Light scattering in Cooper-paired Fermi atoms

TL;DR

This paper provides a comprehensive theoretical analysis of light scattering in superfluid Fermi gases, highlighting the effects of polarization, final state interactions, and the superfluid gap on the response function and dynamic structure factor.

Contribution

It introduces a polarization-selective light scattering scheme and calculates the response function using Nambu-Gorkov formalism, advancing understanding of superfluid Fermi gas responses.

Findings

Polarization significantly influences Cooper-pair response.

Selective scattering can excite single spin-component excitations.

Dynamic structure factor shows reduced gradient below 2Δ energy transfer.

Abstract

We present a detailed theoretical study of light scattering off superfluid trapped Fermi gas of atoms at zero temperature. We apply Nambu-Gorkov formalism of superconductivity to calculate the response function of superfluid gas due to stimulated light scattering taking into account the final state interactions. The polarization of light has been shown to play a significant role in response of Cooper-pairs in the presence of a magnetic field. Particularly important is a scheme of polarization-selective light scattering by either spin-component of the Cooper-pairs leading to the single-particle excitations of one spin-component only. These excitations have a threshold of $2\Delta$ where $\Delta$ is the superfluid gap energy. Furthermore, polarization-selective light scattering allows for unequal energy and momentum transfer to the two partner atoms of a Cooper-pair. In the regime of low energy ($<< 2\Delta$) and low momentum ($<2\Delta/(\hbar v_F)$, $v_F$ being the Fermi velocity) transfer, a small difference in momentum transfers to the two spin-components may be useful in exciting Bogoliubov-Anderson phonon mode. We present detailed results on the dynamic structure factor (DSF) deduced from the response function making use of generalized fluctuation-dissipation theorem. Model calculations using local density approximation for trapped superfluid Fermi gas shows that when the energy transfer is less than $2\Delta_0$, where $\Delta_0$ refers to the gap at the trap center, DSF as a function of energy transfer has reduced gradient compared to that of normal Fermi gas.