Non-BCS superfluidity in trapped ultracold Fermi gases

Abstract

Superconductivity and superfluidity of fermions require, within the BCS theory, matching of the Fermi energies of the two interacting Fermion species. Difference in the number densities of the two species leads either to a normal state, to phase separation, or - potentially - to exotic forms of superfluidity such as FFLO-state, Sarma state or breached pair state. We consider ultracold Fermi gases with polarization, i.e. spin-density imbalance. We show that, due to the gases being trapped and isolated from the environment in terms of particle exchange, exotic forms of superfluidity appear as a shell around the BCS-superfluid core of the gas and, for large density imbalance, in the core as well. We obtain these results by describing the effect of the trapping potential by using the Bogoliubov-de Gennes equations. For comparison to experiments, we calculate also the condensate fraction, and show that, in the center of the trap, a polarized superfluid leads to a small dip in the central density difference. We compare the results to those given by local density approximation and find qualitatively different behavior.

Extended and revised, 13 pages, 13 figures

References in corpus (13)

• Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas
• Direct Observation of the Superfluid Phase Transition in Ultracold Fermi Gases
• Normal state of a polarized Fermi gas at unitarity
• Deformation of a Trapped Fermi Gas with Unequal Spin Populations
• Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture
• Induced P-wave Superfluidity in Asymmetric Fermi Gases
• Generic Phase Diagram of Fermion Superfluids with Population Imbalance
• Surface Tension in Unitary Fermi Gases with Population Imbalance
• Mean field thermodynamics of a spin-polarized spherically trapped Fermi gas at unitarity
• Breakdown of the local density approximation in interacting systems of cold fermions in strongly anisotropic traps
• Normal-Superfluid Interface Scattering For Polarized Fermion Gases
• Homogeneous Fermion Superfluid with Unequal Spin Populations
• Response to Comment on "Pairing and Phase Separation in a Polarized Fermi Gas"

Cited by in corpus (4)

• FFLO state in 1, 2, and 3 dimensional optical lattices combined with a non-uniform background potential
• Exotic superfluid states of lattice fermions in elongated traps
• Population imbalanced fermions in harmonically trapped optical lattices
• Spin-imbalanced ultracold Fermi gases in a two-dimensional array of tubes