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CM-AMO Seminar<br>Bose-Einstein Condensation (BEC) and Polariton Lasing in ZnO Microcrystallines<br><b>Speaker: Xiangshun Lu (University of Arkansas)</b>

Tuesday, November 29, 2011
12:00 AM
335 West Hall

Speaker: Xiangshun Lu (University of Arkansas)

Bose-Einstein condensation (BEC) has fascinated scientists for decades and has been observed in atomic gases and solid-state materials. Due to their small effective mass, exciton-polaritons in semiconductor microcavities have been regarded as the most promising candidates to generate BEC even above room temperature¬. Since exciton-polaritons have lower-polariton branch (LPB) and upper-polariton branch (UPB), in principle, BEC should be formed in both branches. In the presentation, I will show you the observation of exciton-polaritons on ZnO nanowire and nanowires-based microcrystallines, and their direct mapping to the dispersion curves at low pumping power when the second harmonic photons are in resonance with the excitons. When the pumping power is increased above a critical threshold, we observed BEC and polariton lasing on both LPB and UPB. Various evidences of confirming BEC will be addressed, which include the appearance of interference fringes formed by the long-range spatial spontaneous coherence, a spectroscopic accumulation to the lowest energy state in momentum space, a linear polarization buildup, a superlinear increase of intensity, and the spatial and spectral narrowing features.