Semifluxons exist in the 0-π long Josephson junctions at the boundary between 0 and π regions.
Mathematically, a semifluxon can be constructed by joining two tails of conventional (integer) fluxon (kink of the sine-Gordon equation) at the 0-π boundary.
For the first time the semifluxons were observed at the tricrystal grain boundaries in d-wave superconductors[3] and later in YBa2Cu3O7–Nb ramp zigzag junctions.
[4] In these systems the phase shift of π takes place due to d-wave order parameter symmetry in YBa2Cu3O7 superconductor.
Further, physicists were able to demonstrate a molecule made of two interacting semifluxons arranged antiferromagnetically.