Phase separation and pair condensation in a spin-imbalanced 2D Fermi gas

TL;DR

This paper investigates phase separation and pair condensation in a 2D spin-imbalanced Fermi gas, revealing coexistence of phase-separated condensates and polarized pair condensates across various interaction strengths and polarizations.

Contribution

It provides experimental evidence of pair condensation in imbalanced 2D Fermi gases, including in regimes where phase separation is absent, highlighting the existence of polarized pair condensates.

Findings

Observation of in-trap phase separation with a spin-balanced condensate surrounded by polarized gas.

Detection of pair condensation at large polarizations where phase separation disappears.

Identification of zero momentum pair condensates in 2D spin-imbalanced gases.

Abstract

We study a two-component quasi-two-dimensional Fermi gas with imbalanced spin populations. We probe the gas at different interaction strengths and polarizations by measuring the density of each spin component in the trap and the pair momentum distribution after time of flight. For a wide range of experimental parameters, we observe in-trap phase separation characterized by the appearance of a spin-balanced condensate surrounded by a polarized gas. Our momentum space measurements indicate pair condensation in the imbalanced gas even for large polarizations where phase separation vanishes, pointing to the presence of a polarized pair condensate. Our observation of zero momentum pair condensates in 2D spin-imbalanced gases opens the way to explorations of more exotic superfluid phases that occupy a large part of the phase diagram in lower dimensions.