Regensburg 2013 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 55: Focus Session: Functionalized semiconductor nanowires II (DS, jointly with HL)

HL 55.2: Talk

Wednesday, March 13, 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 E_R are occupied. As the polariton-branch separation Δ E_P increases for lower mode numbers, the condensate gains kinetic energy when Δ E_P > Δ E_R. The lowermost state which can be reached is determined by the coupling strength and the lifetimes of exciton and WGM photon.