Regensburg 2013 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 55: Focus Session: Functionalized semiconductor nanowires II (DS, jointly with HL)
HL 55.2: Vortrag
Mittwoch, 13. März 2013, 12:00–12:15, H8
BEC relaxation in a multimodal whispering-gallery exciton-polariton system — •Christof P. Dietrich, Tom Michalsky, Chris Sturm, Helena Franke, Martin Lange, Rüdiger Schmidt-Grund, and Marius Grundmann — Universität Leipzig, Inst. für Experimentelle Physik II, Linnéstr. 5, 04103 Leipzig
We present one-dimensional Bose-Einstein condensates (BEC) of whispering gallery mode (WGM) exciton-polaritons in ZnO-microwires up to room temperature. We show massive occupation of the bosonic ground state at condensation threshold, its blueshift and the condensate’s one-dimensional extension and spatial coherence. We find that the condensation mechanism is different from that observed in common (two-dimensional) Fabry-Perot microcavities since the WGM system provides numerous photonic modes. Its ground state is energetically far below the exciton transition, so the system is multimodal without polariton ground state. This leads to two effects: 1.) At room temperature, the scattering of reservoir polaritons into zero-momentum states is strongly assisted by LO-phonons and very efficient because the energy-momentum conservation can be very easily fulfilled. 2.) At low temperature, a parametric relaxation process of polaritons into lower polariton branches is observed when an occupation of one is reached. States with a fixed energy difference Δ ER are occupied. As the polariton-branch separation Δ EP increases for lower mode numbers, the condensate gains kinetic energy when Δ EP > Δ ER. The lowermost state which can be reached is determined by the coupling strength and the lifetimes of exciton and WGM photon.