Cooperative coherent phenomena in annihilating electron-positron and electron-hole plasmas in a strong magnetic field

Until now, the phenomenon of collective spontaneous emission (superradiance) was studied, as a rule, for the atomic systems with a discrete energy spectrum. However, it acquires essentially new features in the systems with continuous energy spectra of particles. Two examples of such systems are an electron-position plasma and an electron-hole semiconductor plasma. The review is devoted to the analysis of cooperative, coherent phenomena in these media which demonstrate new remarkable effects of fundamental importance for quantum electrodynamics. The possibility of collective spontaneous annihilation of an electron-positron plasma in a strong magnetic field is predicted. Collective annihilation develops considerably more rapidly than the known incoherent processes of spontaneous annihilation and collisional relaxation and leads to the generation of powerful coherent γ-radiation (annihilation superradiance). The nonrelativistic analog of the electron-positron annihilation is the process of interband recombination of quasiparticles (electrons and holes) in direct-gap bulk semiconductors. We establish the feasibility of collective recombination (recombination superradiance) of a magnetized electron-hole plasma, which develops through interband recombination of free electrons and holes in direct band-gap semiconductors. The limiting parameters of the ultrashort pulses of the recombination superradiance are found. According to our estimates for GaAs, in the magnetic fields of the order of (105 – 106) G the coherent optical pulses of duration (0.1 – 1) ps and intensity 100 MW/cm2 can be generated spontaneously in the samples of typical sizes 3 μm2 × 30 μm and electron-hole density 5 × 1017 cm−3.