Temperature and coupling dependence of the "contact" for an ultracold Fermi gas

Daisuke Inotani, Yoji Ohashi

Santiago F. Caballero-Benítez, R. Paredes, Vı́ctor Romero-Rochı́n

F. Palestini, Andrea Perali, P. Pieri +1 more

Physical properties of an ultracold Fermi gas in the temperature-coupling phase diagram can be characterized by the contact intensity $C$, which enters the pair-correlation function at short distances and describes how the two-body problem merges into its surrounding. We show that the local order established by pairing fluctuations about the critical temperature ${T}_{c}$ of the superfluid transition considerably enhances the contact $C$ in a temperature range where pseudogap phenomena are maximal. Our ab initio results for $C$ in a trap compare well with recently available experimental data over a wide coupling range. An analysis is also provided for the effects of trap averaging on $C$.

E. D. Kuhnle, Sascha Hoinka, Paul Dyke +3 more

The contact I, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter 1/(k(F)a), where k(F) is the Fermi wave vector and a is the s-wave scattering length, and the temperature T/T(F), where T(F) is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.

Selim Jochim

Kenta Nagase, Soki Oshima, H. Takahashi +1 more

Using radio-frequency (rf) spectroscopy, we measure the $p$-wave contacts in a Fermi gas of $^{6}\mathrm{Li}$ atoms near the $p$-wave Feshbach resonance. The rf spectrum exhibits clear asymptotic behavior, characterized by ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\omega}}}^{\ensuremath{-}1/2}$ and ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\omega}}}^{\ensuremath{-}3/2}$ dependencies. The magnetic-field dependence of the $p$-wave contacts agrees reasonably well with the virial expansion theory in a detuned magnetic-field range, validating the theory near half of the Fermi temperature. The $p$-wave contacts measured in this article constitute a second data set, complementing the data obtained from the $^{40}\mathrm{K}$ system and contributing valuable insights into $p$-wave interactions in ultracold Fermi gases.