Abstract
Preparation and characterization of polariton Bose–Einstein condensates in micro-cavities of high quality are at the frontier of contemporary solid state physics. Here, we report on three-dimensional polariton condensation and confinement in pseudo-spherical ZnO microcrystals. The boundary of micro-spherical ZnO resembles a stable cavity that enables sufficient coupling of radiation with material response. Exciting under tight focusing at the low frequency side of the bandgap, we detect efficiency and spectral nonlinear dependencies, as well as signatures of spatial delocalization of the excited states which are characteristics of dynamics in polariton droplets. Expansion of the photon component of the condensate boosts the leaky field beyond the boundary of the ZnO microcrystals. Using this, we observe surface polariton field enhanced Raman responses at the interface of ZnO microspheres. The results demonstrate how readily available spherical semiconductor microstructures facilitate engineering of polariton based electronic states and sensing elements for diagnostics at interfaces.
Highlights
Preparation and characterization of polariton Bose–Einstein condensates in micro-cavities of high quality are at the frontier of contemporary solid state physics
We explore the potential for polariton Bose–Einstein condensation (BEC) in two readily available representative Zinc oxide (ZnO) microstructures of pseudo-spherical geometry, which provide conditions that resemble a stable cavity[18,19]
The spectra of the two systems demonstrate inhomogeneous broadening at the red side of the edge emission. This is the spectral region where longitudinal optical phonons dominate in the emission response from ZnO bulk[9]
Summary
Preparation and characterization of polariton Bose–Einstein condensates in micro-cavities of high quality are at the frontier of contemporary solid state physics. We report on threedimensional polariton condensation and confinement in pseudo-spherical ZnO microcrystals. The discovery of Bose–Einstein condensation (BEC) of polaritons has been reported in micro-cavities of high quality8— the discovery of which has yet to find practical application. Within this context, the properties of Zinc oxide (ZnO) are interesting: ZnO has an ultraviolet band gap (∼3.37 eV), a large exciton binding energy (∼60 meV), and a large oscillator strength[9]. We explore the potential for polariton BEC in two readily available representative ZnO microstructures of pseudo-spherical geometry, which provide conditions that resemble a stable cavity[18,19]. The first is ZnO analytical standard microcrystals (size ca. 100 μm) from Sigma-Aldrich, and the second are unannealed ZnO polycrystalline microspheres (particle size ca. 2 μm) that can be readily synthesized[20]: please, refer to
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