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High A.A.,University of California at San Diego | Hammack A.T.,University of California at San Diego | Leonard J.R.,University of California at San Diego | Yang S.,University of California at San Diego | And 9 more authors.
Physical Review Letters | Year: 2013

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. © 2013 American Physical Society. Source


Savenko I.G.,University of Iceland | Savenko I.G.,Nanyang Technological University | Liew T.C.H.,Nanyang Technological University | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | And 2 more authors.
Physical Review Letters | Year: 2013

We present a theory for the description of energy relaxation in a nonequilibrium condensate of bosonic particles. The approach is based on coupling to a thermal bath of other particles (e.g., phonons in a crystal, or noncondensed atoms in a cold atom system), which are treated with a Monte Carlo type approach. Together with a full account of particle-particle interactions, dynamic driving, and particle loss, this offers a complete description of recent experiments in which Bose-Einstein condensates are seen to relax their energy as they propagate in real space and time. As an example, we apply the theory to the solid-state system of microcavity exciton polaritons, in which nonequilibrium effects are particularly prominent. © 2013 American Physical Society. Source


Ohadi H.,University of Southampton | Kammann E.,University of Southampton | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | Lagoudakis K.G.,Stanford University | And 3 more authors.
Physical Review Letters | Year: 2012

We report on the simultaneous observation of spontaneous symmetry breaking and long-range spatial coherence both in the strong- and the weak-coupling regime in a semiconductor microcavity. Under pulsed excitation, the formation of a stochastic order parameter is observed in polariton and photon lasing regimes. Single-shot measurements of the Stokes vector of the emission exhibit the buildup of stochastic polarization. Below threshold, the polarization noise does not exceed 10%, while above threshold we observe a total polarization of up to 50% after each excitation pulse, while the polarization averaged over the ensemble of pulses remains nearly zero. In both polariton and photon lasing regimes, the stochastic polarization buildup is accompanied by the buildup of spatial coherence. We find that the Landau criterion of spontaneous symmetry breaking and Penrose-Onsager criterion of long-range order for Bose-Einstein condensation are met in both polariton and photon lasing regimes. © 2012 American Physical Society. Source


Matuszewski M.,Instytut Fizyki Polskiej Akademii Nauk | Liew T.C.H.,National Autonomous University of Mexico | Liew T.C.H.,Mediterranean Institute of Fundamental Physics | Rubo Y.G.,National Autonomous University of Mexico | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We calculate the spatial structure of four-component spinor systems of mixed bright and dark exciton condensates in coupled quantum wells. The spin-dependent bright-dark exciton conversion and Dresselhaus spin-orbit coupling is found to generate a rich variety of topological elements. By propagating the Gross-Pitaevskii equation in imaginary time, we observe the following: single and multiple polarized vortices; the phase separation of bright and dark excitons; and exotic spatial structures in density and spin polarization. ©2012 American Physical Society. Source


Liew T.C.H.,Mediterranean Institute of Fundamental Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A concept of complex reflectivity modulation is proposed based on the electrical control of quantum well exciton resonances that influence the propagation of light in a layered semiconductor structure. By variation in exciton energies, both the intensity and the phase of reflected light can be fully controlled. Unlike previous devices, for full complex light modulation, the design is based on a single device in a single structure. The device allows complete 100% intensity contrast and allows for the construction of small pixel sizes with fast response times. © 2012 American Physical Society. Source

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