Instability of superfluid Fermi gases induced by a roton-like density mode in optical lattices

Abstract

We study the stability of superfluid Fermi gases in deep optical lattices in the BCS--Bose-Einstein condensation (BEC) crossover at zero temperature. Within the tight-binding attractive Hubbard model, we calculate the spectrum of the low-energy Anderson-Bogoliubov (AB) mode as well as the single-particle excitations in the presence of superfluid flow in order to determine the critical velocities. To obtain the spectrum of the AB mode, we calculate the density response function in the generalized random-phase approximation applying the Green's function formalism developed by Côté and Griffin to the Hubbard model. We find that the spectrum of the AB mode is separated from the particle-hole continuum having the characteristic rotonlike minimum at short wavelength due to the strong charge-density-wave fluctuations. The energy of the rotonlike minimum decreases with increasing the lattice velocity and it reaches zero at the critical velocity which is smaller than the pair breaking velocity. This indicates that the superfluid state is energetically unstable due to the spontaneous emission of the short-wavelength rotonlike excitations of the AB mode instead due to pair-breaking. We determine the critical velocities as functions of the interaction strength across the BCS-BEC crossover regime.

37 pages, 15 figures

References in corpus (9)

• Theory of ultracold Fermi gases
• Observation of the Pairing Gap in a Strongly Interacting Fermi Gas
• Crossover from a molecular Bose-Einstein condensate to a degenerate Fermi gas
• Evidence for Superfluidity of Ultracold Fermions in an Optical Lattice
• Bragg spectroscopy of a strongly interacting Fermi gas
• Critical velocity for superfluid flow across the BEC-BCS crossover
• The Josephson effect throughout the BCS-BEC crossover
• Collective modes and superflow instabilities of strongly correlated Fermi superfluids
• Stability of Superflow for Ultracold Fermions in Optical Lattices

Cited by in corpus (14)

• Roton-Maxon Excitation Spectrum of Bose Condensates in a Shaken Optical Lattice
• Rotonlike instability and pattern formation in spinor Bose-Einstein condensates
• Critical velocity of flowing supersolids of dipolar Bose gases in optical lattices
• Detecting the superfluid critical momentum of Bose gases in optical lattices through dipole oscillations
• Effects of periodic potentials on the critical velocity of superfluid Fermi gases in the BCS-BEC crossover
• Superfluidity of Dirac Fermions in a Tunable Honeycomb Lattice: Cooper Pairing, Collective Modes, and Critical Currents
• Dynamical structure factor of a fermionic supersolid on an optical lattice
• Flow-Induced Charge Modulation in Superfluid Atomic Fermions Loaded into an Optical Kagome Lattice
• Excitonic collective modes in Weyl semi-metals
• Aspects of Superfluid Cold Atomic Gases in Optical Lattices
• Collective excitation and stability of flow-induced gapless Fermi superfluids
• Spectrum of density, spin and pairing fluctuations of an attractive two-dimensional Fermi gas
• Speed of sound of a spin balanced Fermi gas with s- and d-wave pairings across the BCS-BEC evolution
• The attractive Hubbard model as an $SO(3)$ system of competing phases: supersolid order and its thermal melting