Collective QED processes of electron-hole recombination and electron-positron annihilation in a strong magnetic field

The process of coherent spontaneous emission, originated from very fast collective recombination (annihilation) of electron-hole or electron-positron plasmas, is analysed. Such non-equilibrium systems of free particles and antiparticles with continuous energy spectra demonstrate cooperative features of fundamental importance for quantum electrodynamics. In particular, due to the self-consistent radiative coupling between active particles, a dense enough plasma bunch can emit an extremely short and powerful electromagnetic pulse. The phenomenon of recombination (annihilation) superradiance is expected to be very different from both usual lasing and well known Dicke superradiance in the atomic systems with discrete energy spectra. In the case of semiconductor magneto-optics, it is shown that subpicosecond, subgigawatt coherent pulses of recombination superradiance can be generated spontaneously in bulk GaAs samples placed in a strong (quantizing) magnetic field.