Stability of Bose condensed atomic Li-7

TL;DR

This paper investigates the stability of a Bose-Einstein condensate of lithium-7 atoms in a magnetic trap at finite temperatures, proposing a stability criterion based on free energy extremum and analyzing how temperature affects condensate stability.

Contribution

It introduces a stability criterion for Bose condensates inspired by neutron star physics and examines temperature effects on condensate stability and particle number at the instability point.

Findings

Condensate stability is linked to free energy extremum with conserved particle number.

The number of condensate particles at instability decreases as temperature increases.

Normal gas component remains stable against density fluctuations at the instability point.

Abstract

We study the stability of a Bose condensate of atomic $^7$Li in a (harmonic oscillator) magnetic trap at non-zero temperatures. In analogy to the stability criterion for a neutron star, we conjecture that the gas becomes unstable if the free energy as a function of the central density of the cloud has a local extremum which conserves the number of particles. Moreover, we show that the number of condensate particles at the point of instability decreases with increasing temperature, and that for the temperature interval considered, the normal part of the gas is stable against density fluctuations at this point.