Abstract
The problem of liquid helium is treated in terms of the theory of collective coordinates, applying a canonical transformation similar to that used previously for plasmas. This treatment provides further physical and mathematical insights into the origin of phonons, and into the nature of the roton excitations and their interactions. In particular, starting from the many-body Hamiltonian, it directly gives the Feynman-Cohen wave function, and the dipole-dipole interaction of rotons, along with certain further predictions with regard to the roton spectrum and the correlation function. The property of superfluidity is explained by the subsidiary conditions which imply that individual particle excitations are impossible in the lowlying states of the system. The transformed Hamiltonian can thus be shown to have eigenfunctions corresponding to quantized vortices.
DOI:https://doi.org/10.1103/RevModPhys.39.894
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