Dark soliton collisions in superfluid Fermi gases

TL;DR

This study investigates dark soliton collisions in a one-dimensional superfluid Fermi gas across the BEC-BCS crossover, revealing inelastic collisions and energy emission, with implications for understanding superfluid dynamics.

Contribution

The paper introduces a finite-temperature effective field theory to simulate dark soliton collisions in superfluid Fermi gases, highlighting inelastic effects and energy emission during collisions.

Findings

Collisions cause a spatial shift in soliton trajectories.

Inelastic collisions emit energy as density oscillations.

Dispersion relation matches superfluid collective excitations.

Abstract

In this work dark soliton collisions in a one-dimensional superfluid Fermi gas are studied across the BEC-BCS crossover by means of a recently developed finite-temperature effective field theory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015)] . The evolution of two counter-propagating solitons is simulated numerically based on the theory's nonlinear equation of motion for the pair field. The resulting collisions are observed to introduce a spatial shift into the trajectories of the solitons. The magnitude of this shift is calculated and studied in different conditions of temperature and spin-imbalance. When moving away from the BEC-regime, the collisions are found to become inelastic, emitting the lost energy in the form of small-amplitude density oscillations. This inelasticity is quantified and its behavior analyzed and compared to the results of other works. The dispersion relation of the density oscillations is calculated and is demonstrated to show a good agreement with the spectrum of collective excitations of the superfluid.