Superfluidity in Strongly Interacting Spin-Polarized Fermi Gases

We report measurements of phase separation in a harmonically trapped, spin polarized two-component Fermi gas. The interactions in the gas are varied using a magnetically-tuned Feshbach resonance between the weakly-interacting BCS and strongly-interacting BEC regimes. Using spin-selective imaging, we measure the density profiles for the two lowest hyperfine levels of $^6$Li, with the superfluid phase being indicated by an unpolarized central core. We determine phase boundaries for the superfluid transition as a function of interactions and polarization, finding results that are consistent with earlier experimental results in the crossover regime\footnote{M. Zwierlein et al., Science {\bf 311}, 492 (2006); N. Navon et al., Science {\bf 328}, 729 (2010)}. We also explore the BEC side of resonance, where we compare our measurements to Quantum Monte Carlo simulations\footnote{G. Bertaina and S. Giorgini, PRA {\bf 79}, 013616 (2009)}, and also the deep BCS regime, where few theoretical predictions are available.