Parametric inversion of spin currents in semiconductor microcavities

The optical spin-Hall effect results in the formation of an antisymmetric real-space polarization pattern giving birth to spin currents. In this work, we show that the exciton-polariton parametric scattering allows us to reverse the sign of these currents. We describe the pulsed resonant excitation of a strongly coupled microcavity with a linearly polarized pump at normal incidence. The energy of the pulse is set to be close to the inflexion point of the lower polariton dispersion branch and the focusing in real space populates the reciprocal space on a ring. Above threshold, the parametric scattering towards the idler and the signal state is triggered on the whole elastic circle. The injected particles are scattered toward these states while propagating radially all over the plane, gaining a cross-linear polarization with respect to that of the pump during the nonlinear process. Consequently, the propagation of the polaritons within the effective magnetic field results in the optical spin-Hall effect, with inverted polarization domains. DOI: 10.1103/PhysRevB.87.075316