4-PARTICLE CONDENSATE IN STRONGLY COUPLED FERMION SYSTEMS

Four-particle correlations in fermion systems at finite temperatures a re investigated with special attention to the formation of a condensat e. Instead of the instability of the normal state with respect to the onset of pairing described by the Gorkov equation, a new equation is o btained which describes the onset of ''quartetting.'' Applying to symm etric nuclear matter, below a critical density, the four-particle cond ensation (alpha-like quartetting) is found to be favored over deuteron condensation (tripler pairing). This pairing-quartetting competition is expected to be a general feature of interacting fermion systems, su ch as the exciton-biexciton system in excited semiconductors. Possible experimental consequences are pointed out.