Collisions in zero temperature Fermi gases

TL;DR

This paper investigates the collision dynamics of zero-temperature two-component Fermi gases, revealing that Pauli blocking minimally affects momentum-changing collisions, allowing hydrodynamic behavior without superfluidity evidence.

Contribution

It demonstrates that Pauli blocking has limited impact on collision rates in Fermi gases, challenging previous assumptions about hydrodynamic expansion indicating superfluidity.

Findings

Pauli blocking is minor for momentum-changing collisions.

High scattering cross-section leads to hydrodynamic expansion.

Hydrodynamic behavior does not necessarily imply superfluidity.

Abstract

We examine the collisional behavior of two-component Fermi gases released at zero temperature from a harmonic trap. Using a phase-space formalism to calculate the collision rate during expansion, we find that Pauli blocking plays only a minor role for momentum changing collisions. As a result, for a large scattering cross-section, Pauli blocking will not prevent the gas from entering the collisionally hydrodynamic regime. In contrast to the bosonic case, hydrodynamic expansion at very low temperatures is therefore not evidence for fermionic superfluidity.