Critical Trap Aspect Ratios For Dipolar BEC

We show that there exists critical trap aspect ratios for a trapped Bose-Einstein condensate with dipole-dipole interactions. We discuss the role of critical trap aspect ratios on both the critical angular velocity above which a vortex is energetically favorable and the precession velocity of an off-axis vortex in TF regime. We show that the stability diagram for a purely dipolar gas depends crucially on the critical trap aspect ratios both for positive and negative strength of dipolar interaction. We prove that the critical points can be changed by an anharmonic potential.