Recent advances in optical studies of condensed matter systems have led to the emergence of a variety of phenomena that have conventionally been studied in the realm of quantum optics. These studies have not only deepened our understanding of light-matter interactions but also introduced aspects of many-body correlations inherent in optical processes in condensed matter systems. This talk will describe our recent studies of cooperative spontaneous emission, or superradiance, predicted by Dicke in 1954, in two-dimensional (2D) semiconductors in a strong perpendicular magnetic field [1-4]. In one type of experiment, electron-hole pairs were incoherently prepared, but a macroscopic polarization spontaneously emerged and cooperatively decayed, emitting a giant pulse of coherent light, i.e., a superfluorescent burst [1-3]. In another type of experiment, we placed an ultrahigh-mobility 2D electron gas in a photonic-crystal cavity in a magnetic field and achieved strong light-matter coupling, which unraveld ultra-narrow (~10 GHz), true cyclotron resonance linewidths by suppressing superradiance. These results show that cooperative effects in solid-state systems are not just small corrections that require exotic conditions to be observed; rather, they dominate the nonequilibrium dynamics and light emission properties of interacting electrons.

1.       K. Cong, Physical Review B 91 , 235448 (2015).

2.       J.-H. Kim, Scientific Reports 3 , 3283 (2013).

3.       G. T. Noe II, Nature Physics 8 , 219 (2012).

4.       Q. Zhang, Physical Review Letters 113 , 047601 (2014).