The Landau critical velocity for a particle in a Fermi superfluid

Abstract

We determine {à} la Landau the critical velocity $v\_c^L$ of a moving impurity in a Fermi superfluid, that is by restricting to the minimal excitation processes of the superfluid. $v\_c^L$ is then the minimal velocity at which these processes are energetically allowed. The Fermi superfluid actually exhibits two excitation branches~: one is the fermionic pair-breaking excitation, as predicted by BCS theory; the other one is bosonic and sets pairs into motion, as predicted by Anderson's RPA. $v\_c^L$ is the smallest of the two corresponding critical velocities $v\_{c,f}^L$ and $v\_{c,b}^L$. In the parameter space (superfluid interaction strength, fermion-to-impurity mass ratio), we identify two transition lines, corresponding to a discontinuity of the first-order and second-order derivatives of $v\_c^L$. These two lines meet in a triple point and split the plane in three domains. We briefly extend this analysis to the very recently realized case at ENS, where the moving object in the Fermi superfluid is a weakly interacting Bose superfluid of impurities, rather than a single impurity. For a Bose chemical potential much smaller than the Fermi energy, the topology of the transition lines is unaffected; a key result is that the domain $v\_c^L=c$, where $c$ is the sound velocity in the Fermi superfluid, is turned into a domain $v\_c^L=c+c\_B$, where $c\_B$ is the sound velocity in the Bose superfluid, with slightly shifted boundaries.

arXiv commentfinal version, both in english and in french

References in corpus (16)

• Theory of ultracold Fermi gases
• Condensation of Pairs of Fermionic Atoms Near a Feshbach Resonance
• Vortices and Superfluidity in a Strongly Interacting Fermi Gas
• Revealing the Superfluid Lambda Transition in the Universal Thermodynamics of a Unitary Fermi Gas
• Exploring the Thermodynamics of a Universal Fermi Gas
• The Unitary Fermi Gas: From Monte Carlo to Density Functionals
• Pure Gas of Optically Trapped Molecules Created from Fermionic Atoms
• Motion of a heavy impurity through a Bose-Einstein condensate
• A Mixture of Bose and Fermi Superfluids
• Precision Measurements of Collective Oscillations in the BEC-BCS Crossover
• Suppression and enhancement of impurity scattering in a Bose-Einstein condensate
• Collective mode of homogeneous superfluid Fermi gases in the BEC-BCS crossover
• Critical velocity for superfluid flow across the BEC-BCS crossover
• Dynamic structure factor of a superfluid Fermi gas
• Atom interferometric detection of the pairing order parameter in a Fermi gas
• Superfluidity of the 1D Bose gas

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