In the field of polariton physics, ZnO has attracted a large attention due to it large exciton binding energy and oscillator strength, that enable to observe strong coupling at room temperature. We have recently demonstrated polariton condensation in such a cavity presenting a large quality factor (>2000) [1]. In the present work, we study the time-resolved spectroscopy of the polariton emission in this cavity, in order to assess the critical parameters of the polariton dynamics and their temperature dependance. We also study the theoretical model for the dynamics of microcavity polaritons. Figure 1 presents the experimental study of the photoluminescence dynamics of cavity polaritons. The measured exciton lifetime is about 50ps at 80K and at exciton densities close to the condensation threshold. It is rather independent of the temperature. It also governs the decay of each polariton branch fed by the exciton reservoir. Our modeling clarifies the time-constants involved in the exciton and polariton dynamics. In particular, we address the problem of the relative efficiencies of exciton formation assisted by either optical longitudinal phonons (LO) or acoustic phonons, and the following relaxation towards the polariton branches. We resolve the classical Boltzmann equation [2] which describes the relaxation kinetics of bosonic polariton. The energy relaxation rates of heated excitons due to emission and absorption of phonons have been calculated as a function of the lattice temperature. References [1] F. Li et al., Phys. Rev. Lett. 110, 196406 (2013) [2] G.Malpuech et al., Phys. Rev. B. 65,153310 (2002)

Spatial observation and optical manipulation of polariton quantum liquids are raising a large interest in the studies of polariton condensates inmicrocavities [1]. In this work, we report the study of polariton propagation in a full hybrid ZnO microcavity where the condensation of polaritons up to room temperature has recently been achieved [2]. One particularity of this cavity is its thickness gradient, allowing the access to a large range of exciton-photon detunings. This thickness gradient is also interesting because it creates a dragging force for polaritons and polariton condensates. It is therefore important to measure the spatial distribution of the condensate with respect to the exciting laser spot in order to identify the condensation regimes. Using tomography, we have measured the 2D spatial image of the polariton emission below and above threshold attemperatures ranging from 10K to 300K. We are able to study the diffusion and propagation of a polaritons depending on the exciton density as well as on the microcavity thickness gradient. Figure 1 presents the photoluminescence spectra and the spectrally resolved images, and evidences an asymetric polariton propagation above threshold. This is a first step towards the optical manipulation of macroscopic quantum fluids in ZnO at room temperature. The authors acknowledge financial support from FP7 program through ITN networks CLERMONT4 (235114). References [1] E. Wertz et al., Phys. Rev. Lett. 109, 216404 (2012) [2] F. Li et al., Phys. Rev. Lett. 110, 196406 (2013)

ZnO is a wide bandgap semiconductor with strong excitonic properties, in particular a large oscillator strength and a large exciton binding energy. It therefore raises a strong interest for the demonstration of polariton lasing up to room temperature with microcavities in the strong exciton-photon coupling regime. The strong coupling regime has recently been demonstrated for planar ZnO microcavities fabricated by various approaches. In this work, we report polariton condensation over a broad range of temperatures, up to room temperature, and of exciton-photon composition for the polariton condensate. This is the outcome of the improvement beyond Q=2000 of the microcavity quality factor, one of the key parameters for polariton condensation.Our fully-hybrid bulk ZnO microcavity combines a high quality active region, made up of bulk ZnO from a thinned substrate, and a cavity with a high quality factor, enabled by two dielectric mirrors. The large variation of the cavity thickness allows to analyze polariton condensation processes in thin () as well as thick (2 to 3 ) cavities. The Rabi splitting approaches 250 meV. Polariton condensation is obtained systematically [1], over a wide range of exciton-photon detuning and of temperature up to 300K. The complete phase diagram of the ZnO polariton laser is drawn (cf figure 1a), showing that its threshold is only 6 times larger at 300 K than at 8 K. It is in a good qualitative agreement with the simulations of exciton and polariton relaxation in a kinetic model (figure 1b). Strongly excitonic (96% exciton fraction) as well as strongly photonic condensates (83% photon fraction) are realized, that pave the way to promising advances of the polariton physics in ZnO microcavities. This tunability represents an important progress compared to our previous demonstration of a ZnO polariton laser in a Q=450 microcavity [2], as well as to other recent reports [3]. It also confers a strong advantage to ZnO microcavities compared to GaN [4], since thanks to their very large Rabi splitting the optimal detuning for condensation is positive, instead of negative, at moderate temperatures, and close to zero at room temperature. One important consequence is that more excitonic condensates (i.e. with stronger interactions, and therefore nonlinearities) can be generated and investigated.

The spatial distribution of photon modes confined in a 0D cavity and a 1D W1 waveguide is investigated on AlN-based photonic crystal (PC) membranes by spectrally resolved scanning confocal microscopy in the ultra-violet spectral range. The influence of the fabrication-induced disorder of the PC on the photon modes is analyzed. The cavity modes are shown to be robust with respect to disorder, whereas the 1D modes of the W1 waveguide are localized near its cut-off frequency. Those modifications of the lowest energy photonic modes are compared to simulations of weakly disordered photonic structures.

A ZnO planar optical microcavity displaying room-temperature polariton lasing has been fabricated. The cavity combines optimum crystalline quality, as given by the ZnO bulk single-crystal substrate employed as active region, and optimum photonic quality, as obtained by the use of two dielectric SiO2/HfO2 Bragg mirrors. A maximum cavity quality factor of about 3000 has been measured, enabling the observation of room-temperature polariton lasing in a wide range of cavity-exciton detuning conditions. Typically, the polariton lasing transition is accompanied by an increase of the output intensity by more than two orders of magnitude, a reduction of the emission linewidth by a factor 5 and a relatively small blueshift of the lower polariton branch (less than 5% of the Rabi splitting).

We report exciton-polariton condensation in a new family of fully hybrid ZnO based microcavity demonstrating the best-quality ZnO material available (a bulk substrate), a large quality factor (~4000) and large Rabi splittings (~240 meV). Condensation is achieved between 4 and 300 K and for excitonic fractions ranging between 17% and 96 %, which corresponds to a tuning of the exciton-polariton mass, lifetime and interaction constant by one order of magnitude. We demonstrate mode switching between polariton branches allowing, just by controlling the pumping power, to tune the photonic fraction by a factor 4.