Interacting Rotons and Superfluidity in Liquid Helium

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Abstract
A theory based on roton-roton interaction is developed for the superfluid phase transition in liquid helium. The roton coupling causes a decrease of the roton energy with increasing temperature; thus the roton exhibits a soft-mode behavior, in common with other second-order phase transitions. The calculated superfluid density is in remarkable agreement with experiment, and the roton softening is consistent with recent neutron data.