Fermi-edge superfluorescence from a quantum-degenerate electron-hole gas

Abstract

Nonequilibrium can be a source of order. This rather counterintuitive statement has been proven to be true through 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 appearance of macroscopic coherence. Here, we report on the observation of spontaneous bursts of coherent radiation from 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 observed emission occurs at the quasi-Fermi edge of the carrier distribution. As the carriers are consumed by recombination, the quasi-Fermi energy goes down toward the band edge, and we observe a continuously red-shifting streak. We interpret this emission as cooperative spontaneous recombination of electron-hole pairs, or superfluorescence (SF), which is enhanced by Coulomb interactions near the Fermi edge. This novel many-body enhancement allows the magnitude of the spontaneously developed macroscopic polarization to exceed the maximum value for ordinary SF, making electron-hole SF even more “super” than atomic SF.

Dicke superradiance in solids [Invited]

“…Excitonic interactions and coupling between electrons and holes are particularly important both in superradiant decays and superfluorescent bursts [56]. Massively Fermi-degenerate electrons and holes, which would never occur in atomic-like systems, can lead to many-body enhancement of gain, which induces preferential production of a superfluorescent burst at the Fermi edge [140]. This is still a rapidly progressing field of research, expanding to encompass more and more nontraditional physical situations for SR and SF, such as plasmon excitations [43,61] and exciton-plasmon coupling [170,171], with unique solid-state cavities to create nonintuitive many-body playgrounds [60,169,172].…”

“…12. Two fibers, center and edge fibers, were used for PL collection; the former was used for monitoring spontaneous emission (which was emitted in all 4π spatial directions with equal probability), while the latter was used to observe SF (which was emitted in the plane of the QWs) [56,140,141,143]. TIPL was measured with a CCD-equipped monochromator, and TRPL was measured either using a streak camera system or a Kerrgate method.…”

“…Figures 19(a)-19(e) show SF emission as a function of photon energy and time delay at various B [140]. With increasing B, the number of peaks decreases, and the energy separation between LLs increases due to increasing Landau quantization.…”

Superfluorescence from photoexcited semiconductor quantum wells: Magnetic field, temperature, and excitation power dependence

“…Two fibers, center and edge fibers, were used for PL collection; the former was used for monitoring SE (which is emitted in all 4π spatial directions with equal probability) while the latter was used to observe SF (which is emitted in the plane of the quantum wells). 19,20,22 In the SF regime, the emission is strongly directional, propagating along a certain in-plane direction, but the direction changes from shot to shot.…”

“…19 Many-body renormalization of energies was noted, 20 and Coulomb enhancement of gain at the Fermi edge 21 was found to assist cooperative recombination, leading to a novel phenomenon of sequential SF bursts. 22 Overall, it has been established that Coulomb interactions among carriers and continuum of states, unique to solid states systems, distinguish solid-state SF from atomic SF. However, quantitative understanding of the observability conditions for SF has not been accomplished.…”