Condensation dynamics in a two-dimensional square photonic crystal waveguide

Exciton-polariton condensation occurs at the dispersion extrema, where the density of states diverges and polaritons can naturally accumulate. The existence of multiple such points leads to coupling and competition between the associated modes and dynamical redistribution of the polaritons in the dispersion. Here, we directly engineer the above situation via subwavelength periodic patterning of a two-dimensional nanostructure. This leads to multiple condensates that form at high-momenta, accidental-coupling points, and a high-symmetry Γ point with a bound-in-the-continuum state. The dynamical behavior of the system reveals the nonsimultaneous appearance of these condensates and the interplay of gain and relaxation mechanisms. We fully characterize the quasistatic and dynamical regime of this artificial crystal and the properties of the different condensates. This understanding is necessary when band-structure engineering techniques are used to achieve precise control of condensate formation with given energy and momentum.