Estimate of surfon evaporation time from the liquid helium surface due to the scattering on ripplons

Abstract

Recently a new type of surface excitations, surfons, has been proposed. Phenomenologically, these excitations can be interpreted as atoms on a surface quantum level. They explain the strong temperature dependence of surface tension coefficient of liquid helium. In the present work we studied theoretically the interaction of these excitations with ripplons, the quanta of surface waves. The lifetime of surfons due to the absorption of a ripplon and subsequent evaporation from the surface was estimated. The obtained surfon lifetime considerably exceeds the inverse surfon energy, substantiating the treatment of surfons as quasiparticles.

Neutrons on a surface of liquid helium

“…Recently, a new type of surface excitation was proposed [48] in addition to the ripplons, in order to explain the temperature dependence of the surface tension coefficient of liquid helium. These excitations, called surfons, are He atoms in a quasistationary discrete quantum energy level above the liquid helium surface [48][49][50]. The state is formed by the combination of the van-der-Waals attractive potential of the bulk helium and the hard-core repulsion between He atoms.…”

“…The perpendicular-to-surface surfon wave function Ψ ⊥ (z) was analyzed in Refs. [49][50][51] and shown to be localized above the surface on a height ∼ 0.4 nm ≪ z 0 [81]. Hence, for our calculation we may take Ψ 2 ⊥ (z) ≈ δ (z).…”

“…These excitations, called surfons, are He atoms in a quasistationary discrete quantum energy level above the liquid helium surface [48][49][50]. The state is formed by the combination of the van-der-Waals attractive potential of the bulk helium and the hard-core repulsion between He atoms.…”

Inelastic Neutron Scattering As an Indication of a New Type of Gapped Surface Excitations in Liquid He

“…The second process was studied in Ref. [32]. The evaporation rate 1/τ v of surfons depends on their initial momentum along the surface and grows rapidly with the increase of temperature.…”

“…The evaporation rate 1/τ v of surfons depends on their initial momentum along the surface and grows rapidly with the increase of temperature. [32] However, below 4K it does not exceed the limit ∼ E s / where the surfons cannot be called quasiparticles. The immersion rate of surfons to the liquid has not been calculated yet, but it should also be less than E s / , because in order to sink into the liquid, a He atom must overcome a potential barrier and rearrange the surrounding atoms of the liquid.…”