Spontaneous nonground state polariton condensation in pillar microcavities

We observe spontaneously driven nonground state polariton condensation in GaAs pillar microcavities under nonresonant optical excitation. We identify a regime where the interplay of exciton-exciton and pair polariton scattering can lead to mode switching from nonground state to ground state polariton condensation. A simple kinematic model satisfactorily describes the observed mode switching as each of the above scattering mechanisms becomes prevalent at different carrier densities.

Figure 1

(Color online) (a) Reflectivity spectrum of the sample; the arrow indicates the energy of excitation. (b) Below threshold time and spectrally resolved photoluminescence from a $3.2\mu \text{m}$ side square pillar at 0 meV and (c) $-13\text{meV}$ detuning conditions. (d) Power dependence of the emission intensity and (e) the energy blueshift that occurs for a $3.2\mu \text{m}$ square pillar at 0 meV (green dots) and $-13\text{meV}$ (blue squares) detuning. The hollow blue squares correspond to the higher energy mode that exhibits polariton condensation for a certain range of excitation powers. (c), (f), and (g) Time and spectrally resolved photoluminescence from a $3.2\mu \text{m}$ pillar at $-13\text{meV}$ detuning below threshold, at threshold, and above threshold respectively (false color/grayscale images with blue/dark gray signifying higher intensity).

Figure 2

Below threshold photoluminescence spectrum from a $3.2\mu \text{m}$ square pillar at $\delta =-13\text{meV}$ detuning and schematic representation of the energy transitions between the exciton reservoir and polariton states M1, M2, and M5. Arrows indicate exciton-exciton and pair-polariton scattering between the states.

Figure 3

(Color online) Comparison of the measured photoluminescence decay curves (solid black lines) and the fit of the kinematic model (dashed red lines). Columns correspond to different polariton states (M1, M2, and M5 from left to right) and rows to different excitation power (below threshold, at threshold and above threshold from top to bottom).