A combination of analytical and numerical approaches obtains the complete dispersion curve for surface excitations in a condensate held in a plane linear potential. This improvement on previous approximate results yields an accurate formula for the local Landau critical velocity for vortex formation at the surface of a sufficiently large condensate, which agrees very well with recent experiments.

• Received 28 June 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.240401