Formation of bright solitons and soliton trains in a fermion-fermion mixture by modulational instability

TL;DR

This paper investigates how bright solitons and soliton trains can form in a fermion-fermion mixture using a mean-field model, highlighting the role of modulational instability and interspecies interactions.

Contribution

It demonstrates the formation and stability of fermionic bright solitons and trains via modulational instability, with analysis supported by variational, numerical, and stability methods.

Findings

Bright solitons form for attractive interspecies interactions.

Soliton trains can be generated by changing interaction from repulsive to attractive.

Stable fermionic solitons are achievable with current laboratory technology.

Abstract

We employ a time-dependent mean-field-hydrodynamic model to study the generation of bright solitons in a degenerate fermion-fermion mixture in a cigar-shaped geometry using variational and numerical methods. Due to a strong Pauli-blocking repulsion among identical spin-polarized fermions at short distances there cannot be bright solitons for repulsive interspecies interactions. Employing a linear stability analysis we demonstrate the formation of stable solitons due to modulational instability of a constant-amplitude solution of the model equations for a sufficiently attractive interspecies interaction. We perform a numerical stability analysis of these solitons and also demonstrate the formation of soliton trains by jumping the effective interspecies interaction from repulsive to attractive. These fermionic solitons can be formed and studied in laboratory with present technology.