Spectral study of a unitary Fermi gas

We study the single particle spectral function of a unitary Fermi gas, based on a pairing fluctuation theory for Fermi superfluidity which is derived via an equation of motion approach. In particular, the self energy induced from finite-momentum incoherent pairing fluctuations is calculated with a high quantitative accuracy involving elaborate numerical convolution between pair and hole propagators. The important particle-hole fluctuations are also taken into account. I will present direct comparison with recent experimental measurement [Nature 626, 288 (2024)] using a momentum-resolved microwave spectroscopy in a unitary gas Li-6, and will show that our calculations are in quantitatively good agreement with experiment, in terms of the Bogoliubov quasiparticle dispersion, the energy distribution curve, the temperature dependence of the spectral gap, and the pair decay rate. This supports both the concept of a pseudogap in unitary Fermi gases and our pairing fluctuation theory for Fermi superfluidity, which features naturally a pseudogap when the pairing interaction becomes strong.