The authors have studied the question of whether pairs of neutrons and pairs of protons of the usual superfluid phases form a bound state to give rise to a superfluid condensate of "$\alpha$ particles." They indeed find indications for this to be the case from a BCS-like study for bosons using the proton-neutron interacting-boson model as well as from an even-odd effect in the number of pairs using experimental binding energies.

• Received 11 July 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.1235