Probing the collective excitations of a spinor polariton fluid

M.V.R. gratefully acknowledges support in the form of a Ph.D. fellowship of the Research Foundation–Flanders (FWO). M.W. acknowledges financial support from the FWO-Odysseus program. F.M.M. acknowledges financial support from the Ministerio de Economiaa y Competitividad (MINECO) (Contract No. MAT2011-22997) and the Comunidad Autonoma de Madrid (CAM) (Contract No. S-2009/ESP-1503)