  We report stable orthogonally polarised domains in high-density polariton
solitons propagating in a semiconductor microcavity wire. This effect arises
from spin dependent polariton-polariton interactions and pump-induced imbalance
of polariton spin populations. The interactions result in an effective magnetic
field acting on polariton spin across the soliton profile, leading to the
formation of polarisation domains. Our experimental findings are in excellent
agreement with theoretical modelling taking into account these effects.
