We report on the observation of the Pancharatnam-Berry phase in a condensate of indirect excitons (IXs) in a GaAs coupled quantum well structure. The Pancharatnam-Berry phase leads to phase shifts of interference fringes in IX interference patterns. Correlations are found between the phase shifts, polarization pattern of IX emission, and onset of IX spontaneous coherence. The Pancharatnam-Berry phase is acquired due to coherent spin precession in IX condensate. The effect of the Pancharatnam-Berry phase on the IX phase pattern is described in terms of an associated momentum.

We report the observation of spin currents in a coherent gas of indirect excitons. The realized long-range spin currents originate from the formation of a coherent gas of bosonic pairs — a new mechanism to suppress the spin relaxation. The spin currents result in the appearance of a variety of polarization patterns, including helical patterns, four-leaf patterns, spiral patterns, bell patterns, and periodic patterns. We demonstrate control of the spin currents by a magnetic field. We also present a theory of coherent exciton spin transport that describes the observed exciton polarization patterns and indicates the trajectories of the spin currents.

A.A. High, A.T. Hammack, J.R. Leonard, Sen Yang, L.V. Butov, T. Ostatnicky, M. Vladimirova, A.V. Kavokin, T.C.H. Liew, K.L. Campman, A.C. Gossard. Spin currents in a coherent exciton gas, arxiv:1302.3852 (2013), Phys. Rev. Lett. 110, 246403 (2013).

A.A. High, A.T. Hammack, J.R. Leonard, Sen Yang, L.V. Butov, T. Ostatnicky, A.V. Kavokin, A.C. Gossard, Spin Texture in a Cold Exciton Gas, arXiv:1103.0321v1 (2011).

A.A. High, J.R. Leonard, A.T. Hammack, Sen Yang, M.M. Fogler, L.V. Butov, T. Ostatnicky, M.R. Vladimirova, A.V. Kavokin, K.L. Campman, A.C. Gossard, Spontaneous Coherence in a Cold Exciton Gas, Spin Currents in a Coherent Exciton Gas, CLEO/QELS, May 7-11, 2012, San Jose, CA.

A.A. High,A.T. Hammack, J.R. Leonard, SenYang,L.V.Butov, T. Ostatnicky, A.V. Kavokin, A. C. Gossard, Spin Texture in a Cold Exciton Gas, APS March Meeting, March 21-25, 2011, Dallas, TX.

Spin transport of indirect excitons in GaAs/AlGaAs coupled quantum wells was observed by measuring the spatially resolved circular polarization of exciton emission. Exciton spin transport over several microns originates from a long spin relaxation time and long lifetime of indirect excitons.

J.R. Leonard, Y.Y. Kuznetsova, Sen Yang, L.V. Butov, T. Ostatnicky, A. Kavokin, and A.C. Gossard, Spin transport of excitons, arXiv:0905.2216v1, Nano Lett. 9 (12), 4204-4208 (2009).