Cooper pairing above the critical temperature in a unitary Fermi gas

Abstract

We present an ab initio determination of spin responses of the unitary Fermi gas, based on finite temperature quantum Monte Carlo calculations and the Kubo linear-response formalism. We determine the temperature dependence of the spin susceptibility and the spin conductivity. We show that both quantities exhibit suppression above the critical temperature of the superfluid to normal phase transition due to presence of the Cooper pairs. The spin diffusion transport coefficient does not display the existence of a minimum in the vicinity of the critical temperature and it drops to very low values D_s approx 0.8hbar/m in the superfluid phase. All these spin observables show a smooth and monotonic behavior with temperature when crossing the critical temperature T_c, until the Fermi liquid regime is attained at the temperature T*, where the pseudogap regime disappears.