Deformation of a Trapped Fermi Gas with Unequal Spin Populations

TL;DR

This paper investigates how a polarized, strongly-interacting Fermi gas of lithium-6 atoms deforms at low temperatures, revealing phase separation and a possible tricritical point in its phase diagram.

Contribution

It provides experimental evidence of deformation behaviors and phase boundaries in a polarized Fermi gas, highlighting temperature-dependent phase separation phenomena.

Findings

Unpolarized core deforms with polarization at low temperatures.

Sharp phase boundaries indicate first-order phase transition.

Presence of a partially-polarized shell at higher temperatures.

Abstract

The real-space densities of a polarized strongly-interacting two-component Fermi gas of $^6$Li atoms reveal two low temperature regimes, both with a fully-paired core. At the lowest temperatures, the unpolarized core deforms with increasing polarization. Sharp boundaries between the core and the excess unpaired atoms are consistent with a phase separation driven by a first-order phase transition. In contrast, at higher temperatures the core does not deform but remains unpolarized up to a critical polarization. The boundaries are not sharp in this case, indicating a partially-polarized shell between the core and the unpaired atoms. The temperature dependence is consistent with a tricritical point in the phase diagram.