A Ginzburg-Landau model in superfluidity

A dynamical model for the normal-superfluid transition in 4He, accounting for variations of temperature and pressure, is proposed. The phenomenon is analyzed in the framework of Ginzburg-Landau theory characterizing the phase of the material with an order parameter related to the concentration of the superfluid particles. The constitutive choices allow one to prove the existence of a critical velocity above which superfluid properties disappear and to recover the usual phase diagram of liquid helium. The thermodynamic restrictions in the constitutive relations which ensure the Clausius-Duhem inequality have been pointed out.