Spectral functions and rf response of ultracold fermionic atoms

Abstract

We present a calculation of the spectral functions and the associated rf response of ultracold fermionic atoms near a Feshbach resonance. The single particle spectra are peaked at energies that can be modeled by a modified BCS dispersion. However, even at very low temperatures their width is comparable to their energy, except for a small region around the dispersion minimum. The structure of the excitation spectrum of the unitary gas at infinite scattering length agrees with recent momentum-resolved rf spectra near the critical temperature. A detailed comparison is made with momentum integrated, locally resolved rf spectra of the unitary gas at arbitrary temperatures and shows very good agreement between theory and experiment. The pair size defined from the width of these spectra is found to coincide with that obtained from the leading gradient corrections to the effective field theory of the superfluid.

Thermodynamics of Ultracold Fermi Gases

“…This is in agreement with the observations of the MIT group [79] or several theoretical predictions using Monte Carlo calculations [67] or excitation spectrum calculations [179,180]: the super uid can be polarized for δ 1 1, which is beyond the parameter range addressed in this work. …”

“…In Fig.5.9 we compare the values of η c extracted from our data to lower bounds 1 − 2∆ 0 /µ 1 , using values of the gap measured by the MIT group in [166], or calculated in [179,60,182,158]. Quite surprisingly, the § In the BEC limit, it is possible to add extra majority atoms to a super uid without breaking it.…”

“…Comparison between the experimental η c values determined from our work (black dots) to the lower bounds 1 − 2∆ 0 /µ 1 provided by the single-particle excitation gap. The stars are given by the experimental ∆ 0 values from the MIT group [166], the open squares from diagrammatic calculations [179], the open circles from the most recent Fixed Node Monte Carlo calculations [60], the crosses from a Quantum Monte Carlo calculation extrapolated at T = 0 [182], and the open triangle from a zerotemperature Quantum Monte Carlo calculation [158].…”

Quasiparticle dispersions and lifetimes in the normal state of the BCS-BEC crossover

“…However previous studies using ab initio techniques [18] and self-consistent T-matrix theories [19] (where the bare propagators in Eq. (2) are replaced by the fully dressed propagator G) produce results with similar qualitative features.…”

Dilute Fermi and Bose gases

“…We can now integrate (80) over ω to obtain n(k) at large k. Actually the ω integral is precisely that in (65), which immediately yields the needed relation (78). Similar analyses can be applied to determine the the spectral functions of other observables [28,8,20,21,4,2,24].…”