Final-state effects in radio-frequency spectrum of ultracold Fermions

Giancarlo Calvanese Strinati

Sourish Basu, Erich J. Mueller

We model the impact of final-state interactions on the radio frequency spectrum of a strongly interacting two-component superfluid Fermi gas. In addition to a broad asymmetric peak coming from the breakup of Cooper pairs, we find that, for appropriate parameters, one can observe a sharp symmetric "bound-bound" spectral line coming from the conversion of Cooper pairs in one channel to pairs or molecules in another.

André Schirotzek

Junjun Xu, Qiang Gu, Erich J. Mueller

We calculate the radio frequency (RF) spectrum of fermionic atoms near a narrow Feshbach resonance, explaining observations made in ultracold samples of ${}^{6}\mathrm{Li}$ [E. L. Hazlett et al., Phys. Rev. Lett. 108, 045304 (2012)]. We use a two channel resonance model to show that the RF spectrum contains two peaks. In the wide-resonance limit, nearly all spectral weight lies in one of these peaks, and typically the second peak is very broad. We find strong temperature dependence, which can be traced to the energy dependence of the two-particle scattering. In addition to microscopic calculations, we use sum rule arguments to find generic features of the spectrum which are model independent.

Andrea Perali, P. Pieri, Giancarlo Calvanese Strinati

The radio-frequency spectra of ultracold Fermi atoms are calculated by including final-state interactions affecting the excited level of the transition and compared with the experimental data. A competition is revealed between pairing-gap effects which tend to push the oscillator strength toward high frequencies away from threshold and final-state effects which tend instead to pull the oscillator strength toward threshold. As a result of this competition, the position of the peak of the spectra cannot be simply related to the value of the pairing gap, whose extraction thus requires support from theoretical calculations.

Selim Jochim