Eur. Phys. J. D (2014) 68: 191
https://doi.org/10.1140/epjd.e2014-40535-7

Regular Article

A dense Bose fluid at zero temperature: condensation and clusters in liquid ⁴He

Physics Department, The University of Auckland, Private Bag, 92019 Auckland, New Zealand

^a e-mail: v.kruglov@auckland.ac.nz

Received: 29 August 2013
Received in final form: 4 December 2013
Published online: 24 July 2014

Abstract

We present a full set of wave equations describing a dense Bose fluid, applicable both to non-ideal gases and to liquid ⁴He. The phonon spectrum in liquid ⁴He is found and the fraction of condensed particles is calculated at zero temperature for a wide range of densities. The theory also yields the ground-state energy for the quantum liquid ⁴He in agreement to high accuracy with Monte Carlo simulations and experimental data at low pressure. A new and essential point is the the introduction of a momentum space cutoff at the speed of the second sound. We also present the derivation of a generalized Hartree-Fock equation describing roton clusters in low temperature liquid ⁴He, allowing us to confirm that, at low enough temperatures and for a wide range of pressures, the stable clusters consist of 13 bound atoms.