Dynamical conductivity of the GaAs two-dimensional electron gas at low temperature and carrier density

We use infrared cyclotron-resonance measurements to study the dynamical conductivity of a gated GaAs two-dimensional electron gas in a perpendicular magnetic field in the regime of low carrier density and temperature where electron correlation and exchange effects are most important. For T0.4 K the resonance narrows and shifts dramatically as the density is reduced below the point at which the lowest spin-split Landau level is filled. This observation provides the first demonstration of a strong influence of electron-electron interactions on the cyclotron-resonance line shape. © 1986 The American Physical Society.