Abstract
For decades, the conventional view is that an s-wave BCS superfluid can not support uniform spin polarization due to a gap Δ in the quasiparticle excitation spectrum. We show that this is an artifact of the dismissal of quasiparticle interactions V qp in the conventional approach at the outset. Such interactions can cause triplet fluctuations in the ground state and hence non-zero spin polarization at “magnetic field” h<Δ. The resulting ground state is a pairing state of quasiparticles on the “BCS vacuum”. For sufficiently large V qp , the spin polarization of at unitarity has the simple form m ∝ μ 1/2. Our study is motivated by the recent experiments on Fermi gases with spin imbalance in the strongly interacting regime.
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Ho, TL., Zhai, H. Homogeneous Fermion Superfluid with Unequal Spin Populations. J Low Temp Phys 148, 33–41 (2007). https://doi.org/10.1007/s10909-007-9350-9
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DOI: https://doi.org/10.1007/s10909-007-9350-9