Tue, Dec 4, 2012, 2:00 pm to 3:30 pm
Joseph Henry Room
The collective behavior of an ensemble of strongly interacting fermions is central to many physical systems including liquid 3He, high-Tc superconductors, quark-gluon plasma, neutron stars, and ultracold Fermi gases. However, theoretical understanding of strongly interacting fermions is challenging due to the many-body nature of the problem and the fact that there is no obvious small parameter for a perturbative analysis. Ultracold atomic Fermi gases are ideal to shed light on this issue, as they provide excellent controllability, reproducibility, and unique detection methods. One of the problems, however, which complicates the interpretation of these experiments, is the inherent density inhomogeneity of the gas which arises due to the harmonic confinement. We have developed a technique to overcome this difficulty by selectively probing atoms near the center of a trapped gas while still retaining momentum resolution. For a weakly interacting Fermi gas of 40K atoms, we present measurements of the momentum distribution that reveal for the first time a sharp Fermi surface. We then apply the technique to a strongly interacting Fermi gas at the Feshbach resonance, where we probe the temperature dependence of the homogeneous Tan’s contact. Finally, we combine the technique with momentum resolved photoemission spectroscopy to study the outstanding issue of the nature of the normal state just above the superfluid transition temperature.