Enhancement of microcavity polariton relaxation under confinement

Abstract

We experimentally investigate the relaxation of spatially confined microcavity polaritons. We measure the time-and energy-resolved photoluminescence under resonant excitation and in the low-density regime. In this way, we have access to the time evolution of the energy distribution of the polariton population. We show that, when one confined level is resonantly excited, after an initial transient, the population of the confined levels is thermally distributed. The reported efficiency of the relaxation process strongly depends on the confinement size. These experimental findings are well reproduced by a theoretical model accounting for the coupling between the confined states and a bath of acoustic phonons. Our results thus suggest that the phonon-mediated relaxation mechanisms are enhanced in the presence of spatial confinement.

Probability density tomography of microcavity polaritons confined in cylindrical traps of various sizes

“…Ref. [7] shows as well that relaxation mechanisms and thermalisation are enhanced as the trap size decreases.…”

“…The diameter of the excitation spot is 30 µm. This hot excitation creates electron hole pairs which relax to the confined and delocalized polariton states [7,8]. Then, due to the coupling with extra-cavity photons, the eigenmodes emit photoluminescence (PL), which is collected with a 0.5 NA microscope objective and imaged on the slit of a spectrometer using a lens with 25 cm focal length, with a diffraction limited spatial resolution.…”

“…1(a)-(c) are due to the different photonic fraction of the confined states [10] and to thermalisation towards the lower energy states [7]. Ref.…”

“…The temperature of the system can be extracted from the PL data as described in Ref. [7]. It varies according to the excitation conditions and to the detuning of the photonic modes with respect to the excitonic resonance.…”

Polariton lasing in high-quality selenide-based micropillars in the strong coupling regime

“…It was pointed out already that confinement is enhancing polariton relaxation by phonons. 31 However, in the polariton lasing regime, it is unlikely the dominant mechanism of stimulated relaxation, rather driven as discussed above by two-body scattering. Another mechanism, better known in the context of polariton lasing in planar microcavities, is more likely; unlike for regular lasers, the gain medium is always transparent for polaritons even in the nonexcited regions.…”