Effects of trap anisotropy on impurity scattering regime in a Fermi gas

TL;DR

This paper investigates how trap anisotropy influences impurity scattering regimes in a Fermi gas, revealing coexistence of collisionless and hydrodynamic behaviors and their effects on oscillation modes and expansion dynamics.

Contribution

It provides a detailed numerical analysis of impurity scattering effects in anisotropic traps, highlighting the transition between different dynamical regimes in a Fermi gas.

Findings

Coexistence of collisionless and hydrodynamic behaviors in low-lying modes.

Aspect ratio of expanding cloud depends on collision time.

Trap anisotropy significantly affects impurity scattering regimes.

Abstract

We evaluate the low-lying oscillation modes and the ballistic expansion properties of a harmonically trapped gas of fermionic K40 atoms containing thermal Rb87 impurities as functions of the anisotropy of the trap. Numerical results are obtained by solving the Vlasov-Landau equations for the one-body phase-space distribution functions and are used to test simple scaling Ansatzes. Starting from the gas in a weak impurity-scattering regime inside a spherical trap, the time scales associated to motions in the axial and azimuthal directions enter into competition as the trap is deformed to an elongated cigar-like shape. This competition gives rise to coexistence of collisionless and hydrodynamic behaviors in the low-lying surface modes of the gas as well as to a dependence of the aspect ratio of the expanding cloud on the collision time.