In
superconductivity
Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlik ...
, 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 f ...
of
supercurrent
A supercurrent is a superconducting current, that is, electric current which flows without dissipation in a superconductor. Under certain conditions, an electric current can also flow without dissipation in microscopically small non-superconductin ...
s 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 me ...
). The supercurrents circulate around the vortex center which is situated inside the Josephson barrier, unlike
Abrikosov vortices in
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.
Abrikosov vortices (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 diff ...
''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 mec ...
there exist measurable superconducting correlations induced in the N-barrier by
proximity effect from the two neighbouring superconducting electrodes. Similarly to Abrikosov vortices in superconductors, Josephson vortices in 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 mec ...
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 Φ
0—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 \p ...
may also exist in Superconductor-Ferromagnet-Superconductor
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 mec ...
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 regions ...
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.
See also
*
Fluxon
*
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 me ...
*
Josephson penetration depth
*
Long Josephson junction
*
Shape waves
*
Sine-Gordon equation
References
{{DEFAULTSORT:Josephson Vortex
Josephson effect
Vortices