Dynamic many-body theory: Dynamic structure factor of two-dimensional liquid $^4$He

TL;DR

This paper presents a detailed theoretical calculation of the dynamic structure factor of two-dimensional liquid helium-4 at zero temperature, revealing phonon-maxon-roton features and a second roton-like excitation near the phase transition.

Contribution

It introduces a multi-particle fluctuations approach up to infinite order to accurately model the dynamic structure factor in 2D liquid helium-4.

Findings

Qualitative similarity to 3D phonon-maxon-roton curve

Identification of a Pitaevskii plateau in 2D

Emergence of a second roton-like excitation near phase transition

Abstract

We calculate the dynamic structure function of two-dimensional liquid $^4$He at zero temperature employing a quantitative multi-particle fluctuations approach up to infinite order. We observe a behavior that is qualitatively similar to the phonon-maxon-roton-curve in 3D, including a Pitaevskii plateau (L. P. Pitaevskii, Sov. Phys. JETP 9, 830 (1959)). Slightly below the liquid-solid phase transition, a second weak roton-like excitation evolves below the plateau.