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arXiv:cond-mat/9607114 · Physical Review A

Stability of Bose condensed atomic Li7

M. Houbiers, Henk T. C. Stoof

Published Dec 1, 1996• 107 citations
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Abstract

We study the stability of a Bose condensate of atomic $^{7}\mathrm{Li}$ in a (harmonic oscillator) magnetic trap at nonzero 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. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.54.5055

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The strongly ferromagnetic spin-1 Bose-Einstein condensate has recently been realized with atomic Li7 . It was predicted that a strong ferromagnetic interaction can drive the normal gas into a magnetized phase at a temperature above the superfluid transition, and Li7 likely satisfies the criterion. We reexamine this theoretical proposal employing the two-particle-irreducible effective potential, and conclude that there exists no stable normal magnetized phase for a dilute ferromagnetic Bose gas. For Li7 , we predict that the normal gas undergoes a joint first-order transition and jumps directly into a state with finite condensate density and magnetization. We estimate the size of the first-order jump and examine how a partial spin polarization in the initial sample affects the first-order transition. We propose a qualitative phase diagram at fixed temperature for the trapped gas. Published by the American Physical Society 2024
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