Measuring the spectral function of a strongly interacting Fermi gas

We present a novel measurement of the single-particle spectral function for a homogeneous Fermi gas above the critical temperature for superfluidity throughout the BCS-BEC crossover. The data show signatures of both Fermi liquid behavior and pairing. We find that the data fit well to a two-component function that includes fermionic quasiparticles and an ``incoherent background'' that is modeled using the dispersion of thermal molecules. As the strength of interactions is increased, the quasiparticle spectral weight vanishes, which signals the breakdown of a Fermi liquid description.