Density, spin, and pairing instabilities in polarized ultracold Fermi gases

TL;DR

This paper investigates how population imbalance affects pairing, spin, and density instabilities in a polarized ultracold Fermi gas after a sudden interaction quench, revealing potential for FFLO states and phase separation.

Contribution

It provides a detailed analysis of the dynamical instabilities in polarized Fermi gases near a Feshbach resonance, highlighting the conditions for FFLO-like states and phase separation.

Findings

Finite momentum pairing dominates the pairing instability, indicating FFLO-like states.

Density instabilities on the BCS side suggest phase separation precursors.

Pairing instability on the BEC side depends on scattering length, weakly influenced by population imbalance.

Abstract

We study the influence of population imbalance on the pairing, spin, and density instabilities of a two component ideal Fermi gas after a sudden quench of interactions near a Feshbach resonance. Over a large region of parameters the pairing instability is dominated by finite momentum pairing, suggesting the possibility of observing FFLO-like states in the unstable initial dynamics. Long-wavelength density instabilities are found on the BCS side of the resonance, and are interpreted as a precursor of the phase separation expected at equilibrium. On the BEC side of the resonance, the pairing instability is present for scattering lengths that are larger than a critical value that is only weakly dependent on population imbalance and always smaller than the scattering length at which the Stoner-like spin instability occurs.