title: Dynamical instability of a condensate induced by a rotating thermal gas.
abstract: We study surface modes of the condensate in the presence of a rotating thermal cloud in an axisymmetric trap. By considering collisions that transfer atoms between the condensate and the noncondensate, we find that m>0 modes, which rotate in the same sense as the thermal cloud, damp less strongly than m<0 modes, where m is the polarity of the excitation. We show that above a critical angular rotation frequency, equivalent to the Landau stability criterion, m>0 modes become dynamically unstable, leading to the possibility of vortex nucleation. We also generalize our stability analysis to treat the case where the stationary state of the condensate already possesses a single vortex.
authors.affiliation: Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7.
authors.forename: J E
authors.initials: JE
authors.lastname: Williams
authors.forename: E
authors.initials: E
authors.lastname: Zaremba
authors.forename: B
authors.initials: B
authors.lastname: Jackson
authors.forename: T
authors.initials: T
authors.lastname: Nikuni
authors.forename: A
authors.initials: A
authors.lastname: Griffin