Observation of Half-Quantum Vortices in an Exciton-Polariton Condensate
K. G. Lagoudakis, T. Ostatnicky, A. V. Kavokin, Y. G. Rubo, R. André and B. Deveaud-Plédran
Singly quantized vortices have already been observed in many systems, including the superfluid helium, Bose-Einstein condensates of dilute atomic gases, and condensates of exciton-polaritons in the solid state. Two-dimensional superfluids carrying spin are expected to demonstrate a different type of elementary excitations referred to as half-quantum vortices, characterized by a rotation of the phase and a rotation of the polarization vector when circumventing the vortex core. We detect half-quantum vortices in an exciton-polariton condensate by means of polarization-resolved interferometry, real-space spectroscopy, and phase imaging. Half-quantum vortices coexist with single-quantum vortices in our sample.