Bose-Einstein Condensation, the Lambda Transition, and Superfluidity for Interacting Bosons

TL;DR

This paper models Bose-Einstein condensation and superfluidity in interacting bosons, revealing new phenomena and providing detailed simulations that align with experimental observations.

Contribution

It introduces a molecular-level description of the lambda transition in interacting bosons, identifying phenomena absent in ideal gas models, and connects simulation results with experimental data.

Findings

Diverging heat capacity near transition in Lennard-Jones helium-4 simulations

Continuous growth of ground state occupancy from pure permutation loops

Discontinuous transition with latent heat in mixed permutation loops

Abstract

Bose-Einstein condensation and the $\lambda$-transition are described in molecular detail for bosons interacting with a pair potential. New phenomena are identified that are absent in the usual ideal gas treatment. Monte Carlo simulations of Lennard-Jones helium-4 neglecting ground momentum state bosons give a diverging heat capacity approaching the transition. Pure permutation loops give continuous growth in the occupancy of the ground momentum state. Mixed ground and excited momentum state permutation loops give a discontinuous transition to the condensed phase. The consequent latent heat for the $\lambda$-transition is 3\% of the total energy. The predicted critical velocity for superfluid flow is within a factor of three of the measured values over three orders of magnitude in pore diameter.