Yoav Sagi, Tara E. Drake, Rabin Paudel, Deborah S. Jin
The theory 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. An important universal quantity whose predicted value is sensitive to different theoretical approaches is the Tan contact of a homogeneous ensemble. Recently, we reported on the development of a technique to probe local properties of a trapped gas. Here we employ this technique and measure the local (homogeneous) contact of a unitary Fermi gas. We find a gradual decrease of the contact when the temperature is increased, with good agreement with the virial expansion at high temperatures. Several theoretical works predict an increase in the contact above the superfluid critical temperature, which we do not observe in the experiment. Out of the theories compared, our data agree best with the Nozieres-Schmitt-Rink approach with gaussian pair-fluctuations.
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http://arxiv.org/abs/1208.2067
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