Spin transport in a unitary Fermi gas close to the BCS transition

TL;DR

This paper investigates how pairing fluctuations and pseudogap formation near the BCS transition affect spin transport properties in a two-component ultracold Fermi gas, using both Boltzmann and diagrammatic methods.

Contribution

It compares Boltzmann and diagrammatic approaches to analyze spin transport near the BCS transition, highlighting the effects of pseudogap physics and lifetime effects.

Findings

Qualitative agreement between the two approaches.

Transport coefficients differ quantitatively.

Pseudogap formation influences spin transport near the transition.

Abstract

We consider spin transport in a two-component ultracold Fermi gas with attractive interspecies interactions close to the BCS pairing transition. In particular, we consider the spin-transport relaxation rate and the spin-diffusion constant. Upon approaching the transition, the scattering amplitude is enhanced by pairing fluctuations. However, as the system approaches the transition, the spectral weight for excitations close to the Fermi level is decreased by the formation of a pseudogap. To study the consequence of these two competing effects, we determine the spin-transport relaxation rate and the spin-diffusion constant using both a Boltzmann approach and a diagrammatic approach. The former ignores pseudogap physics and finite lifetime effects. In the latter, we incorporate the full pseudogap physics and lifetime effects, but we ignore vertex corrections, so that we effectively calculate single-particle relaxation rates instead of transport relaxation rates. We find that there is qualitative agreement between these two approaches although the results for the transport coefficients differ quantitatively.