Multi-Branch Structure of the Excitation Spectra in Liquid Helium II

Abstract

The multi-branch structure of the excitation spectra in liquid helium II is clarified on the basis of the formulae from which the phonon-roton spectrum has been successfully derived in previous papers. The existence of the flat spectrum and the broad free-atom spectrum revealed by Cowley and Woods is confirmed theoretically. The new excitation spectrum with energy 40 °K at momentum 1.13Å-1 which has recently been found by Woods, Svensson and Martel is derived and an excellent agreement with experiment is obtained.