Superradiant Decay of Cyclotron Resonance of Two-Dimensional Electron   Gases
  We report on the observation of collective radiative decay, or superradiance, of cyclotron resonance (CR) in high-mobility two-dimensional electron gases in GaAs quantum wells using time-domain terahertz magnetospectroscopy. The decay rate of coherent CR oscillations increases linearly with the electron density in a wide range, which is a hallmark of superradiant damping. Our fully quantum mechanical theory provides a universal formula for the decay rate, which reproduces our experimental data without any adjustable parameter. These results firmly establish the many-body nature of CR decoherence in this system, despite the fact that the CR frequency is immune to electron-electron interactions due to Kohn's theorem. 
Qi Zhang, Takashi Arikawa, Eiji Kato, John L. Reno, Wei Pan, John D.   Watson, Michael J. Manfra, Michael A. Zudov, Michail ...
cond-mat.mes-hall