SUPERFLUIDITY IN THE NEW QUANTUM-STATISTICAL APPROACH

This paper is a further development of the approach in quantum statist ical mechanics proposed by the author. The hierarchy of equations for reduced density matrices obtained previously is extended to the case c orresponding to the Bose condensation. The relevant state of the syste m with a condensate can be superfluid as well as nonsuperfluid. Specia l attention is given to the thermodynamics of superfluid systems. Acco rding to the results of the paper superfluidity is the state of a flui d whose symmetry is spontaneously broken because of a stationary flow. The state corresponds to thermodynamic equilibrium while the magnitud e of the flow depends upon the temperature and is determined by thermo dynamic considerations. The physical origin of superfluidity, peculiar ities of the phenomenon in closed volumes and the critical velocity ar e discussed as well.