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Breaking the superfluid speed limit in a fermionic condensate

Research output: Contribution to Journal/MagazineLetterpeer-review

<mark>Journal publication date</mark>11/2016
<mark>Journal</mark>Nature Physics
Issue number11
Number of pages5
Pages (from-to)1017-1021
Publication StatusPublished
Early online date18/07/16
<mark>Original language</mark>English


Coherent condensates appear as emergent phenomena in many systems. They share the characteristic feature of an energy gap separating the lowest excitations from the condensate ground state. This implies that a scattering object, moving through the system with high enough velocity for the excitation spectrum in the scatterer frame to become gapless, can create excitations at no energy cost, initiating the breakdown of the condensate—the well-known Landau velocity. Whereas, for the neutral fermionic superfluid 3He-B in the T = 0 limit, flow around an oscillating body displays a very clear critical velocity for the onset of dissipation, here we show that for uniform linear motion there is no discontinuity whatsoever in the dissipation as the Landau critical velocity is passed and exceeded. Given the importance of the Landau velocity for our understanding of superfluidity, this result is unexpected, with implications for dissipative effects of moving objects in all coherent condensate systems.