lambda - type phase transition for a weakly interacting bose gas

It is suggested a general mechanism through which a lambda-type behavior is produced in the specific heat of a Bose gas near the critical temperature Tc . It is essential that the quasiparticle spectra have a gap proportional to the condensate. It works for a general class of quasiparticle spectra, and in particular, for the weakly interacting Bose gas. The introduction of a chemical potential in the theory is briefly discussed.