Fractional Vortices

Fractional Vortices

In a standard superconductor, described by a complex field (condensates wave function), vortices carry quantized magnetic field: a consequence of -invariance of the phase of the condensate wave function . There a winding of the phase by creates a vortex which carries one flux quantum. See Quantum vortex.

The term Fractional vortex is used for two kinds of very different quantum vortices which occur when:

(i) A physical system allows phase windings different from . I.e. non-integer or fractional phase winding. Quantum mechanics prohibits it in a uniform ordinary superconductor. But it becomes possible in an inhomogeneous system for example if a vortex is placed on a boundary between two superconductors which are connected only by an extremely weak link (also called Josephson Junction), such a situation also occurs in some cases in polycrystalline samples on grain boundaries etc. At such superconducting boundaries the phase can have a discontinous jump. Correspondingly a vortex placed onto such a boundary acquires a fractional phase windings hence the term fractional vortex. Similar situation occurs in Spin-1 Bose condensates where, a vortex with phase winding can exist if it is combined with a domain of overturned spins.

(ii) Different situation occurs in uniform multicomponent superconductors which allow stable vortex solution with integer phase winding, where which however carry arbitrarily fractionally quantized magnetic flux.