Giant superfluorescent bursts from a semiconductor magneto-plasma

Superradiance-the cooperative decay of excited dipoles-has recently been discussed in a diverse range of contexts in which coherent coupling of constituent particles governs their cooperative dynamics: cavity quantum electrodynamics, quantum phase transitions and plasmonics. Here we observe intense, delayed bursts of coherent radiation from a photo-excited semiconductor and interpret it as superfluorescence, where macroscopic coherence spontaneously appears from initially incoherent electron-hole pairs. The coherence then decays superradiantly, with a concomitant abrupt decrease in population from full inversion to zero. This is the first observation of superfluorescence in a dense semiconductor plasma, where decoherence is much faster than radiative decay, a situation never encountered in atomic cases. Nonetheless, a many-body cooperative state of phased electron-hole 'dipoles' does emerge at high magnetic fields and low temperatures, producing giant superfluorescent pulses. The solid-state realization of superfluorescence resulted in unprecedented controllability, promising tunable sources of coherent pulses.