Figure 4. Interpretation of the burst of emission with dynamically red-shifting wavelength: coherent Fermi-edge emission via ultrafast superradiant recombination of an electron-hole plasma.

(a), Zero magnetic field. Carriers near the instantaneous quasi-Fermi energies are consumed through ultrafast cooperative recombination, due to many-body enhancement of gain²¹, leading to both a burst of radiation with continuously red-shifting wavelength and a continuously decreasing Fermi energy towards the band edge. (b), Finite magnetic field. Electron-hole pairs at the highest occupied Landau levels recombine first, again due to many-body enhancement of gain, leading to sequential bursts of superfluorescece from higher to lower Landau levels toward the (00) level.