Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan.
Physics Division, National Center for Theoretical Sciences, Hsinchu, 30013, Taiwan.
Sci Rep. 2016 Sep 16;6:33320. doi: 10.1038/srep33320.
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.
众所周知，当磁场强于某个临界值时，自旋不平衡会破坏电子的库珀对，从而阻碍自旋单重态通道中的超导性。然而，在超冷费米气体的双层系统中，我们证明通过包括自旋翻转隧道，低温下的临界磁场值可以显著增加，这在费米面附近打开了自旋三重态通道的能隙，从而降低了有效磁场对超流性的影响。当隧道超过临界值时，相变也从一级相变变为二级相变。考虑到实际实验，可以通过在两层之间施加相位差的层内拉曼耦合来实现这种机制，从而在自旋态之间产生隧道。
