Suppression of superfluidity of exciton-polaritons by magnetic field

We show that the properties of exciton-polariton condensate in a semiconductor microcavity are strongly sensitive to the external magnetic field normal to the cavity plane. In particular, the superfluidity is suppressed at a critical magnetic field B-c proportional to the polariton concentration. For B < B-c the Zeeman splitting of polaritons is exactly compensated by polariton-polariton interactions in the elliptically polarized condensate. Above the critical point, the spin degeneracy is lifted and the superfluidity reappears again on the circularly polarized lower polariton branch. (c) 2006 Elsevier B.V. All rights reserved.