Instability of superfluid Fermi gases induced by a rotonlike density mode in optical lattices

Journal Article · Tue Dec 15 00:00:00 EST 2009 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.80.063627· OSTI ID:21352419

Yunomae, Yoshihiro; Yamamoto, Daisuke ^[1]; Danshita, Ippei ^[2]; Yokoshi, Nobuhiko ^[3]; Tsuchiya, Shunji ^[4]

---

1. Department of Physics, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555 (Japan)
2. Department of Physics, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan)
3. Nanotechnology Research Institute, AIST, Tsukuba 305-8568 (Japan)
4. CREST-JST, 4-1-8 Honcho, Saitama 332-0012 (Japan)

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 Cote 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.

• OSTI ID: 21352419
• Journal Information: Physical Review. A, Vol. 80, Issue 6; Other Information: DOI: 10.1103/PhysRevA.80.063627; (c) 2009 The American Physical Society; ISSN 1050-2947
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
BOSE-EINSTEIN CONDENSATION
CRITICAL VELOCITY
DENSITY
EXCITATION
FERMI GAS
FLUCTUATIONS
GREEN FUNCTION
HUBBARD MODEL
RANDOM PHASE APPROXIMATION
RESPONSE FUNCTIONS
SPECTRA
SUPERFLUIDITY
APPROXIMATIONS
CALCULATION METHODS
CRYSTAL MODELS
ENERGY-LEVEL TRANSITIONS
FUNCTIONS
MATHEMATICAL MODELS
PHYSICAL PROPERTIES
VARIATIONS
VELOCITY