Momentum distribution of liquid 4He across the normal-superfluid phase transition

TL;DR

This study uses path integral Monte Carlo simulations to analyze how the momentum distribution and elementary excitations of liquid helium-4 change across the normal-superfluid phase transition, revealing a kink associated with roton excitations that vanishes in the normal phase.

Contribution

First simulation-based investigation of momentum distribution changes across the superfluid transition in liquid helium-4, highlighting unexplained phenomena.

Findings

Presence of a kink in momentum distribution in the superfluid phase

Disappearance of the kink in the normal phase

Unexplained behavior of the transition in current theories

Abstract

We have carried out a study of the momentum distribution and of the spectrum of elementary excitations of liquid $^4$He across the normal-superfluid transition temperature, using the path integral Monte Carlo method. Our results for the momentum distribution in the superfluid regime show that a kink is present in the range of momenta corresponding to the roton excitation. This effect disappears when crossing the transition temperature to the normal fluid, in a behavior currently unexplained by theory.