Beyond the Landau Criterion for Superfluidity
Sara Ianeselli, Chiara Menotti, Augusto Smerzi
Abstract
According to the Landau criterion for superfluidity, a Bose-Einstein condensate flowing with a group velocity smaller than the sound velocity is energetically stable to the presence of perturbing potentials. We found that this is strictly correct only for vanishingly small perturbations. The superfluid critical velocity strongly depends on the strength and shape of the defect. We quantitatively study, both numerically and with an approximate analytical model, the dynamical response of a one-dimensional condensate flowing against an istantaneously raised spatially periodic defect. We found that the critical velocity vc decreases by incresing the strength of the defect V0, up to to a critical value of the defect intensity where the critical velocity vanishes.
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