Superconductivity enhanced by spin-flip tunnelling in the presence of a magnetic field
Junhui Zheng1*, Gediminas Juzeliunas2, Daw-Wei Wang1,3
1Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
2Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania
3Physics Division, National Center for Theoretical Sciences, Hsinchu, Taiwan
* presenting author:Jun-hui Zheng,
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 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 strongly enhanced by including a spin-flip tunnelling, which opens a gap in the spin-triplet channel near 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 is larger than a critical value. Considering a realistic experiment, this mechanism can be implemented by applying a Raman coupling between spins with a phase difference between the two layers. Similar results can be also obtained when considering a multi-layer system loaded into a 1D optical lattice.

Keywords: Ultra-cold atoms, Superconductivity, Bilayer system