Figure 4: Time-resolved THz response of condensed polaritons.
From: Revealing the dark side of a bright exciton–polariton condensate
Real part of the pump-induced THz conductivity Δσ1 (a) as a function of delay time τ, for ρ=ρ2, and (b) as a function of excitation density ρ, for τ=50 ps. The dielectric function Δε1 corresponding to both situations is shown in Supplementary Fig. 6. Blue spheres: experiment; black broken curves: two-component model fitting simultaneously Δσ1 and Δε1. Corresponding densities ρX and ρe–h extracted from the fits to a are displayed in e. Red shadows: a Lorentz function (full-width at half-maximum=3 meV) traces the departures between the experimental data and the two-component model due to polariton population at k||=0. GaP emitter and detector crystals are used in the experimental setup to resolve the THz signal between 8 and 22 meV. (c) Density ρcond of polaritons at k||=0 as a function of excitation density, as obtained by spectrally integrating the red shaded areas in b. Broken line: guide to the eye. (d) Densities of free carriers, ρe–h (green spheres), and reservoir excitons, ρX (blue spheres), as extracted by fitting the two-component model to the data in Fig. 3, displayed as a function of τ. The excitation density is ρ=ρ1. The data are compared with the time-resolved PL intensity (black curve) obtained from streak camera measurements (Supplementary Fig. 10). (e) Corresponding data obtained above the critical excitation density ρ=ρ2. ρe–h (green spheres), ρX (blue spheres) and ρcond (red spheres) are extracted from a.
