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Semiconductor Microcavities Galore

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The possibility of high temperature Bose Einstein condensation (BEC) in the solid state offers an attractive alternative to ultracold atomic BEC . Polaritons in semiconductor microcavities, the admixture of an exciton and a cavity photon in the strong coupling regime, are currently on the frontline of research in this field. Due to their photon component, the de Broglie wavelength of polaritons is several orders of magnitude larger than that of atoms, allowing in principle for BEC even at room temperature. However, unlike atoms, the polariton lifetime is limited by the photon cavity lifetime to a few picoseconds. Although the ultrashort lifetime prevents thermalisation with the host lattice, inter-particle interactions allow for rapid relaxation and formation of a macroscopically occupied ground state, usually referred to as polariton condensate. In this seminar, we will discuss different configurations of polariton condensation both in 2D and pillar microcavities. The transient formation of polariton condensation in a 2D GaAs/AlAs semiconductor microcavity under non-resonant pulsed optical excitation and the transition from the weak- to the strong-coupling regime at high excitation densities in the time domain will be analysed. In pillar microcavities the observation of non-ground state polariton condensation and the kinetics that produce such state will be discussed. Finally we will discuss the Optical Spin Hall Effect another interesting property of microcavity-polaritons that was shown to allow the separation of spin polarized carriers in real and momentum space. Although the effect was previously attributed to the mixed photonic and excitonic polariton character, we have been able to observe this effect in a bare photonic cavity. Fig 1: Near-(a) and far-field(b) separation of photons based on their spin in an all-optical microcavity.

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