Spin multistability of cavity polaritons in a magnetic field
  Spin transitions are studied theoretically and experimentally in a resonantly excited system of cavity polaritons in a magnetic field. Weak pair interactions in this boson system make possible fast and massive spin flips occurring at critical amplitudes due to the interplay between amplitude dependent shifts of eigenstates and the Zeeman splitting. Dominant spin of a condensate can be toggled forth and back by tuning of the pump intensity only, which opens the way for ultra-fast spin switchings of polariton condensates on a picosecond timescale. 
S. S. Gavrilov, A. V. Sekretenko, N. A. Gippius, C. Schneider, S.   H\"ofling, M. Kamp, A. Forchel, V. D. Kulakovskii
cond-mat.mes-hall physics.optics