A new view on superfluidity

TL;DR

This paper develops a quantum statistical mechanics approach to superfluidity, explaining it as a thermodynamic equilibrium state with spontaneously broken symmetry due to stationary flow, and explores its properties and conditions.

Contribution

It extends the hierarchy of equations for reduced density matrices to include Bose-Einstein condensation, providing a new theoretical framework for understanding superfluidity.

Findings

Superfluidity corresponds to a thermodynamic equilibrium with broken symmetry.

The approach explains superfluidity as a stationary flow dependent on temperature.

Equations are solved in simplified cases illustrating the phenomenon.

Abstract

This paper represents the full version of a paper published earlier in Physica A [246 (1997), 275]. The present paper includes argumentation, proofs and details omitted in the shortened version. The papers are a further development of the approach in quantum statistical mechanics proposed by the author. The hierarchy of equations for reduced density matrices obtained previously is extended to the case corresponding to the Bose-Einstein condensation. The relevant state of the system with a condensate can be superfluid as well as nonsuperfluid. Special attention is given to the thermodynamics of superfluid systems. According to the results of the papers superfluidity is the state of a fluid whose symmetry is spontaneously broken because of a stationary flow. The state corresponds to thermodynamic equilibrium while the magnitude of the flow depends upon the temperature and is determined by thermodynamic considerations. The equations obtained are solved in two simple cases. The physical origin of superfluidity, peculiarities of the phenomenon in closed volumes and the critical velocity are discussed as well.