Vortex stability and permanent flow in nonequilibrium polariton condensates.

We study the effects of imprinting a single-quantized vortex on the steady state of a microcavity exciton-polariton condensate generated via parametric scattering. Interestingly we observe two distinct regimes: In the first case, at low polariton densities, the effect of the pulsed probe, containing the vortex state, is to generate a gain response in the condensate lasting for tens of picoseconds during which no dissipation of the circulating currents is detected. In the second regime, at higher densities, the gain lasts much less and the circulation is imprinted directly into the steady state, which acquires permanent rotation for as long as the vortex remains within the condensate. We use two different ways of measuring the circulation of the condensate and demonstrate that in both cases, polariton condensation in the parametric scattering regime can sustain permanent supercurrents. [ABSTRACT FROM AUTHOR]