Observation of pseudogap phase is a strongly interacting Fermi gas*

We demonstrate that a pseudogap phase exists above the superfluid phase transition in an atomic Fermi gas. To observe this pseudogap phase we make two independent measurements. First, we make a direct measurement of the superfluid phase transition temperature by probing pair condensation in momentum space. Second, we probe the single-particle spectral function using an analog to photoemission spectroscopy which gives us the density of states and the dispersion E(k). In our measurements, we observe no qualitative change in the single-particle spectral function even as the temperature of the Fermi gas is increased from below to above the superfluid transition temperature. This is the first model-independent evidence for a pseudogap in atomic Fermi gases.