Quartetting in fermionic matter and αα-particle condensation in nuclear systems

The onset of quartetting, i.e. αα-particle condensation, in symmetric nuclear matter is studied with the help of an in-medium modified four nucleon equation. It is found that at very low density, quartetting wins over pairing because of the strong binding of the αα particles. The critical temperature can reach values up to around 6 MeV. Also, the disappearance of αα particles with increasing density, i.e. the Mott transition, is investigated. In finite nuclei the Hoyle state, that is, the 02+ of 12C is identified as an ‘αα-particle condensate’ state. It is conjectured that such states also exist in heavier nαnα nuclei, such as 16O, 20Ne, etc. Exploratory calculations are performed for the density dependence of the αα-condensate fraction at zero temperature to address the suppression of the four-particle condensate below nuclear-matter density. Possible quartet condensation in other systems is discussed briefly.