Theory and data analysis for excitations in liquid $^4$He beyond the roton minimum

TL;DR

This paper revisits the excitation spectrum of liquid helium-4 beyond the roton minimum, incorporating interference effects to refine the dispersion relation and demonstrate the persistence of undamped excitations at high momentum.

Contribution

It introduces a model that includes interference effects between one and two excitations, improving the accuracy of the high-momentum dispersion relation for liquid helium-4.

Findings

Undamped excitations persist up to Q=3.6 Å^{-1} due to attractive roton interactions.

Refined dispersion relation extracted from experimental data.

Interference effects significantly impact excitation behavior beyond the roton minimum.

Abstract

The hybridization of the single-excitation branch with the two-excitation continuum in the momentum region beyond the roton minimum is reconsidered by including the effect of the interference term between one and two excitations. Fits to the latest experimental data with our model allow us to extract with improved accuracy the high momentum end of the $^4$He dispersion relation. In contrast with previous results we find that the undamped excitations below two times the roton energy survive up to Q=3.6 A^{-1} due to the attractive interaction between rotons.