Lambda transition and Bose-Einstein condensation in liquid ${\rm ^4He}$

TL;DR

This paper develops a theory based on diatomic quasiparticles to explain the lambda transition and Bose-Einstein condensation in liquid helium-4, accurately predicting transition temperature and superfluid fractions.

Contribution

It introduces a novel diatomic quasiparticle approach to model BEC and superfluidity in liquid helium-4, aligning well with experimental and simulation data.

Findings

Lambda transition temperature predicted as 2.16 K, matching experimental 2.17 K.

Superfluid and BEC fractions agree with experimental data.

The theory provides a microscopic basis for BEC in liquid helium-4.

Abstract

We present a theory describing the lambda transition and the Bose-Einstein condensation (BEC) in a liquid ${\rm ^4He}$ based on the diatomic quasiparticle concept. It is shown that in liquid ${\rm ^4He}$ for the temperature region $1~{\rm K}\leq{\rm T}\leq {\rm T}_\lambda$ the diatomic quasiparticles macroscopically populate the ground state which leads to BEC in liquid ${\rm ^4He}$. The approach yields the lambda transition temperature as ${\rm T}_\lambda=2.16~{\rm K}$ which is in excellent agreement with the experimental lambda temperature ${\rm T}_\lambda=2.17~{\rm K}$. The concept of diatomic quasiparticles also leads to superfluid and BEC fractions which are in a good agreement with the experimental data and Monte Carlo simulations.