Achieving a BCS transition in an atomic Fermi gas

TL;DR

This paper demonstrates how to convert a molecular Bose-Einstein condensate into a degenerate atomic Fermi gas exhibiting BCS pairing by tuning the scattering length, achieving very low temperatures relative to the Fermi temperature.

Contribution

It shows that adiabatically changing the scattering length from positive to negative can induce a BCS transition in an atomic Fermi gas, bridging BEC and BCS regimes.

Findings

Achieved a temperature ratio T/T_F ~ 10^{-2} in the degenerate Fermi gas.

Identified the critical value of k_F|a| ≈ 0.5 for the BCS transition.

Demonstrated the feasibility of transforming a molecular BEC into a Fermi gas with BCS pairing.

Abstract

We consider a gas of cold fermionic atoms having two spin components with interactions characterized by their s-wave scattering length $a$. At positive scattering length the atoms form weakly bound bosonic molecules which can be evaporatively cooled to undergo Bose-Einstein condensation, whereas at negative scattering length BCS pairing can take place. It is shown that, by adiabatically tuning the scattering length $a$ from positive to negative values, one may transform the molecular Bose-Einstein condensate into a highly degenerate atomic Fermi gas, with the ratio of temperature to Fermi temperature $T/T_F \sim 10^{-2}$. The corresponding critical final value of $k_{F}|a|$ which leads to the BCS transition is found to be about one half, where $k_F$ is the Fermi momentum.