Stability of Bose condensed atomicLi7

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. © 1996 The American Physical Society.