Effects of temperature upon the collapse of a Bose-Einstein condensate in a gas with attractive interactions

We present a study of the effects of temperature upon the excitation freque ncies of a Bose-Einstein condensate formed within a dilute gas with a weak attractive, effective interaction between the atoms. We use the self-consis tent Hartree-Fock Bogoliubov treatment within the Popov approximation, and we compare our results to previous zero-temperature and Hartree-Fock calcul ations. The metastability of the condensate is monitored by means of the l = 0 excitation frequency. As the number of atoms in the condensate is incre ased, with T held constant, this frequency goes to zero, signalling a phase transition to a dense collapsed state. The critical number for collapse is found to decrease as a function of temperature, the rate of decrease being greater than that obtained in previous Hartree-Fock calculations.