Condensate and superfluid fraction of homogeneous Bose gases in a self-consistent Popov approximation

TL;DR

This paper investigates the behavior of condensate and superfluid fractions in homogeneous Bose gases using a self-consistent Popov approximation, revealing a novel non-monotonic condensate fraction at finite temperatures that can be tested experimentally.

Contribution

It introduces a detailed analysis of condensate and superfluid fractions with a focus on the non-monotonic condensate behavior, providing explicit expressions and experimental relevance.

Findings

Condensate fraction shows non-monotonic behavior with interaction strength at finite temperature.

Superfluid fraction behaves differently from condensate fraction.

Finite size effects are analyzed within a semiclassical approximation.

Abstract

We study the condensate and superfluid fraction of a homogeneous gas of weakly interacting bosons in three spatial dimensions by adopting a self-consistent Popov approximation, comparing this approach with other theoretical schemes. Differently from the superfluid fraction, we find that at finite temperature the condensate fraction is a non-monotonic function of the interaction strength, presenting a global maximum at a characteristic value of the gas parameter, which grows as the temperature increases. This non-monotonic behavior has not yet been observed, but could be tested with the available experimental setups of ultracold bosonic atoms confined in a box potential. We clearly identify the region of parameter space that is of experimental interest to look for this behavior and provide explicit expressions for the relevant observables. Finite size effects are also discussed within a semiclassical approximation.