Homogeneous Fermion Superfluid with Unequal Spin Populations

Abstract

For decades, the conventional view is that an s-wave BCS superfluid can not support uniform spin polarization due to a gap $\Delta$ 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" $h<\Delta$. 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 $m\propto {\mu }^{1/2}$. Our study is motivated by the recent experiments at Rice which found evidence of a homogenous superfluid state with uniform spin polarization.

4 pages, 3 figures

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Cited by in corpus (7)

• Direct Observation of the Superfluid Phase Transition in Ultracold Fermi Gases
• Fulde-Ferrell-Larkin-Ovchinnikov states in one-dimensional spin-polarized ultracold atomic Fermi gases
• Non-BCS superfluidity in trapped ultracold Fermi gases
• Out-of-Equilibrium Spin Transport in Mesoscopic Superconductors
• Dimensional Crossover in a Spin-imbalanced Fermi gas
• Asymmetric Fermion Superfluid with Inter- and Intra-Species Pairings
• Pairing in Asymmetrical Fermi Systems with Intra- and Inter-Species Correlations