We observe a spontaneous parity breaking bifurcation to a ferromagnetic state
in a spatially trapped exciton-polariton condensate. At a critical bifurcation
density under nonresonant excitation, the whole condensate spontaneously
magnetizes and randomly adopts one of two elliptically polarized (up to 95%
circularly-polarized) states with opposite handedness of polarization. The
magnetized condensate remains stable for many seconds at 5 K, but at higher
temperatures it can flip from one magnetic orientation to another. We optically
address these states and demonstrate the inversion of the magnetic state by
resonantly injecting 100-fold weaker pulses of opposite spin. Theoretically,
these phenomena can be well described as spontaneous symmetry breaking of the
spin degree of freedom induced by different loss rates of the linear
polarizations.This work was supported by Grants EPSRC No. EP/G060649/1, EU No. CLERMONT4 235114, EU No. INDEX 289968, Spanish MEC (MAT2008-01555), Greek GSRT ARISTEIA Apollo program and Fundación La Caixa, and Mexican CONACYT No. 251808. FP acknowledges financial support through an EPSRC doctoral prize fellowship at the University of Cambridge and a Schrödinger fellowship at the University of Oxford.This is the final version of the article. It first appeared from the American Physical Society via http://dx.doi.org/10.1103/PhysRevX.5.03100
