Dynamical cluster quantum Monte Carlo study of the single-particle spectra of strongly interacting fermion gases

We study the single-particle spectral function of resonantly interacting fermions in the unitary regime, as described by the three-dimensional attractive Hubbard model in the dilute limit. Our approach, based on the dynamical cluster approximation and the maximum entropy method, shows the emergence of a gap with decreasing temperature, as reported in recent cold-atom photoemission experiments, for coupling values that span the BEC-BCS crossover. By comparing the behavior of the spectral function to that of the imaginary time dynamical pairing susceptibility, we attribute the development of the gap to the formation of local bound atom pairs.