Quantum theory of superfluidity and its onset in Bose films

A theory of superfluidity in two-dimensional Bose systems is presented. In contrast to the classical theory of Nelson and Kosterlitz, the excitation (rotons, ripplons, etc.) are treated quantum mechanically from the outset, resulting in an explicitly temperature-dependent vortex pair coupling proportional to the total mass density minus the normal mass density of the excitations. An application to thick ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films is presented, and the weakly interacting Bose system is discussed explicitly.