The nature of pairing correlations in the homogeneous unitary Fermi gas*

The spin-balanced unitary Fermi gas is a strongly correlated many-body system that exhibits a high superfluid critical temperature of about 0.15 of the Fermi temperature. A pseudogap phase, which has a gapped single-particle excitation spectrum without off-diagonal long-range order, was proposed but its existence is still debated. To address this, we have carried out accurate finite-temperature auxiliary-field quantum Monte Carlo calculations of the homogeneous unitary gas on a lattice in the canonical ensemble of fixed particle number. We present results for the heat capacity, condensate fraction, model independent energy-staggering pairing gap, and static spin susceptibility as a function of temperature. We observe no clear signatures of a gapped phase above the superfluid critical temperature.