Roton Bound States in Liquid 4He
The low lying excited states of liquid 4He are long lived “quasiparticle” excitations which are described by the familiar phonon-roton dispersion curve.1 Since the liquid is isotropic, the quasiparticle density of states is singular at the energy of the roton minimum ΔR (and also at the energy of the maximum in the dispersion curve). Scattering processes in which quasiparticles decay into roton pairs are enhanced by the singular density of states, leading to a splitting of the dispersion curve into two branches.2,3,4 The roton pair scattering amplitude is similarly enhanced, and an arbitrarily small attractive roton interaction is sufficient to form roton bound states.3
KeywordsHelium Propa Dition Fargo
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