Bose-Einstein condensation of exciton polaritons. by Kasprzak, J, Richard, M, Kundermann, S, Baas, A, Jeambrun, P, Keeling, J, Marchetti, F, Szymańska, M, André, R, Staehli, J, Savona, V, Littlewood, P, Deveaud, B, Dang, L