Chiral emission induced by optical Zeeman effect in polariton micropillars

The low sensitivity of photons to external magnetic fields is one of the major challenges for the engineering of photonic lattices with broken time-reversal symmetry. We show experimentally that time-reversal symmetry can be broken for microcavity polaritons in the absence of any external magnetic field thanks to polarization dependent polariton interactions. Circularly polarized excitation of carriers in a micropillar induces a Zeeman-like energy splitting between polaritons of opposite polarizations. In combination with optical spin-orbit coupling inherent to semiconductor microstructures, the interaction-induced Zeeman splitting results in emission of vortex beams with a well-defined chirality. Our experimental findings can be extended to lattices of coupled micropillars opening the possibility of controlling by optical means the topological properties of polariton Chern insulators.