Quantum Monte Carlo insights into the properties of the polarized Fermi gas around unitarity

Strongly correlated Fermi systems with pairing interactions become superfluid below a critical temperature Tc. The extent to which such pairing correlations alter the behavior of the liquid at temperatures T > Tc is a subtle issue that remains an area of debate, in particular regarding the appearance of the so-called pseudogap in the BCS-BEC crossover of unpolarized spin-1/2 nonrelativistic matter. To shed light on this issue, we extracted several quantities of crucial importance at and around the unitary limit, namely the odd-even staggering of the total energy, the spin susceptibility, the pairing correlation function, the condensate fraction, and the critical temperature Tc, using a nonperturbative, constrained-ensemble quantum Monte Carlo algorithm. We looked for signatures of the pseudogap at couplings between 0.0 ≤ 1/(kF a) ≤ 0.3. In particular, at 1/(kF a) = 0.3, we see strong pseudogap signatures, which diminish (but not necessarily vanish) as the coupling is varied towards unitarity.