Critcal velocity of superfluid flow past large obstacles in Bose-Einstein condensates

By considering the stability of potential how of a superfluid around large obstacles of size R, we derive an analytical result for the critical velocity that is of order v(c)similar to(h) over bar /mR, scaling inversely with obstacle size, in contrast to what is obtained from a Landau criterion. Our results are compared with nutnerical solutions of the aross-Pitaevskii equation and with recent measurements of the critical velocity in Bose-Einstein condensates of dilute atomic gases.