he was awarded the ...

from Cambridge University) is a

quantum vortex In physics, a quantum vortex represents a quantized flux circulation of some physical quantity. In most cases, quantum vortices are a type of topological defect exhibited in superfluids and superconductors. The existence of quantum vortices was ...

of supercurrents in a

Josephson junction In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mec ...

(see

Josephson effect In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mec ...

). The supercurrents circulate around the vortex center which is situated inside the Josephson barrier, unlike

Abrikosov vortices In superconductivity, fluxon (also called a Abrikosov vortex and quantum vortex) is a vortex of supercurrent in a type-II superconductor, used by Alexei Abrikosov to explain magnetic behavior of type-II superconductors. Abrikosov vortices occu ...

type-II superconductors In superconductivity, a type-II superconductor is a superconductor that exhibits an intermediate phase of mixed ordinary and superconducting properties at intermediate temperature and fields above the superconducting phases. It also features the ...

, which are located in the superconducting condensate.

(after Alexei Abrikosov) in superconductors are characterized by normal cores where the superconducting condensate is destroyed on a scale of the superconducting

coherence length In physics, coherence length is the propagation distance over which a coherent wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves dif ...

''ξ'' (typically 5-100 nm) . The cores of Josephson vortices are more complex and depend on the physical nature of the barrier. In Superconductor-Normal Metal-Superconductor (SNS)

Josephson junctions In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mech ...

there exist measurable superconducting correlations induced in the N-barrier by

proximity effect Proximity effect may refer to: * Proximity effect (atomic physics) * Proximity effect (audio), an increase in bass or low frequency response when a sound source is close to a microphone * ''Proximity Effect'' (comics), a comic book series written by ...

from the two neighbouring superconducting electrodes. Similarly to Abrikosov vortices in superconductors, Josephson vortices in SNS

are characterized by cores in which the correlations are suppressed by destructive quantum interference and the normal state is recovered. However, unlike Abrikosov cores, having a size ~''ξ'', the size of the Josephson ones is not defined by microscopic parameters only. Rather, it depends on supercurrents circulating in superconducting electrodes, applied magnetic field etc. In Superconductor-Insulator-Superconductor (SIS) Josephson tunnel junctions the cores are not expected to have a specific spectral signature; they were not observed. Usually the Josephson vortex's supercurrent loops create a magnetic flux which equals, in long enough Josephson junctions, to Φ₀—a single flux quantum. Yet

fractional vortices In a standard superconductor, described by a complex field fermionic condensate wave function (denoted , \Psi, e^), vortices carry quantized magnetic fields because the condensate wave function , \Psi, e^ is invariant to increments of the phase \ph ...

may also exist in Superconductor-Ferromagnet-Superconductor

or in junctions in which superconducting phase discontinuities are present. It was demonstrated by Hilgenkamp et al. that Josephson vortices in the so-called ''0-π'' Long Josephson Junctions can also carry half of the flux quantum, and are called

semifluxon In superconductivity, a semifluxon is a half integer vortex of supercurrent carrying the magnetic flux equal to the half of the magnetic flux quantum . Semifluxons exist in the 0-π long Josephson junctions at the boundary between 0 and π region ...

s. It has been shown that under certain conditions a propagating Josephson vortex can initiate another Josephson vortex. This effect is called flux cloning (or fluxon cloning). Although a second vortex appears, this does not violate the conservation of the single flux quantum.

References

{{DEFAULTSORT:Josephson Vortex Josephson effect Vortices

See also

References