Interactions in Confined Polariton Condensates

We investigate the effect of interactions in zero-dimensional polariton condensates. The shape of the condensate wave function is shown to be modified by repulsive interactions with the reservoir of uncondensed excitons. In large micropillar cavities, when uncondensed excitons are located at the center, the condensate is ejected toward the pillar edges. The same effect results in the generation of optical traps in wire cavities. Once polariton condensates are spatially separated from the excitonic reservoir, spectral signatures of polariton-polariton interactions within the condensate are evidenced.

Figure 1

(a) Top: Scanning electron microscopy image of a micropillar. The dashed circle and blue line schematically indicate the spatial location of the excitonic reservoir and of confined polaritons; bottom: spatially and spectrally resolved emission of a single $5\mu \mathrm{m}$ micropillar measured below threshold. (b) Emission spectra measured on a $10\mu \mathrm{m}$ square pillar for several excitation powers. (c)–(e) Spatial distribution of the total emission intensity measured on the same $10\mu \mathrm{m}$ pillar for three excitation powers. (f)–(h) Corresponding calculated intensity distributions of the lowest energy polariton state. White dashed squares show the pillar edge.

Figure 2

(a) Spatially and spectrally resolved emission of a microwire excited $15\mu \mathrm{m}$ from its end for $P=3P_{\mathrm{th}}$. White lines: Calculated polariton states confined by the potential shown in white dashed line which includes interaction with the excitonic reservoir. Inset: Scanning electron micrography of the microwire with schematic representation of excitonic reservoir in dashed blue. (b) Same as (a) for $P=30P_{\mathrm{th}}$. The potential in white (red) dashed line also includes (does not include) the potential induced by the polarization occupancy. (c) Integrated intensity and spectral linewidth of the lowest energy polariton state measured in the optical trap as a function of excitation power.

Figure 3

(a) Blueshift measured in a 10, 6, and $3.2\mu \mathrm{m}$ micropillar and in the optical trap. The dashed red (solid blue) line shows the excitation range dominated by interactions with the reservoir (within the condensate). The inset shows the measured intensity in the four systems. (b) Symbols: Measured blueshift of the lowest energy polariton state in the $10\mu \mathrm{m}$ micropillar. Calculated blueshift induced (dashed red line) by the excitonic reservoir or (solid blue line) by interactions within the condensate deduced from the measured polariton occupancy, (black line) total calculated blueshift. (c) Same as (b) for the optical trap.

Figure 4

Emission spectrum measured in a $10\mu \mathrm{m}$ square micropillar at $30P_{\mathrm{th}}$ in the photon lasing regime. The corresponding spatial emission pattern is shown in the inset where the white dashed square shows the pillar edge.