Two-band description of resonant superfluidity in atomic Fermi gases

Journal Article · Mon Feb 23 00:00:00 EST 2015 · Physical Review A - Atomic, Molecular, and Optical Physics

DOI:https://doi.org/10.1103/PhysRevA.91.023622· OSTI ID:1246953

He, Lianyi ^[1]; Hu, Hui ^[2]; Liu, Xia -Ji ^[2]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Swinburne Univ. of Technology, Victoria (Australia)

Fermionic superfluidity in atomic Fermi gases across a Feshbach resonance is normally described by the atom-molecule theory, which treats the closed channel as a noninteracting point boson. In this work we present a theoretical description of the resonant superfluidity in analogy to the two-band superconductors. We employ the underlying two-channel scattering model of Feshbach resonance where the closed channel is treated as a composite boson with binding energy ε₀ and the resonance is triggered by the microscopic interchannel coupling U₁₂. The binding energy ε₀ naturally serves as an energy scale of the system, which has been sent to infinity in the atom-molecule theory. We show that the atom-molecule theory can be viewed as a leading-order low-energy effective theory of the underlying fermionic theory in the limit ε₀→∞ and U₁₂→0, while keeping the phenomenological atom-molecule coupling finite. The resulting two-band description of the superfluid state is in analogy to the BCS theory of two-band superconductors. In the dilute limit ε₀→∞, the two-band description recovers precisely the atom-molecule theory. The two-band theory provides a natural approach to study the corrections because of a finite binding energy ε₀ in realistic experimental systems. For broad and moderate resonances, the correction is not important for current experimental densities. However, for extremely narrow resonance, we find that the correction becomes significant. Lastly, the finite binding energy correction could be important for the stability of homogeneous polarized superfluid against phase separation in imbalanced Fermi gases across a narrow Feshbach resonance.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: AC02-05CH11231; FT140100003; FT130100815; DP140103231; DP140100637; AC52-06NA25396
• OSTI ID: 1246953
• Alternate ID(s): OSTI ID: 1180994
• Report Number(s): LA-UR-14-28538; PLRAAN
• Journal Information: Physical Review A - Atomic, Molecular, and Optical Physics, Vol. 91, Issue 2; ISSN 1050-2947
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
Feshbach resonance
two-band superconductor
Fermi superfluidity