Abstract
It is well-known that when the magnetic field is stronger than a critical value, the spin imbalance can break the Cooper pairs of electrons and hence hinder the superconductivity in a spin-singlet channel. In a bilayer system of ultra-cold Fermi gases, however, we demonstrate that the critical value of the magnetic field at zero temperature can be significantly increased by including a spin-flip tunnelling, which opens a gap in the spin-triplet channel near the Fermi surface and hence reduces the influence of the effective magnetic field on the superfluidity. The phase transition also changes from first order to second order when the tunnelling exceeds a critical value. Considering a realistic experiment, this mechanism can be implemented by applying an intralayer Raman coupling between the spin states with a phase difference between the two layers.
Highlights
The superfluidity can not be affected by a relatively small effective magnetic field field acting on the singlet Cooper pairs
We have explored a new mechanism to greatly enhance superfluidity of ultracold Fermi gases in a large range of the effective magnetic field
A Raman coupling induces intralayer spin-flip transitions with a phase difference between the two layers. Such a Raman coupling serves as a magnetic field staggered in different layers
Summary
Zeeman field along the z-axis for both layers, with the interlayer tunneling becoming spin-dependent for sin φ ≠ 0. Our major aim is to study effects of the interlayer spin-flip tunneling (φ = π/2) on the superfluid properties for the bilayer system in the presence of magnetic field.
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