Nonequilibrium can be a source of order. This rather counterintuitive statement has been proven to be truethrough a variety of fluctuation-driven, self-organization behaviors exhibited by out-of-equilibrium,many-body systems in nature (physical, chemical, and biological), resulting in the spontaneous appearanceof macroscopic coherence. Here, we report on the observation of spontaneous bursts of coherent radiationfrom a quantum-degenerate gas of nonequilibrium electron-hole pairs in semiconductor quantum wells.Unlike typical spontaneous emission from semiconductors, which occurs at the band edge, the observedemission occurs at the quasi-Fermi edge of the carrier distribution. As the carriers are consumed byrecombination, the quasi-Fermi energy goes down toward the band edge, and we observe a continuouslyred-shifting streak. We interpret this emission as cooperative spontaneous recombination of electron-holepairs, or superfluorescence (SF), which is enhanced by Coulomb interactions near the Fermi edge. Thisnovel many-body enhancement allows the magnitude of the spontaneously developed macroscopicpolarization to exceed the maximum value for ordinary SF, making electron-hole SF even more ﾑﾑsuperﾒﾒ thanatomic SF.
展开▼
