  Polarization textures of light may reflect fundamental phenomena such as
topological defects, and can be utilized in engineering light beams. Three main
routes are applied during their creation: spontaneous appearance in phase
transitions, steering by an excitation beam, or structural engineering of the
medium. We present an approach that uses all three in a platform offering
advantages that are not simultaneously provided in any previous system:
advanced structural engineering, strong-coupling condensate with effective
photonic interactions, as well as room temperature and sub-picosecond
operation. We demonstrate domain wall polarization textures in a plasmonic
lattice Bose-Einstein condensate, by combining the dipole structure of the
lattice with a non-trivial condensate phase revealed by phase retrieval. These
results open new prospects for fundamental studies of non-equilibrium
condensation and sources of polarization-structured beams.
